Vitamin D is essential for health. It has always been related to the strength of the bones. Now it is also known that it is involved in the functioning of almost all the organs and tissues, since its intake is essential for the metabolic processes that take place in the intestine, the brain, heart, pancreas, skin, and lymphocytes.
Apart from being important to keep the bones and teeth strong and healthy, vitamin D is also key to prevent the development of several diseases, such as cardiovascular diseases, cancer, rickets, psoriasis, and other pathologies, such as the premenstrual syndrome, back and bones pain, osteoporosis, hypertension, type I diabetes, Alzheimer’s disease, rheumatoid arthritis, depression, neurological disorders, immune system disorders (multiple sclerosis). To sum up, a vitamin D deficiency leads, in the long term, to the development of diseases.
- 1 Effects of vitamin D on health
- 2 Vitamin D, the powerful protective shield
- 3 Vitamin D protects health and prevents the onset of the following diseases:
- 4 How can we meet the daily requirements of vitamin D?
- 5 Vitamin D and the Sun
- 6 Vitamin D and the solarium
- 7 The Intake of vitamin D through dietary supplements
- 8 Who can benefit from the intake of vitamin D dietary supplements?
- 9 Vitamin D3 or D2: which one is better?
- 10 The enrichment of foods with vitamin D
- 11 How can we measure vitamin D3 levels
- 12 Vitamin D capsules, vitamin D tablets, or vitamin D drops, which format is the best?
- 13 How to combine Vitamin D with Vitamin K correctly
- 14 Conversion of vitamin D: from mcg to IU
- 15 What is vitamin D made of?
- 16 Vitamin D and the immune system
- 17 Vitamin D and osteoporosis
- 18 Vitamin D and depression
- 19 Vitamin D and inflammation
- 20 Vitamin D and Alzheimer’s disease
- 21 Vitamin D and sports
- 22 Vitamin D and testosterone
- 23 The use of vitamin D in the military field
- 24 The side effects of vitamin D
- 25 Bibliography:
- 26 Related Entries:
Effects of vitamin D on health
Vitamin D is involved in many metabolic processes and it is crucial for several functions of the organism:
- Functioning of the bones and joints
- Strong teeth
- Controlling the absorption of calcium in the intestine
- Functioning of the immune system and protecting against infections
- Endogenous synthesis of antibiotics
- Proper functioning of the muscles
- Cell division process
- Reducing the inflammation in the body
- Hormone balance
- Reducing oxidative stress
- Optimal transmission of signals between the cells
- Healthy and restful sleep
- Good adaptation to stress
- Proper intellectual performance
- Focus and wellbeing
- Sport Performance
Vitamin D, the powerful protective shield
According to a study conducted by the University of Oxford, the genes of any part of the body need to receive an adequate amount of vitamin D in order to avoid the development of diseases. Our genes need vitamin D to function normally. The gene receptors of our body need enough vitamin D to prevent the onset of diseases and function optimally.
A lack of vitamin D can trigger serious diseases, which is the reason why its intake is very important in order to maintain our health.
Clinical studies have proven that a vitamin D deficiency is related to many pathologies, diseases, and serious disorders.
Vitamin D protects health and prevents the onset of the following diseases:
- Autoimmune diseases
- Bone diseases (including rickets)
- Back and bones pain
- Cardiovascular diseases
- Chronic inflammation
- Immune system disorders
- Muscle weakness
- Rheumatoid arthritis
- Neurological diseases
It Protects Against Colds
A low level of vitamin D increases the risk of suffering colds and respiratory tract diseases in a 40%. This information was confirmed with the evaluation of 19000 people that had vitamin 25 (OH), a value for vitamin D between 10 to 29 ng/ml on average.
This relation increases even more in patients with asthma. Even though a direct relation has not been proven yet, it has been proven that vitamin D protects from colds.
It reduces the Risk of Suffering Diabetes
Vitamin D protects the cells from the pancreas that produce insulin. It also increases the insulin sensitivity, since it helps to transport the sugar to the cells much more faster through the blood. In general, it reduces the risk of developing diabetes.
It strengthens the bones
Vitamin D is in charge of making sure that the calcium is absorbed by the body through the intestine. Along with vitamin K2, it performs a key task in the bones metabolism, specially for building bone mass and for the preservation of a firm bone structure. Its deficiency in the organism increases the risk of suffering from osteoporosis and bone fractures.
It increases the intellectual performance
People with high levels of vitamin D can concentrate better, have a higher attention spawn, and are faster when processing information as oppose to those patients with a vitamin D deficiency. This conclusion was reached by researchers at the British University of Manchester in a European study carried out on 3000 men of ages ranging between 40-79 years.
In conclusion, those people with a high level of vitamin D can focus better and have more mental agility to process information.
It strengthens the muscles
A lack of vitamin D can produce muscle weakness and reduce the optimal functioning of the muscles, which results in an increased risk of suffering falls that produce bone fractures.
Clinical studies have proven that old people with a low level of vitamin D tend to fall more. The intake of vitamin D through a dietary supplement reduces the risk of suffering a bone fracture from falling in a 22%.
A vitamin D deficiency also weakens the quads and the muscles from the leg, reduces the performance and response time of the muscles and produces a bad body posture, which can even cause injuries.
It protects against other diseases
Vitamin D regulates several genetic functions that help to reduce the cell proliferation. Nowadays, many clinical studies claim that high levels of vitamin D in blood reduce up to a 40 or 50 per cent the risk of developing certain types of cancer, such as breast or colon cancer.
This is due to the fact that vitamin D counters the degeneration of the cells and, therefore, avoids the formation of tumors. Even with low levels of vitamin D (400 IU) the risk of suffering breast cancer can be reduced to a 24 per cent.
There are studies that link cancer to the geographical area where the patient lives. In certain types of cancer there is a direct relation between the disease and the degree of exposure to the sun of those who are affected by it.
How can we meet the daily requirements of vitamin D?
Vitamin D can be obtained in several ways:
- Through sunbathing. Most of the skin (face, arms, and legs) have to be exposed to the sun for a certain amount of time (around twenty minutes daily) in order to be effective.
- Using dietary supplements.
- Through the diet. However, the amount of vitamin D that is found in food is too low to meet the daily demands of the body. On average, people normally consume from 80 to 160 IU (2 to 4 mcg) of vitamin D through their daily diet. Read more about Foods with Vitamin D
Vitamin D and the Sun
How do we produce vitamin D through the sun radiation? Vitamin D is the only vitamin which is not mainly obtained from foods, but also through the sun rays. The electromagnetic radiation from the sun, when it falls directly on the skin, produces vitamin D. The intensity of UV-B sun radiation is responsible for the skin tan.
Even though we may think that is quite easy to access the necessary supply of vitamin D, since it is enough to expose ourselves to the light, unfortunately today’s society is not like that. One of the reasons is the increased fear of skin cancer.
Moreover, due to the lifestyle of the big cities and the long-working hours in closed spaces, most people do not receive enough sunlight, which is the reason why they suffer a vitamin D deficiency.
This problem is even more serious in northern countries or in very industrial areas.
The sun is the most important source of vitamin D, since it is produced when we expose our body to the UVB rays. In summer, the process is carried out quickly. It has been absorbed by the organism before the skin turns red. During this period, there is no risk of being sun burnt.
The amount of vitamin D that is produced by the organism depends on multiple factors: type of skin, location, season of the year, time of the day, clouds, and amount of skin exposed to the sun. The age also plays an essential role because as we age, it is more difficult for the body to produce vitamin D.
In order to get the requirements of vitamin D during the months of summer, it is advisable, if you are fair-skinned, to carry out a direct exposure to the sun at 10 o’clock in the morning, with your swimsuit and no sunscreen on from 10 to 20 minutes (depending on the type of skin). This routine for three days a week will provide the optimal amount of vitamin D that the body needs.
People with a dark skin produce less vitamin D due to their pigmentation and, therefore, must sunbathe for a longer period of time than fair-skinned people.
It is important to know that when we apply sunscreen our body will not produce vitamin D. This is due to the fact that the protector blocks the UVB rays. It is believed that a protector with a protection index of 8 already blocks vitamin D up to a 95%. Therefore, it is recommended to apply the sunscreen 10-20 minutes after being exposed to the sun.
Moreover, all the countries that are on the north of the 40 parallel (over the city of Rome) do not receive an adequate supply of vitamin D during the months between October to March. That is why it is necessary to use vitamin D dietary supplements during winter. At this time, not even walking with the face, arms, and legs exposed to the sun is enough.
It is recommended to apply sunscreen after that 10 to 20 minutes period to avoid sun burns and skin problems. Once the skin is already tan, you can spend more time sunbathing without protection, since the melanin that is formed on the skin acts as a natural sunscreen.
High levels of calcium in the blood also reduce the production of vitamin D.
The vitamin D deposits that the organism receives during the summer are eliminated in approximately two months if we do not sunbathe, or if we do not take vitamin D dietary supplements. The intake of vitamin D through the diet does not meet the daily requirements of the organism.
Factors that influence the production of vitamin D through the sun
During the summer, outdoors, and wearing a swimsuit, the body can produce 10.000 or 20.000 IU (international units) of vitamin D in less than an hour.
The production of vitamin D through the light is much better than consuming vitamin D through food, since its levels in the blood are maintained for a longer period of time than we they are administered orally.
However, the amount of vitamin D that the body can produce from electromagnetic radiations depends on several factors:
- Latitude or location
- Time of the year
- Time of the day
- Type of skin
- Clothes/Areas of the skin that is exposed to radiations
- Use of sunscreen
- Position and exposure to the sun: laying down/ standing
How is vitamin D produced on the skin?
The invisible UV-B rays, with a wavelength of 290-315 nanometers, are in charge of producing vitamin D on the skin.
This light goes through the superior layers of the skin tissue and it is transformed, through photolysis, into the so-called pre-vitamin D, which is a form of cholesterol (7-dehydrocholesterol) that in the second phase transforms into vitamin D due to the effect of the heat.
If we are still sunbathing after pre-vitamin D is produced, the new molecules become inactive in order to protect the organism from a vitamin D overdose.
For this reason, it is not possible to suffer a vitamin D overdose due to sun exposure, since the body has a protection mechanism with which to defend itself from an excessive vitamin D synthesis.
Through the different stages, vitamin D is transformed in the liver, on the first place, in 25-OH-vitamin D, whose levels can be measured through a blood analysis. But this is not the real form of vitamin D.
The real form of vitamin D is 1.25-dihydroxy-vitamin D, which is formed in the organism according to the demands of the body.
Vitamin D and sunlight: the influence of the time of the day and the latitude when we sunbathe
The amount of UV-B radiation of the sun that reaches us depends both on the clouds and the angle of the light. The more plain the angle is, the longer is the distance that the sun rays must cross until they reach the ozone layer, until the UV radiation is absorbed by the dermis.
If the angle of the radiations is lower than 45 degrees no absorption of the rays will take place, nor vitamin D will be generated. This is what happens at dawn, during the nights, and during the months of winter, since the intensity of the UV radiation is too low in order to produce vitamin D.
To the north of 40 degrees latitude, around Rome, the production of vitamin D is extremely limited during the months between October and March. During this time, the position of the radiations is too low to ensure a proper supply of vitamin D.
The golden rule to check if vitamin D is being produced consists on checking the shadow of the body: if it is longer than the height, almost no vitamin D is produced.
Differences between UV-B and UV-A rays
Only UV-B rays produce vitamin D. This represents just between a 2-10% of ultraviolet radiation. Most of the UV rays are made of UV-A radiation, that goes deeper into the dermis and also causes more damage. Both forms of ultraviolet light are very different:
- Direct tanning, but the tan last only a few hours
- They do not protect the skin tissue through pigmentation
- They do not produce vitamin D
- They do not cause burns
- They produce the aging of the skin
- They produce big amounts of free radicals
- They increase the risk of suffering a malign melanoma
- Slow and long-lasting tan
- They protect the skin tissue through pigmentation
- They produce vitamin D
- They produce burns
- They do not cause the aging of the skin
- Low production of free radicals
- They increase the risk of white skin cancer (basal cell carcinoma and scaly cell carcinoma)
The UV-A rays are the ones that entail risks for health, while the UV-B rays can cause burns, but at the same time they produce vitamin-D.
The production of vitamin D through radiation according to the time of the day
The intensity of the UV-B radiation changes a lot throughout the day and it is more intense in the afternoon. In this moments, the production of vitamin D is higher.
Relative intensity of UV radiation
Time: Since the sun comes out to 9:00h
- Relative intensity * UVA—60%
- Relative intensity UV-B—–12.5%
Time: From 09 a.m. to 11 a.m.
- Relative intensity * UVA— 90%
- Relative intensity UV-B—–20%
Time: From 11 a.m.-13 h.
- Relative intensity * UVA— 95%
- Relative intensity UV-B—–25%
Time: 13 h.
- Relative intensity * UVA— 100%
- Relative intensity UV-B—–100%
Time: From 13 h-15
- Relative intensity UVA— 95%
- Relative intensity UV-B—–95%
Time: From 15-17 h
- Relative intensity * UVA— 90%
- Relative intensity UV-B—–20%
Time: From 17 h to the setting of the sun
- Relative intensity * UVA—-60%
- Relative intensity UV-B—–12.5%
* The relative intensity describes the intensity according to the maximum radiation daily.
As this information shows, the production of vitamin D through UV-B radiation is higher between 11 and 15 o’clock, which are the “hours with more intense radiations”, which is the reason why only a short exposure to the sun is needed to produce vitamin D.
However, the intensity of the UV rays does not always correlate to the production of vitamin D, so we do not always produce the same amount of vitamin D. Although generally speaking, the afternoon sun produces twice the vitamin D of the setting sun.
The incidence angle of the sun on the skin tissue
The production of vitamin D also depends on the angle of the radiations when they fall on the skin: the production of vitamin D is much lower when walking or standing than if we are laying down. The best way to produce vitamin D consists on sunbathing while laying down on the beach or at the pool.
Vitamin D, the sun, and the type of skin
The amount of radiations that are needed to generate vitamin D can change a lot according to the external conditions. But, even with the same external conditions, the individual factors of each person are also relevant.
First of all, the amount of vitamin D that each person produces depends the type of skin. At this level, the amount of vitamin D that is produced is similar to the susceptibility of people to get sun burnt: in people with a pale skin and red hairs, the production of this vitamin is faster than in people with a very dark skin. These people must be extremely careful with skin cancer, but we can always follow certain measures in order to benefit from the sun without risks.
Nowadays, it is thought that the ability to produce vitamin D has been one of the decisive factors in the evolutionary development of pale skin. This theory states than humans have adapted in their migration to the northern areas in order to optimize the production of vitamin D.
How much sun is necessary to produce vitamin D?
These are the times that each skin tissue needs to produce 2.000 IU of vitamin D daily, during a sunny day, while laying down and with short clothing (arms and legs exposed) and without sunscreen.
If you are standing, walking, or running, the exposure time must be prolonged twice. This also applies to people with severe obesity or old people.
Type 1: people with pale skin and red hair
- From October to March: Not enough radiation
- From April to May: Morning (11-15) 10-20 minutes. Evening: 20-25 minutes
- From June to August: Morning (11-15) 5-10 minutes. Evening: 15-20 minutes
- September: Morning (11-15) 10-20 minutes. Evening: 20-25 minutes
Type 2: European (mainly from the north), blond, blue or green eyes, with freckles
- From October to March: Not enough radiation
- From April to May: Morning (11-15) 15-25 minutes. Evening: 25-40 minutes
- From June to August: Morning (11-15) 10-15 minutes. Evening: 15-20 minutes
- September: Morning (11-15) 15-25 minutes. Evening: 20-25 minutes
Type 3: mixed type, Europeans and the Mediterranean area, light brown hair or black, without freckles
- From October to March: Not enough radiation
- From April to May: Morning (11-15) 20-30 minutes. Evening: 25-40 minutes
- From June to August: Morning (11-15) 15-20 minutes. Evening: 25-40 minutes
- September: Morning (11-15) 20-30 minutes. Evening: 25-40 minutes
Type 4: dark skin, brown eyes, brown or black hair. Europeans and South Asia type
- From October to March: Not enough radiation
- From April to May: Morning (11-15) 30-40 minutes. Evening: 45-60 minutes
- From June to August: Morning (11-15) 10-20 minutes. Evening: 20-25 minutes
- September: Morning (11-15) 30-40 minutes. Evening: 45-60 minutes
Type 5: dark skin, black hair, people from North Africa, India, and Pakistan
- From October to March: Not enough radiation
- From April to May: Morning (11-15) 40-60 minutes. Evening: 60-90 minutes
- From June to August: Morning : 30-40 minutes
- September: Morning (11-15)40-60 minutes. Evening: 60-90 minutes
Type 6: dark or black skin, people from Central Africa and Asians with dark skin
- From October to March: Not enough radiation
- From April to May: Morning (11-15) 40-60 minutes. Evening: 60-90 minutes
- From June to August: Morning 30-40 minutes.
- September: Morning (11-15) 40-60 minutes. Evening: 60-90 minutes
Sun and vitamin D during old age
The ability of the organism to produce vitamin D through the skin is reduced with age, which is the reason why some old people often suffer a vitamin D deficiency.
At the age of 70, the ability of the skin tissue to carry out the synthesis of vitamin D is reduced approximately in a 75%.
This is due to the conditions of the dermis itself, as well as to the fact that the amount of 7-dehydrocholesterol diminishes drastically with age.
In spite of this limited capacity, the radiation of the sun is still the most important source of vitamin D for old people. However, it gets more difficult for the body to produce it, and vitamin D dietary supplements become indispensable during winter in order to keep adequate levels of vitamin D and to avoid an acute deficiency.
Vitamin D and the sunscreen
The UV radiation is important for the production of vitamin D and, therefore, for health. But paradoxically, it is also potentially harmful, since an excessive tan can lead to the premature aging of the skin tissue and to the development of skin cancer.
The information about this risk has been excessive, which has led many people to avoid sunbathing for the fear of developing cancer, and thus, to renounce to its positive effects.
This has also led many people to use a sunscreen with a very high protection factor. This filter prevents the wavelengths to go through the dermis to produce vitamin D in the organism.
With a level 8 protection factor vitamin D is no longer produced.
The problem with sunscreens
Apart from blocking the synthesis of vitamin D, sunscreens also have many negative side effects. The impregnation of the superior layers of the skin with chemical products reacts with the radiation of the sun and produce aggressive free radicals that attack the dermis cells and damage them. In this sense, the sunscreens that include chemical products such as titanium dioxide and zinc oxide are particularly harmful.
The chemical products that are included in the sunscreen also enter the bloodstream and affect the hormone balance. In general, they affect estrogens which are the female sexual hormones. These chemical substances can even affect breast milk and the development of the baby during lactation.
That is why, if you use sunscreen, you must make sure that its composition only includes natural products in order to reduce the negative side effects of the sunscreen as much as possible.
It is advisable to use clothes as the best way to protect ourselves from UV rays as much as possible.
Exaggerated fear to the sun
In normal circumstances, sunscreens are not necessary because the skin tissue already has an excellent protection against excessive exposure to radiation. The melanin from the skin, which is in charge of its tan, since it is an efficient protective factor against radiation.
The most important thing to protect ourselves from UV rays is the slow development of the pigmentation of the dermis. This must occur from the inside to the outside in several layers, so that the form of the superior layers of the dermis have enough melanin.
A slow and progressive exposure is the most efficient way of protecting the skin tissue. On the contrary, a too quick and intense exposure to radiation entails a big risk and can cause serious damage. A slow adaptation is the most important factor to protect the dermis from the sun.
With a slow exposure, the skin tissue has enough time to adapt to the effects of the UV rays, so that the sun does not produce any negative effect on the dermis.
The relation between radiation and skin cancer is produced when the radiation levels are high. With a slow and progressive exposure and a moderate tan, the benefits of the radiation are better for health than the possible harms. This does not solely affect to the production of vitamin D, since the sunlight has other positive physiological effects.
The warning against the impact of the afternoon radiation and the advise of using chemical sunscreens must be taken seriously, but we have to have a critical point of view as well, since everything comes to finding a balance, because avoiding to sunbathe does not allow the production of vitamin D, which leads to the development of several diseases.
What is the best way to sunbathe?
These are some key points to sunbathe optimally and to generate vitamin D in the organism:
1. Determine the individual protection in each case
Until the first sign of redness appears, the dermis is optimally protected against the harmful effects of the UV rays. This period is called minimum erythema dose (MED) and it must be individually determined, by observing the precise moment when the skin starts to redden after being exposed to the sun. The time we spend sunbathing without protection must not surpass a 50% of the MED period. The MED increases with the tan, according to each kind of skin.
2. Progressive exposure
The most advisable thing is to expose ourselves progressively to the radiation. We should start sunbathing from springs onward, if possible. The exposure to the sun must be short if it is without sunscreen. If it is only carried out during the weekends, we must not exceed the exposure time.
3. Sunbathe everyday
As long as the weather allows it, we should plan to sunbathe everyday, for a short time.
4. Sunbathe as most skin as possible
The tanning of the face and arms is not enough to produce vitamin D. The ideal thing is to sunbathe naked or wearing a swimsuit, if this is not possible, with shorts and a t-shirt.
5. Sunbathe carefully and without sunscreen
The first half of the MED period must be done without sunscreen. From that moment onward, you can already use a sunscreen or clothing to cover the body.
Vitamin D and winter
During the winter, in those areas situated to the North of Rome, the adequate intake of vitamin D can only be achieved in three ways:
- With the consumption of foods with vitamin D (fish, mushrooms)
- With the intake of vitamin D supplements
- Going to a solarium
The intake of foods to produce enough vitamin D involves a very unbalanced diet, similar to the “inuit” diet (native people from the Arctic). This diet cannot be followed by everyone and it is also problematic for vegetarians and vegans.
Vitamin D supplements are the easiest, most affordable, and safest way to satisfy the requirements of vitamin during winter. Nowadays, there also also products suitable for vegetarians and vegans.
The sun is our main source of vitamin D. We should sunbathe as much as possible during the summer, but always carefully.
In winter or when it is not possible to sunbathe due to the lifestyle or work hours, the vitamin D dietary supplements are the cheapest and most useful method to guarantee an adequate supply of vitamin D in the organism.
Vitamin D and the solarium
Vitamin D has a peculiar feature in regard to other vitamins, it is the only one that does not have to be absorbed through foods, rather it can be produced by the body when we sunbathe.
The production chain to generate vitamin D begins with 7-dehydrocholesterol cholesterol, which is found in the most superficial layer of the skin or epidermis.
This cholesterol absorbs the radiation of the sun with a wavelength of 290-315 mm, in other words, the UVB radiation range. By using UV radiation, cholesterol becomes pre-vitamin D, a precursor form of vitamin D. From then on, the heat of the UV radiation is necessary to carry out the next step, and to develop vitamin D.
An ingenious protection mechanism prevents us from producing too much vitamin D when we expose ourselves excessively to the sun. The body can produce until 20.000 IU of vitamin D, and when it reaches this limit, the vitamin D excess is decomposed in inactive photoproducts.
The vitamin D that is produced in the skin enters the blood and goes to the body’s tissues, where it is transformed into the vitamin D hormone calcitriol. Another part of the vitamin D deposit is transported to the kidney and the liver, where it is deposited and transformed into 25 (OH) D3. This is the most common form of vitamin D in the body, which is the also used to measure the levels of vitamin D in the organism.
A clinical study proved that going to a solarium regularly ensured stable levels of vitamin D 48 ng / ml, while the levels of the control group, which was made of people that did not go to the solarium, were reduced to a 14 ng / ml.
The vitamin D that is consumed through food can solve certain disorders, such as a bad absorption of fat, Crohn’s disease, cystic fibrosis, or a gastric bypass.
Can the solarium produce vitamin D?
The solarium was created to imitate the tanning that is produced by the sun. However, the solarium does not use the whole sunlight spectrum.
The solarium produces less UVB radiation than the sun, but it also generates vitamin D.
In order to compare the activity of the solarium with the power of the sun, we must measure it with the unit of sun radiation measure, MED, which is the minimum erythema dose.
MED is defined as the sunlight that is obtained during 30 minutes of exposure in Oslo, in a summer afternoon. MED produces an easily noticeable redness on the skin.
Those who would rather not be exposed to the sun can attend a 20 minutes solarium session in order to compensate. In this case, it would produce the same amount of vitamin D than the one resulting from sunlight exposure, approximately from 10.000 to 20.000 IU. This is the amount that must be produced between 2 and 3 times a week, in order to maintain an adequate level. Therefore, the solarium produces vitamin D, like the sun.
The solarium: is it healthy or dangerous?
The solarium poses a dilemma, while it can good in order to produce vitamin D which protects us from cancer, osteoporosis, Alzheimer’s disease, and other diseases, we should ask ourselves if it can cause skin cancer.
Even though the sunlight can be dangerous, the risk of developing skin cancer depends on the type of sunlight. The melanoma from skin cancer depends on the type of radiation that has been received. When it is a high intensity radiation, the risk of developing a malign melanoma increases.
This is why it is so important to avoid sun burns! However, a uniform and lower intensity exposure to the sun has a protective effect.
Let’s not forget that the sunlight is absolutely necessary to produce vitamin D. Moreover, the sun acts on the endorphins and serotonin, and produces wellbeing and a relaxing effect. That is why we must enjoy the sun, but always with care. We must sunbathe moderately so that the UV is beneficial for us, without being harmful or dangerous.
In the year 2011 a norm about solaria and UV ray protection was published, so that now they are equipped with softer mechanisms, whose light spectrum is closer to the one that is found in nature. The risks are lesser with a moderate use.
Is there a risk of developing cancer if we get tanned in the solarium?
For a long time, it was believed that the UVB radiation that causes skin rashes is the one responsible for the development of the malign melanoma skin cancer. This led to a reduction of the radiation in the solarium, with the objective to reduce the risk of suffering skin cancer.
The tan and pigmentation of the skin is achieved mainly through UVA radiation.
However, recent research has proven that the UVA wavelength radiation from tanning cabins can cause certain types of skin cancer, which questions directly the safety of solaria.
Some studies have addressed the topic of the risk of developing a skin cancer in tanning cabins, although their conclusions have never been concluding. However, there is evidence that the use of the solarium increases slightly the risk of suffering skin cancer. However, we must also weight this risk with the benefits that it produces when it comes to vitamin D. Once again, moderation is the key.
A revealing fact is the relation that exists between vitamin D and skin cancer. If the melanoma is diagnosed during the summer, its survival is higher than when it is produced in winter. The researchers suspect that this is due to the fact that higher levels of vitamin D during the summer offer a partial protection against skin cancer. According to this, the regular use of the solarium could provide this “summer protection” for the whole year due to a higher supply of vitamin D.
The disadvantage of the solarium consists on the fact that UVA radiation is that it can accelerate the aging of the skin. Those who want to avoid this and want to maintain optimal levels of vitamin D for the whole year can take a vitamin D nutritional supplement in bars, capsules, or drops.
The Intake of vitamin D through dietary supplements
The best choice to provide the requirements of vitamin D to the organism is to use dietary supplements. This is a safer option, specially in the cases of people that do not receive enough sunlight or who do not want to expose their skin to the sun. Vitamin D dietary supplements can be consumed in different formats: capsules, drops, or bars.
Who can benefit from the intake of vitamin D dietary supplements?
- Those with a vitamin D deficiency
- People who want to keep normal levels of vitamin D in blood 25 (OH)
- To prevent the development of osteoporosis (bone loss)
- Old people that already suffer from osteoporosis
- Those who are depressed
- To prevent rickets in children
- People with hypertension
- To prevent certain types of cancer, such as breast cancer, kidney cancer, or colon cancer.
- To prevent and treat respiratory infections
- To prevent against autoimmune diseases
Vitamin D3 or D2: which one is better?
Clinical studies have proven that vitamin D3 is much more effective than vitamin D2. The intake of vitamin D3 increase the levels of vitamin D in the organism.
Those who consume vitamin D3 obtain twice the level of vitamin D in their body when compared to those that consume vitamin D2.
To this day, it was believed that both forms of vitamin D were similar. However, the clinical tests have proven that vitamin D3 is much better.
The enrichment of foods with vitamin D
In the last few years, plenty of sellers from the nutrition industry have used vitamin D2 to enrich their products, believing that with this they would satisfy the daily requirements of their customers. However, the clinical studies haven proven that vitamin D3 is much more effective than vitamin D2.
The researchers warn that we should not underestimate the importance of vitamin D for the body. There are geographical areas where vitamin D cannot be produced because there is not enough sun radiation. That is why it must be administered through the diet or through dietary supplements.
However, the clinical studies have proven that vitamin D3 increases the levels of vitamin D in the organism more than twice. Those who consume foods with vitamin D3, such as fish, eggs, or vitamin D3 supplements, increase their vitamin D levels much more than those who consume food with vitamin D2, such as bread or milk enriched with vitamin D2 or vitamin D2 dietary supplements.
Nutritionists have claimed that this discovery will drastically change the field of health and nutrition industry. A vitamin D deficiency is a serious problem but, thanks to this discovery, people will be better informed about what they can do to increase their vitamin D levels.
How can we measure vitamin D3 levels
The only way to measure the levels of vitamin D is by carrying out a blood test. This does not measure the active form of vitamin D, but rather the concentration of 25(OH)D (25 hydroxyvitamin D) in the blood.
The value 25 (OH) D is a precursor form of the vitamin D that is transported in the blood. This levels is transformed into the active form of vitamin D (calcitriol).
This shows the supply of vitamin D that the organism has when the test is carried out, but it does not provide any information about the origin of this supply. This means that there is no way to know is it has been obtained through sunlight exposure, nutrition, or the intake of dietary supplements.
The lifespan of 25 (OH) is of approximately two months. Once this time has passed, the level is reduced to a half, as long as we have not received a new supply of vitamin D.
What is the optimal level of 25 (OH)
Nobody can claim with certainty which is the optimal level of 25 (OH) D. In general, there are different types of recommendations. Analyzing the most frequent ones, we have reached the following conclusion:
- A vitamin D deficiency occurs with levels under 20 ng/ml, and there is a risk of suffering from rickets, osteoporosis, and a calcium deficiency.
- A level between 21 – 40 ng/ml, is adequate, however, it can develop symptoms of a deficiency in the long term.
- A the level is between 41 to 60 ng/ml is an optimal supply in order to maintain our health.
- Between 61 to 80 ng/ml moves between normal to high levels of vitamin D, still within the normal range.
- Between 81 to 100 ng/ml, the values are slightly higher than normal, but it does not entail any risk for health. Generally, these levels are only obtained through vitamin D dietary supplements.
- Between 101 to 150 ng/ml, there is an excess of vitamin D, but these values are not harmful.
- If the values are over 151 ng/ml, there is an intoxication of vitamin D, so its consumption must be stopped immediately and avoid exposure to the sun.
- If the value surpasses the 280 ng/ml it can trigger a disorder of the calcium metabolism.
Those who live in Southern countries spend a lot of time exposed to the sun and, quite often, they tend to reach levels of 100 ng/ml or more, but they do no present sign of an overdose. People with dark skin need from 5 to 10 times more tanning than fair-skinned people in order to produce the same amount of vitamin D.
The levels of vitamin D can change a lot from one person to another
The ability to increase the levels of vitamin D through exposure to the sun or using supplementation varies considerably from one person to another and depends on many factors. Between them we include age, body weight, skin color, intensity of the exposure, lifestyle, particular levels of vitamin D, and the ability of the organism to absorb it.
This means that not all people can reach or maintain the same 25 (OH) value by consuming the same dose of vitamin D.
Therefore, the recommended steps to measure the optimal dose are only an approximation.
What is the difference between a 25 (OH) D value in ng/ml or in nmol/l?
Normally, in Europe, the 25 (OH) D value is given in ng/ml. But in some laboratories they also give this value in nmol/l.
- In order to transform the result of a test in nmol/l into a value of the unit of measure ng/ml, the value nmol/l has to be divided in 2.5. For example, 50 nmol/l equals 20 ng/ml (50 ÷ 2.5).
- In order to transform the result of a test in ng/ml into a value of the unit of measure nmol/l, the value ng/ml must be multiplied by 2.5. For example, 20 ng/ml equals 50 nmol/l (20 x 2.5)
Vitamin D capsules, vitamin D tablets, or vitamin D drops, which format is the best?
If you want to buy vitamin D supplements you can find them in different formats: in capsules, tablets, or drops.
Vitamin D capsules
The vitamin D capsules are filled with a little bit of powder, unlike tablets, they do not undergo a high pressure process, which means that they dissolve completely in the stomach if a few minutes. This guarantees a quick absorption of the vitamin D3.
When you buy capsules, make sure that they do not have any additive, color, or any other added product, such as lactose.
The capsules tend to be quite small. However, there are some people that cannot swallow them. In this case, we can open the capsule and consume the content directly with a spoon.
Vitamin D tablets
Another one of the most common formats are tablets. However, tablets contain unwanted additives, such as magnesium stereate, silica, sucrose, talcum, etc.
Vitamin D drops
Vitamin D drops only have vitamin D oil. It is an oil made of olive oil, coconut oil, hemp oil, thistle oil, or sunflower oil, and vitamin E as an antioxidant element. Sometimes it is added fruit flavor in order to improve the result. However, this is not necessary since the oil has a neutral flavor even though it is fatty oil.
The drops allows to get the perfect dose, according to individual requirements. They tend to be available in doses between 200 IU to 5000 IU per drop.
Vitamin D softgels or soft capsules
The soft gelatin capsules are filled with vitamin D oil, and they are relatively easy to swallow. The gelatin capsules do not normally have unnecessary additives. The part that covers the capsule is usually made of gelatin, which is the reason it cannot be consumed by vegetarians nor vegans.
Vitamin D sticks
The vitamin D sticks are very practical because they can be consumed anywhere. They are also available in different flavors, which is the reason why they are the favorite format among children. On the other hand, we must always read the ingredients list to see if they have unwanted additives.
Vitamin D sticks are more expensive than other vitamin D formats due to the number of portions per package.
Vitamin D bars
The vitamin D bars are quite useful, since they can be comfortably carried around everywhere you go. Moreover, there are different flavors available, which is the reason they can be easily consumed by children. However, the bars can have unwanted additives, caking agents, and flavorings. This is why it is recommended to read the composition previously.
Moreover, the bars are more expensive than other supplements due to the packaging that each portion requires.
Combined preparations of vitamin D and K2
If you usually consume vitamin D supplements, you should also use vitamin K2 in order to guarantee the absorption of calcium by the vitamin D that is stored in the bones and that it does not deposit in the arteries, where they can cause arteriosclerosis.
The best choice will always be to combine vitamin D and K2. When we select this product you have to know that vitamin D is naturally found in lanolin or lichens, along with natural vitamin K2 as MK7, made of natto.
How to combine Vitamin D with Vitamin K correctly
Recent research has clearly proven that both vitamin D3 and vitamin K2 are crucial to maintain a proper state of health. Nowadays, vitamins deficiencies are quite widespread, since more and more people use vitamin D3 and K2 dietary supplements daily.
The key lies in knowing that vitamin K2 must be consumed along with vitamin D3.
This may raise the question about how should they be optimally combined in order to favor the best state of health and vitality.
Vitamin D and vitamin K only work optimally when they are consumed together
Those who regularly use a vitamin D dietary supplement, must additionally consume vitamin K2. This vitamin has the important task of leading calcium to the correct areas of the body, so that they strengthen the bones and teeth. At the same time, it prevents calcification, since calcium can be deposited in places we do not want to, such as the arteries and other soft tissues of the body.
When we decide to consume Vitamin D, it is recommended to know that an adequate amount of Vitamin K2 is needed in the organism, since they work together when it comes to the absorption of calcium, more specifically, it is in charge of fixing it to the correct place in the body. This avoids the diversion of the mineral to other areas which would cause calcification or kidney stones.
This means that the vitamin D needs the help of vitamin K2. Both vitamins work together in order to strengthen the bones and health of the heart and arteries.
Optimal dose of vitamin K2
The vitamin K is only produced in the large intestine in little amounts. This is the reason we must consume it though foods or dietary supplements that are rich in vitamin K. Occidental people clearly suffer from a deficiency of vitamin K.
People over 50 particularly undergo a greater risk, specially when it comes to cardiovascular diseases and osteoporosis. Nowadays, there are less foods that have vitamin D and the exposure to the sun is very limited, which lead the organism to a lack of this element.
Professor Vermeer, from the University of Maastricht, advises a dose between 100 and 200 micrograms of vitamin K2 per day. The highest dose, 200 mcg, is recommended specially for individuals that have a family history of cardiovascular diseases or osteoporosis.
Those who experience early symptoms of a cardiovascular disease or osteoporosis can also consume the highest dose in order to make sure that all the type Gla proteins (MGP) will be activated in the body.
Generally, consuming 45 micrograms of vitamin K2 daily should be enough. For healthy people under the age of 50, this recommendation is only valid if an additional vitamin D3 dietary supplement is not being used.
But you should consume at least 100 micrograms if you want an optimal supply that guarantees that all the proteins that depend on vitamin K2 activate in the body.
This recommendation of the vitamin K2 intake is applied both if you are consuming vitamin D3 or not. This means that even if you are consuming a vitamin D supplement, you must also follow the dose of vitamin K2 that has been described.
Note: if you are using anti-coagulants you must consult your doctor before using vitamin K2. This is because the intake of vitamin K2 can reduce the effect of anti-coagulant medicines based in coumarin, such as warfarin.
Since our bodies necessarily require vitamin K in order to maintain the health of the bones and arteries, it is advisable to use anticoagulant medicines that do not inhibit vitamin K. Talk to your doctor so that you can get an anticoagulant that acts independently from vitamin K.
If this is not possible, you can still consume 45 micrograms of vitamin K. Research has proven that this amount does not affect the effect of anti-coagulant medicines, and it is completely safe.
We suggest the following doses of vitamin K2:
45 micrograms of vitamin K2 daily:
- If you are using anti-coagulants
- Consume carefully if you are under 50 years of age and do not consume additional vitamin D
100 micrograms of vitamin K2 daily:
- In the case of healthy people under 50 years of age that do not consume additional vitamin D
- In the case of those that consume up to 2.500 IU of vitamin D daily
200 micrograms of vitamin K2 daily:
- People with a family history of cardiovascular diseases or osteoporosis
- People with early symtpoms of a cardiovascular disease or osteoporosis
- People who consume more than 2.500 IU of vitamin daily
How to combine vitamin D3 with vitamin K2?
We recommend that you consume vitamin K2 for the entire year in the optimal dose for you (as it was previously described). You must adjust the vitamin D dose to your lifestyle or, even better, to your D3-25 (OH) blood test.
This means that if you sunbathe during the summer more than twice a week, it is quite possible that at that time you do not need to consume additional vitamin D3. During the rest of the year, the experts recommend to adapt the vitamin D dose to your lifestyle and age, which means that you need to adjust the dose so that the 25(OH)D are situated on an optimal range from 50 to 80 ng/ml.
Depending on the season, a dose of vitamin D3 between 2500-5000 IU is optimal to maintain a healthy level of 25(OH)D and 50-60 ng/ml in the blood for most people.
Vitamin D and vitamin K2 work independently. This means that no matter the amount of vitamin D you are consuming, if you use the optimal dose of vitamin K2, between 100 to 200 micrograms daily, you will still benefit from its effects (see details above).
Note: It is advisable to test the 25(OH)D in blood every three months if you regularly consume a dose of 5000 IU daily. This test allows you to determine the exact amount of vitamin D3 that you must consume daily in order to get the optimal levels of vitamin D3 in the organism.
How does vitamin K2 work?
Vitamin K2 has been scientifically studied for several years. But its importance for health has been discovered due to the impressive studies carried out by the University of Maastricht, which has drawn a lot of focus to vitamin K2.
Vitamin K2 is in charge of controlling the way calcium is stored and used by the organism. The process is carried out through Gla proteins that depend on vitamin K2, since it is the only one that can activate them.
Although vitamin D is the one in charge of the production of osteocalcin, it can only be activated through vitamin K2 that leads this protein to the bones.
Vitamin K2 activates the Gla protein (MGP), which is in charge of regulating calcium in the walls of the arteries. The MGP is the most efficient inhibiting factor against atherosclerosis and can only be activated by vitamin K2. A vitamin K2 deficiency inevitably produces the hardening of the arteries.
Without the activation of the Gla protein, calcium wanders uncontrolled in the arteries and produces atherosclerosis. Moreover, the calcium that is absorbed through the intake of vitamin D through food will wander through the organism if there is not enough vitamin K2, it will deposit in the soft tissues of the body and in the arteries, producing atherosclerosis.
This is the reason why vitamin D3 must be always consumed along with vitamin K2. These two vitamins work together synergistically and store the calcium in the bones, avoiding the risk that its deposit in the arteries would entail.
Conversion of vitamin D: from mcg to IU
The conversion rate is 1:40. According to this, 1 mcg (micrograms) of vitamin D equals 40 IU (international units).
These are some examples:
- 5 mcg of vitamin D equal 200 IU
- 25 mcg equal 1.000 IU
- 125 mcg equal 5.000 IU
- 250 mcg equal 10.000 IU
What is vitamin D made of?
Vitamin D has two different forms:
- As vitamin D3 (colecalciferol)
- As vitamin D2 (ergocalciferol)
It is regarded as the active form of vitamin D and, therefore, it is included in most of the supplements that are available in the market.
Vitamin D3 is generally obtained from lanolin (fat from sheep’s wool). It can also be obtained from cod liver oil. In this case, it must be pointed out in the label.
If the label says that the vitamin D3 has colecalciferol, it will generally come from lanolin and it is regarded as vegetarian (although not vegan), since the animal has not been harmed, rather, the wool is obtained from the shorn.
Vitamin D3 has been recently obtained from lichens, which means that is suitable for vegans.
This vegan vitamin D is as valuable as vitamin D3. It is very appreciated by the vegans, since now they have an alternative to vitamin D2.
A vitamin D3 supplement is regarded as the superior form of vitamin D. Research has proven that it is 1.7 times more efficient than vitamin D2 when it comes to increasing the level of vitamin D 25 (OH) in the organism.
It is mainly found it certain types of mushrooms in the form of ergosterol, and it has the function of the provitamin D. Under the influence of the UV rays, vitamin D2 (ergocalciferol) is produced in the skin.
Vitamin D and the immune system
Vitamin D has an essential function for health, since it protects from many diseases, such as osteoporosis, respiratory tract diseases, Alzheimer’s disease, chronic inflammation, and cancer.
Vitamin D acts in two ways: as an immune defense at a general level and as a specific defense, acquired or adaptive immunity. Both functions are combined to protect the body from viruses, bacteria, fungi, and other pathogens.
This great versatility is is due to the fact that each cell of our body has the ability to produce vitamin D. They only need to receive enough sunlight and UVB radiation. In the northern geographical areas there is not enough sunlight in order to produce vitamin D in a proper way. In this case, vitamin D supplements are the solution to the problem.
A first sign of the cooperation between vitamin D and the immune system is manifested in the ability of each immune cell to produce vitamin D, apart from the fact that each cell has a vitamin D receptor on their surface. Therefore, cells use it to exchange information in order to activate an immune defense that is as wide as possible.
Vitamin D and the innate immune system
The innate immune system responds with a quick defense against the invasion of all kinds of pathogens, such as the bacteria that enter the wounds or the mucous membranes. Therefore, the innate immune response is general and efficient against a wide range of germs. This reaction is produced locally and in a short period of time, for example, the bacteria from wounds are spotted and defeated in a matter of hours.
Within the innate immune system there are external barriers formed by the skin and the mucous membranes, certain white cells (leukocytes), several substances in the blood and other bodily fluids. When the bacteria and viruses enter the body, they can be eliminated by the phagocytes along with the acquired immune system, among which are included the macrophages from tissues and the neutrophil granulocytes from the blood and tissues.
The role of vitamin D in the innate immune system has been studied for more than 30 years, due to the discovery that it is necessary for the maturing of macrophages. When the immune system is attacked, vitamin D activates said phagocytes in order to decompose and eliminate the bacteria through the cell elimination system.
The key role of vitamin D to coordinate the defense of the innate immune system
The immune cells are activated when they link to the vitamin D receptors (VDR) on the surface of the cells. They directly regulate DNA through this link. In a laboratory study, it has been discovered that vitamin D activates 291 genes that are situated in the white cells from the immune system.
These genes are stimulated by vitamin D in order to produce important proteins and peptides (very short proteins) that act as a defense of the immune system when it is attacked. This is where the importance of vitamin D gains relevance within the immune system.
Vitamin D and the acquired or adaptive immune system
Unlike the innate immune system, the acquired or adaptive immune system acts in the long-term. After repelling an attack, the adaptive immune system forms specific antibodies that will remember the antigens, such as viruses. Due to this specialty, the immune response is slower and it takes a few days to react. This pathogen is stored in the immune memory and, later on, a similar attack will be harmless.
Among the main components of the adaptive immune system we can find especial white cells, called lymphocytes B and lymphocytes T. They are soluble protein bodies in the blood that activate the immune system through specific messengers, called Cytokine. The lymphocytes B are in charge of the specific production of antibodies and lymphocytes T destroy and eliminate the pathogen agents.
Vitamin D maintains the functioning of the immune system’s memory
Vitamin D regulates several components of the immune system. When detailed blood tests were compared to the level of vitamin D, it was discovered that the memory of vitamin D activates the functioning of the cells, which helps to increase the innate immune memory.
Moreover, it also plays an essential role in the adaptive immune system. The factors that relieve inflammation are accelerated to relieve the immune system, and they also activate cytokines even more, which actively fight against inflammation.
Therefore, vitamin D has a holistic effects on the immune system and regulates almost all its defensive aspects when facing the attack of a pathogen agent. This underlines the enormous influence that vitamin D has in order to keep the immune system healthy. A vitamin D deficiency in the organism results in a weak immune system, a higher risk of suffering diseases and a longer treatment. Vitamin D supplements strengthen the two essential aspects of the immune system, the innate and the adaptive.
Vitamin D and autoimmune diseases
Due to the essential role of vitamin D in order to regulate the immune system, it is easy to understand its importance for autoimmune diseases.
The clinical studies have proven that low vitamin D levels are closely linked to the development of several diseases, such as rheumatism, Crohn’s diseases, multiple sclerosis, and diabetes.
The intake of vitamin D and its production through sun exposure can also affect the development and gravity of the disease. The gene alterations on the part of DNA that codes the vitamin D receptors in the cell’s surface are also involved in the risk of suffering an autoimmune disease.
The first tests that have used vitamin D as a treatment for autoimmune diseases have provided extremely positive results. In the laboratory, it was possible to absolutely prevent the development of multiple sclerosis in mice through the supply of vitamin D for two weeks. The long-term studies in humans are not concluding yet, and scientists are trying to find out if the intake of vitamin D can change the course of autoimmune diseases.
To sum up, vitamin D is absolutely necessary for the optimal functioning of the immune system. Its deficiency affects the immune system and slows it down, which reduces the protection of the organism against the attack of pathogen agents such as bacteria and viruses.
Therefore, we must maintain high levels of vitamin D for the whole year, not only during the summer. The optimal levels strengthen the body during the winter and protects it from suffering the flu and colds. Moreover, they help with the prevention of the development of autoimmune diseases and to mitigate their symptoms.
Vitamin D and osteoporosis
Did you know that you can suffer osteomalacia (softening of the bones) and osteoporosis even if you have an adequate intake of calcium? The reason is a lack of vitamin D, since it is the one in charge of the absorption of calcium and phosphorus in the intestine, as well as of depositing calcium in the bones.
Moreover, vitamin D prevents the kidney from excreting too much calcium. On the other hand, it also regulates the metabolism of calcium along with vitamin K, and prevents the development of rickets in children and bone weakness in adults. All in all, it improves the health and the structure of the bones and prevents the development of osteoporosis in old people.
If the levels of vitamin D are too low (under a 25 (OH) value, the intestine cannot absorb enough calcium. Consequently, there is a very little amount of calcium that can be stored in the bones to keep them strong. The bones release calcium to maintain a constant level in blood. Old people, poorly fed, and with little exposure to the sun will suffer from osteoporosis sooner or later.
A 99% of the calcium is used to strengthen the bones and teeth. But the rest of the percentage is absolutely necessary for the transmission of stimulus between the nerve and brain cells, the coordination of the muscles, the transmission of information between the hormones, the functioning of the growth hormones and the neurotransmitters, which produce calmness and wellbeing.
The terrible statistics about osteoporosis
Every three women and men over the age of fifty have symptoms of osteoporosis. Two hundred and fifty millions of people around the whole world suffer bone loss. In fact, this is the most common cause of bone fracture in people over the age of 65.
The population of old people constantly grows, which is the reason why osteoporosis has become a serious sanitary problem. An adequate prevention by consuming enough vitamin D and calcium could avoid a lot of suffering, prolong life, and reduce the sanitary costs.
Most of the patients that suffer from osteoporosis have a low level of vitamin D. Around 40% of the patients that suffer pelvic fractures have a massive deficiency. Most of those who are affected also have a low level of calcium. In a double blind study, controlled with placebo, it was proven that consuming calcium daily and 800 IU of vitamin D3 increased bone density and reduced, up to a 43%, the risk of suffering a hip fracture.
Between a one and two per cent of the bone mass is lost each year, which is the reason why it is necessary to have a proper supply of vitamin D, vitamin K, and calcium. The symptoms of osteoporosis can take between ten and twenty years to appear, which is why we must worry about receiving enough sunlight in our skin regularly, or consuming a vitamin D dietary supplement.
Vitamin D and depression
With the coming of winter, the days are shorter, the sky is gray, and the sun barely appears. This tends to trigger the typical winter depression. From a medical point of view, this depression is similar to SAD (“seasonal affective disorder”), which is more pronounced and affects to approximately 1 to 3% of the European population.
One of the causes of SAD is a vitamin D deficiency. A continuous deficiency triggers the typical winter depression, which is harmless, but it can produce a more serious depression, accompanied by symptoms of apathy, sleep disorders, sadness, guilt, and a lack of motivation.
Normally, the symptoms disappear after a while, but it is recommended to consult your doctor if they persist. The treatments with soft medicines, accompanied by an increase of the intake of vitamin D and serotonin can calm the most mild depressions.
The connection between vitamin D and depression
For many years, the positive effect that sunlight has at a psychological level has been known. However, the concrete process that produces it is ignored. One of the most important tasks of the sunlight for the human body is the production of vitamin D, which is only produced through UVB radiation. When there is not enough sunlight, the solution consists on getting its supply through the diet or by consuming a higher dose of dietary supplements.
A lack of vitamin D is linked to the seasonal depression and with other more serious forms of depression, according to the clinical studies carried out in the last 15 years. According to these studies, all those people who suffer from some kind of depression have low levels of vitamin D.
The use of vitamin D to stop depression
Vitamin D is being studied in depth in order to discover its efficacy in order to avoid or stop depression. When vitamin D is formed in the body, it is attached to the specific receptors that the cells have on their surface, it is absorbed and enters the cell, regulating the activity of certain genes.
Vitamin D is very active, specially in the brain, and its activity is similar to that of neurosteroids.
The neurosteroids are messenger substances that are formed and act directly in the brain. This means that they do not have to be transported. They act quickly and efficiently because of this. The neurosteroids regulate the functioning of dopamine and serotonin, by forming a neuro-chemical base of psycho-physiological states, such as stress, anxiety, and depression.
The researchers have reached the conclusion that vitamin D has very similar functions to those of neurosteroids, which could explain why the cases of deficiency end up in depression.
Can vitamin D prevent the development of depression?
Even though it is known that there is a direct relation between a vitamin D deficiency and depression, there is still not concluding evidence that explains the reason of this correlation.
Researchers have carried out a study on postpartum depression and they have discovered that the daily intake of 2.000 IU during the last three months of pregnancy reduces the probability of suffering from depression.
This study has confirmed that the vitamin D deficiency is involved in the development of postpartum depression, and that the increase of the vitamin D levels through the consumption of supplements reduces the risk of developing a depression.
All in all, the clinical studies prove that vitamin D is important to maintain the brain and the state of mind in optimal conditions and that its deficiency can produce depression.
Vitamin D and inflammation
Vitamin D performs several tasks in the body, and it is renowned for its influence in order to maintain strong and stable bones and to prevent osteoporosis.
However, the vitamin D also helps to calm the inflammation. This is done through several interactions with the immune system, to which it actively helps to fight viruses, bacteria, and other pathogens.
When facing an attack to the immune system, vitamin D activates especial anti-microbial mechanisms that inhibit the inflammation. Due to this, it performs a decisive task in the prevention of acute or chronic inflammation and in the acceleration of the healing process.
Vitamin D as a substitute of antibiotics
The action of vitamin D to prevent inflammation and infectious diseases is not a new discovery. One of the first clinical studies, carried out in 1848, proved that the cod liver oil has a high concentration of vitamin D, thanks to which it was used to reduce the mortality rate in patients who suffered from tuberculosis.
Moreover, the Medicine Nobel Prize, Niels Finsen, discovered that the therapy through radiation worked to treat lupus vulgaris, a form of tuberculosis of the skin. The active element of this therapy was the UVB radiation from the sun that generates vitamin D. It was used to stop the tuberculosis that devastated Europe at the end of the 19th century and the beginning of the 20th.
Now, there is a growing interest in vitamin D to combat inflammation in a more efficient way than antibiotics. Even though right now tuberculosis is not regarded as epidemic, it still causes up to 1.5 millions of death every year in the world.
Does vitamin D help to prevent the inflammation?
The preventive use of vitamin D is, without any doubt, the most efficient method to combat inflammation. A great variety of clinical studies have proven that people with adequate levels of vitamin D have less probabilities of developing respiratory diseases, pneumonia, flu, ear infections, genital-urinary, and other infections, and they equally have a lower risk of suffering a hospital infection after a surgery.
These studies approach the topic from a retrospective point of view, which means that its concentration in blood is compared to the later infection. In all these cases, it has been proven that the vitamin D levels were insufficient (60 ng/ml). These results prove that an adequate supply of vitamin D provides protection from the infection and inflammation.
According to these studies, the researchers have reached the conclusion that plenty of infections, such as the flu and tuberculosis, are developed more frequently during the months of winter, when there is less sun and we have a lower level of vitamin D available, which makes us vulnerable when facing viruses and bacteria.
Does vitamin D help to cure inflammation?
The question whether if the intake of vitamin D can stop infections that are completely developed has been documented in the clinical studies on patients with tuberculosis, but it is still a controversial topic.
A more cautious response and, presumably, more accurate would be to think that the vitamin D helps the immune system to defend the organism from the inflammation. The last studies have been carried out in patients with HIV. After measuring the levels of vitamin D of these patients, a series of inflammatory markers were compared. It was proven that those patients with low levels of vitamin D presented significantly higher concentrations of interleukins and other factors, which suggest a higher activity of the immune system.
This means that vitamin D helps the immune system and makes it more efficient, even in the case of such an aggressive attack as the HIV virus. Unfortunately, vitamin D cannot heal the HIV infection, but it should be included in the search for the cure against HIV and other viral infections.
It is not always possible to remain a lot of time under the sun, which means that the best alternative consists on consuming vitamin supplements that help to compensate for the lack of sunlight and they increase the levels of vitamin D.
How to use vitamin D to treat inflammation?
The exact amount of vitamin D that is necessary to calm the inflammation is unknown. What is clear, however, is that the recommended level must not be lower than 40 ng/ml, specially in the months without sun. It is recommended to consume at least, 1000 IU daily in order to increase the levels of vitamin D from 40 to 80 ng/ml. The supplements offer a very simple alternative to be prepared and counter the next flu.
A meta-analysis of all the published studies on the matter, the conclusion was reached that it is more efficient to consume vitamin D daily and regularly, than consuming big amounts at a specific times, in order to protect ourselves from acute respiratory diseases. In the case of suffering acute and chronic inflammation, it is recommended to use vitamin D as well in order to help the immune system and to reduce the development of the disease.
Alternative uses of vitamin D to treat inflammation
An alternative administration of vitamin D has been tested in women with recurring chronic cervical inflammation. In the so called “problematic patients” that frequently suffer relapses even four times a year, and who have abnormal smears, a treatment was used that involved the administration of buffer solutions with olive oil and vitamin D.
After this treatment, almost half of the patients have experienced, after eight weeks, an improvement of the symptoms and a reduction of the inflammation.
However, before using this alternative method, you should consult your doctor.
The intake of vitamin D is recommended in order to prevent and treat inflammation and infectious diseases. If the intake of vitamin supplements is completely safe, the alternative methods of administration must be applied only under medical supervision.
Vitamin D and Alzheimer’s disease
Alzheimer’s disease is an irreversible neurocognitive disorder that leads to a loss of memory and perception, as well as behavioral changes. Alzheimer is the most common type of dementia.
The clinical research has recently proven that the risk of suffering Alzheimer’s disease increases significantly when there is a low level of vitamin D. This is due to the protective and healthy effect it has on the brain, since vitamin D guarantees the communication between nerve cells and, therefore, protects them from dying in the long-term.
How does the Alzheimer’s disease develop?
The nerve cells in the brain communicate through messaging substances. This communication is the base for the proper functioning of the brain, and it is what allows us to breathe, blink, remember, or dream. The nerve cells must be healthy and operating so that the system functions without any problems.
In the brains of patients that suffer from Alzheimer’s disease, the nerve cells, also called neurons, are damaged and die. This is due to the accumulation of abnormally folded proteins that are added to insoluble plaques between the cells and interfere in the normal communication. Other proteins (tau proteins) form fibrils, strands of fiber that are strongly twisted inside the nerve cells and block the supply of nutrients to the nerve cells.
Neurons cannot counter and stop these attacks. For a while, other neurons can perform the tasks of dead nerve cells and compensate for their death, but when there is a significant loss of nerve cells this compensation is no longer possible and other symptoms appear that are typical of Alzheimer’s disease.
Can Alzheimer’s disease be cured?
Nowadays, there is no known cure for Alzheimer. There are some medicines that compensate the neuronal death cause by the fluctuations of the messaging substances in the brain, but just for a while. The medicines lose their efficiency in one or to years (at most).
Can we prevent Alzheimer’s disease?
The researchers wonder why some people suffer from Alzheimer’s disease and others don’t. There is evidence that people with a bigger cognitive ability have less probabilities of developing Alzheimer’s disease.
Among the cognitive abilities are included memory, learning, and perception. The environment and the diet can be another risk factor to develop Alzheimer’s disease.
Certain vitamins, such as D, also play an important role, which could be crucial for the prevention of Alzheimer’s disease.
Vitamin D and its function in the brain
The precursor form of vitamin D, 25-hydroxyvitamin D, is produced in many regions and cells of the brain. This already points to the importance of vitamin D for the brain. The key factor for the Alzheimer’s disease is the neuroprotective effect of vitamin D, which could protect the nerve cells from dying.
We know that vitamin D is involved in the regulation of many genes which are responsible of the communication between nerve cells. Moreover, it also intervenes in the production of several neuroprotective substances, such as the neuron growth factors NGC and neurotrophin 3, as well as the choline acetyltransferase enzyme. This last one seems to perform a particularly important task in the development of the Alzheimer’s disease.
Acetylcholine is a neuron messenger which is not available in sufficient amounts in Alzheimer patients, due to the death of the neurons. This interferes in the communication between nerve cells and, at the same time, leads to the symptoms we know, such as memory loss and limited memory.
Is there any relation between the levels of vitamin D and Alzheimer’s disease?
Several studies have established a clear link between vitamin D and Alzheimer.
A meta-analysis of 37 scientific studies confirms that a low level of vitamin D in the blood is associated to a lesser cognitive capacity and to a higher risk of suffering Alzheimer’s disease.
This has been demonstrated in a study that was recently carried out on 1.658 old people during a period of 6 years.
This study ended a scientific controversy about if the existence of this deficiency was the cause or the result of the deterioration of the memory. The fact that all the participants were at the same cognitive level at the beginning of the study clearly showed that the deficiency of vitamin D favors the development of dementia or its progression.
Vitamin D to treat Alzheimer’s disease efficiently
A vitamin D deficiency is associated to a higher risk of suffering Alzheimer’s disease, this is due to the different function that vitamin D performs and that protect us against Alzheimer, for example:
- Helps with the production and the function of neuronal growth and stabilizes the affected nerve cells.
- Regulates an enzyme that is necessary to produce the acetylcholine messenger. A reduction of acetylcholine leads to the typical memory loss of Alzheimer’s disease.
- It suppresses the production of the amyloid precursor protein, which is in charge of the formation of the Aß plaques.
There was still a final test to measure the capacity of vitamin D to combat Alzheimer’s disease in patients that already had this disease. This important piece of the puzzle has been completed with a pilot study on 43 Alzheimer patients. All the patients have been diagnosed recently, and they did not use any medicine nor vitamin D before the study. They were given the Memantine medicine alone or combined with vitamin D, for a period of 6 months.
The results have been clearly proven in the group who was given the combination of medicine and vitamin D, whose cognitive performance increased, while the other group that only consumed the medicine did not show any change. This important study proves that vitamin D contributes to improving the memory of Alzheimer patients.
Vitamin D and sports
Russian and German athletes have used, for the last 30 to 40 years, the benefits of the sun to improve their physical performance. Moreover, it has been proven that sun exposure reduces the pain and encourages the healing of sport injuries. Trainers have always been convinced that the sun increases the strength, speed, and endurance.
The explanation about the properties of the sun to improve the sport performance lies on the fact that the sun contributes to producing vitamin D.
It has been proven that a 90% of the vitamin D is produced directly in the body by using the UVB sun radiation, and that only the remaining 10% is produced through the diet.
The importance of vitamin D for building muscle
When we practice sports, we undergo new challenges in order to constantly improve. The vitamins help us to achieve our objectives and to obtain a better performance.
The evidence of the link between vitamin D and muscle toning comes from the observation of age-related sarcopenia which produces the loss of muscle mass, weakness, and muscle pain. If the level of vitamin D is too low, there is a high probability of suffering sarcopenia.
A clinical study on old women showed that the intake of vitamin D favors muscle building even at old age. The women who received vitamin D showed a significantly improved performance than the participants on the control group.
According to other studies carried on adolescent girls, vitamin D also helps to develop the muscle in this case. Here, the level of vitamin that was measured in the blood was directly related to muscle performance and speed.
Vitamin D, the “legal doping” among athletes
The properties of vitamin D to improve performance had spread in the world of sports, and it is already being used by professional athletes. Foe example, not a single one Hockey player of the American National League has a vitamin D deficiency.
Professional football players also know that a high level of vitamin D increases muscle performance and physical endurance.
A meta-analysis of all the studies carried on the effects of vitamin D on adults (up to 40 years) has proven that “consuming vitamin D improves the muscle strength, both in the lower and upper extremities”. This means that the strength of the arms and legs of the athletes can be increased with the consumption of vitamin D.
How does vitamin D help to develop the muscle and achieve a better performance?
The exact function of vitamin D in building muscle and its optimal functioning is not clear yet, even though there is some evidence about the relation that exists between the two.
The exams of muscle tissue in patients with a serious vitamin D deficiency show that the muscle breakdown particularly affects type II muscle fibers, which are the ones of quick contraction. These muscle fibers are in charge of the quick performance of the muscle and, in old people, it also prevents falls.
At a molecular level, vitamin D links to a vitamin D receptor in the surface of the muscle cells, which regulates the calcium balance and the muscle function. In a clinical study carried out on mice, the deactivation of the vitamin D receptor in the muscle caused a lower performance when swimming. This proves that vitamin D performs a key role in the development of the muscles and, particularly, in the formation of type II muscle fibers.
The double support of vitamin D in sports
Apart from encouraging muscle performance and endurance, vitamin D also helps the immune system to control inflammation, which favors the sport performance.
Intense workouts and competitions tend to produce microscopic injuries and inflammatory processes, which is why the body must regenerate after the physical activity.
The anti-inflammatory properties of vitamin D helps the body to accelerate its regeneration after practicing sports.
Therefore, vitamin D favors the sport performance, muscle regeneration, and physical endurance.
One of the basic functions of vitamin D is to help with the development of muscle tissue, which facilitates a quick contraction. Indirectly, vitamin D also contributes to a faster recovery of the muscle. For all of this, we can claim that sportspeople and those who practice sports need to have enough vitamin D in order to improve their physical performance.
Vitamin D and testosterone
Testosterone is the main male hormone and it is in charge of the primary and secondary sexual impulses, mood swings, the accumulation of muscle mass, the formation of red cells and bones, as well as of the sexual functions.
Women also produce testosterone, but a 20% less than men. The hormones are mainly produced in the brain and the glands. In the case of the male testosterone, it can also be produced in the testicles. Male testosterone, like female estrogens, is produced through the transformation of cholesterol.
Clinical research has proven that vitamin D has an important role, since it regulates the functioning of the brain and the secretion of hormones. The clinical studies that have been carried out suggest that vitamin D performs similar tasks in the testicles.
The levels of vitamin D and the concentration of testosterone
A clinical study carried on 652 men over the age of 40 established a relation between vitamin D and testosterone. In this study, it was proven that a vitamin D deficiency of a concentration of less that 20ng / ml in the blood, is related to an insufficient concentration of testosterone. The conclusion is that a man with a low vitamin D level possibly has less testosterone than with optimal levels of vitamin D.
Low testosterone levels can lead to a low level of sexual desire, a reduction of libido, erectile dysfunction, depression, osteoporosis, and a loss and deterioration of the muscles. Moreover, as the level of testosterone drops, the risk of developing a cardiovascular disease or cancer increases, since it is a hormone that acts as a protective agent.
The effect of vitamin D in the production of testosterone
What are the effects of a vitamin D intake on the levels of testosterone? In order to test this relation, a clinical study was carried out on 165 men, between the age of 40 and 50. They were given 3.332 IU of vitamin D for a year.
The results were compared to those of a control group that was given an inefficient placebo during the same period. Both groups had insufficient levels of vitamin D and testosterone when the study began and they were healthy.
After the study, it was proven that the group that had consumed vitamin D tripled the levels of vitamin D in blood when compared to the placebo group. At the same time, those who had consumed vitamin D increased the overall testosterone levels in a 25%, and the levels of bioavailable testosterone in a 20%. On the other hand, the control group that did not consume vitamin D did not experience any increase of testosterone.
These results show that the concentration of testosterone can increase with the intake of vitamin D. It is important to highlight that the increase of bioavailable testosterone in a 20% is the way in which that hormone can be used directly by the body.
The effects of vitamin D on male fertility
Vitamin D needs the vitamin D receptors situated in the cell surface. In this way, vitamin D enters the cells and combines with determined genes in order to act on the organism.
There are vitamin D receptors in most of the tissues of the testicles. This indicates that there is a high vitamin D level in this organ. In fact, vitamin D also has other functions in this organ, apart from the regulation of testosterone.
It has been proven that vitamin D improves the quality of the male semen. The spermatozoa need to swim to the egg during the fertilization and it has been observed that they are faster after consuming vitamin D. Vitamin D produces this effect by providing the necessary “fuel” to the spermatozoa: for example, calcium, which moves faster with the help of vitamin D.
The use of vitamin D in the military field
The multiple properties of vitamin D which collaborate with the immune system, favor the cognitive function, the formation of bones, and the increase of testosterone levels, have called the attention of military people of all countries.
A vitamin D deficiency produces a deterioration of the cognitive abilities and less efficiency of the soldiers during combat. This can lead to dramatic consequences if they have to act. Low testosterone levels due to a vitamin D deficiency have a negative impact in the preparation of soldiers for combat.
It has also been found that soldiers that suffer from post-traumatic stress disorder have low testosterone levels. Vitamin D has become the “secret weapon” of the troops during combat.
Vitamin D can have can greatly help to increase the efficiency of soldiers. The most practical thing is to use vitamin D dietary supplements regularly in order to achieve an optimal hormone balance and to maintain the necessary level of vitamin D.
The side effects of vitamin D
Vitamin D is an essential and necessary vitamin for the functioning of different processes within the organism, from the formation of the bones and muscles, to the regulation of sex hormones, the brain functions and mental health. A 90% of the daily needs of vitamin D are produced in the body through the UVB sun radiation, the rest is obtained through the foods that we consume.
More than two thirds of the population have a deficient level of vitamin D due to the current lifestyle which makes it difficult to be outside and enjoy some fresh air and sunbathe. In order to make up for this deficiency we can choose to use vitamin D dietary supplements.
But, what are the correct intake levels of vitamin D and which ones can produce harmful side effects?
Recommended intake of vitamin D in order to avoid side effects
The correct amount of vitamin D depends on the body weight. For an adult with an average weight of approximately 70 kg, it is recommended to consume a daily dose of 5.000 IU, which is the adequate amount to increase and maintain an optimal level of vitamin D in 60 ng/ml.
This dose is higher than the minimal recommended intake of 800 IU daily. However, the minimal dose only avoids an acute deficiency of vitamin D and the risk of developing rickets.
A daily dose of 5.000 IU is absolutely supported by the experts, since it does not produce any side effects.
The overdose of vitamin D
An excess of vitamin D can produce an overdose. In this case, we are facing an intoxication with vitamin D. This can happen when the 25 (OH) D concentration in blood surpasses the 250 ng/ml.
However, in order to reach such a high concentration, it would be necessary to consume very high doses of vitamin D for a very long time. A vitamin D intoxication can only happen if we use 10.000 IU daily for a period of 3 months or more.
Nevertheless, the intoxication will most likely occur in the case of consuming 40.000 IU daily during at least 3 consecutive months.
Causes and symptoms of a vitamin D overdose
One of the functions of vitamin D on the skin is the regulation of calcium balance in the body, which is proven in the beneficial effect of vitamin D on bone density. The intoxication with vitamin D produces an unbalance of calcium and causes hypercalcemia. This means that the concentration of calcium in the blood serum surpasses the normal value of 2.6 mmol/1. A hypercalcemic crisis can produce a concentration of 2.5 mmol/l of calcium in the blood.
The most frequent symptoms of hypercalcemia and, therefore, of an intoxication with vitamin D, area nausea and vomits, increase in urine, excessive thirst, fever, and liquid loss. Other symptoms could include a loss of appetite, diarrhea, constipation, muscle weakness and pain, bone pain, and fatigue.
Treatment for the intoxication with vitamin D
If you experience the described symptoms and suspect that you have suffered an intoxication with vitamin D, go to the doctor immediately in order to measure the levels of vitamin D and calcium in the blood. If the levels of calcium are not high, the intoxication is not dangerous.
The treatment of an intoxication with vitamin D aims at eliminating the excess of calcium and vitamin D from the body as fast as possible. This is achieved by suspending the intake of vitamin D, following a low calcium diet, and applying an intravenous saline solution to reduce the loss of liquids. In extreme cases, it might be necessary to practice a dialysis (blood cleansing). The normalization of the levels of calcium can take several months, since vitamin D is stored in the fatty tissue of the body which is not very soluble.
Vitamin D is completely safe if it is consumed in a daily dose of up to 10.000 IU. In this case, there are no side effects. A dose of 40.000 IU or more daily can cause a vitamin D intoxication and produce hypercalcemia. In the case of suffering hypercalcemia, it is recommended to go to the doctor immediately.
- 1. Cicarma E, Porojnicu AC, Lagunova Z. Sun and sun beds: inducers of vitamin D and skin cancer. Anticancer Res. 2009; 29 (9): 3495-500.
- 2. Laura Tripkovic, Louise R Wilson, Kathryn Hart y otros. Daily supplementation with 15 μg vitamin D2 compared with vitamin D3 to increase wintertime 25-hydroxyvitamin D status in healthy South Asian and white European women: a 12-wk randomized, placebo-controlled food-fortification trial. The American Journal of Clinical Nutrition.
- 3. Jo EK. Innate immunity to mycobacteria: vitamin D and autophagy. Cell Microbiol. 2010; 12 (8): 1026-35.
- 4. Hossein-nezhad A, Spira A, Holick MF. Influence of vitamin D status and vitamin D3 supplementation on genome wide expression of white blood cells: a randomized double-blind clinical trial. Boston University Medical Center
- 5. Zittermann A, Mushroom S, Hoffmann H. Vitamin D and airway infections: a European perspective. Eur J Med Res. 2016; 21: 14.
- 6. Lemire JM, Archer DC. 1,25-dihydroxyvitamin D3 prevents the in vivo induction of murine experimental autoimmune encephalomyelitis. J Clin Invest. 1991; 87 (3): 1103-7.
- 7. Jordanes. The Origin and deeds of the goths. Mierow, CC, Ed Princeton University Press: Princeton, NJ, EE. UU., 2012; pp. 19-21.
- 8. R. Anglin, Z. Samaan, S. Walter. Vitamin D deficiency and depression in adults: systematic review and meta-analysis. Br J Psychiatry. 2013; 202: 100-7.
- 9. Eyles DW, Smith S, Kinobe R. Distribution of the vitamin D receptor and 1 alpha-hydroxylase in human brain. 2005; 29 (1): 21-30.
- 10. Vaziri F, S Nasiri, Tavana Z. A randomized controlled trial of vitamin D supplementation on perinatal depression: in Iranian pregnant mothers. BMC Pregnancy Childbirth. 2016; 16: 239a
- 11. Kaur H, Bala R, Nagpal M. Role of Vitamin D in urogenital health of geriatric participants. J Midlife Health. 2017 ene-mar; 8 (1): 28-35.
- 12. Walker RE, Bartley J, Camargo CA Jr. Higher serum 25(OH)D concentration is associated with lower risk of chronic otitis media with effusion: a case-control study. Acta Paediatr. 2017 Sep;106(9):1487-1492. doi: 10.1111/apa.13908.
- 13. Traven SA, Chiaramonti AM, Barfield WR. Fewer Complications Following Revision Hip and Knee Arthroplasty in Patients With Normal Vitamin D Levels. J Arthroplasty. 2017 Sep;32(9S):S193-S196. doi: 10.1016/j.arth.2017.02.038.
- 14. Manion M, Hullsiek KH, Wilson EMP. Vitamin D deficiency is associated with IL-6 levels and monocyte activation in HIV-infected persons. PLoS ONE. 2017; 12 (5): e0175517.
- 15. Martineau AR, Jolliffe DA, Hooper RL. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. MJ. 2017; 356: i6583.
- 16. Prof. Dr. Ingrid Gerhard. Effects of vitamin d
- 17. Grimm MO, Mett J, Hartmann T. The Impact of Vitamin E and Other Fat-Soluble Vitamins on Alzheimer´s Disease. Int J Mol Sci. 2016; 17 (11).
- 18. Bhatti AB, Usman M, Ali F. Vitamin D, cognition, and dementia: a systematic review and meta-analysis. J Clin Diagn Res. 2016; 10 (8): OE07-11.
- 19. Balion C, Griffith LE, Strifler L. Vitamin D, cognition, and dementia: a systematic review and meta-analysis. Neurology. 2012; 79 (13): 1397 – 1405.
- 20. Wang L, Hara K, Van Baaren JM. Vitamin D receptor and Alzheimer’s disease: a genetic and functional study. Neurobiol Aging. 2012; 33 (8): 1844.e1-9.
- 21. Annweiler C, FR Herrmann, Fantino B. Effectiveness of the combination of memantine plus vitamin D on cognition in patients with Alzheimer disease: a pre-post pilot study. Cogn Behav Neurol. 2012; 25 (3): 121-7.
- 22. Cannell JJ, Hollis BW, Sorenson MB. Athletic Performance and Vitamin D. Med Sci Sports Exerc. 2009 de mayo; 41 (5): 1102-10.
- 23. Visser M, Deeg DJ, Lips P. Low vitamin D and high parathyroid hormone levels as determinants of loss of muscle strength and muscle mass (sarcopenia): the Longitudinal Aging Study Amsterdam. J Clin Endocrinol Metab. 2003; 88: desde 5766 hasta 5772.
- 24. Okuno J, Tomura S, Yabushita N, y col. Low vitamin D and high parathyroid hormone levels as determinants of loss of muscle strength and muscle mass (sarcopenia): the Longitudinal Aging Study Amsterdam. Arch Gerontol Geriatr. En 2009.
- 25. Foo LH, Zhang Q, Zhu K, y col. Low Vitamin D Status Has an Adverse Influence on Bone Mass, Bone Turnover, and Muscle Strength in Chinese Adolescent Girls. J Nutr. 2009; 139: 1002-1007.
- 26. Mehran N, Schulz BM, Neri BR. Prevalence of Vitamin D Insufficiency in Professional Hockey Players. Orthop J Sports Med. 2016; 4 (12): 2325967116677512.
- 27. Koundourakis NE, Androulakis NE, Malliaraki N. Vitamin D and Exercise Performance in Professional Soccer Players. PLoS ONE. 2014; 9 (7): e101659.
- 28. Tomlinson PB, Joseph C, Angioi M. Effects of vitamin D supplementation on upper and lower body muscle strength levels in healthy individuals. A systematic review with meta-analysis. J Sci Med Sport. 2015; 18 (5): 575-80.
- 29. Boland R. Role of Vitamin D in Skeletal Muscle Function. Endocr Rev. 1986; 7: 434-448. [PubMed: 3536463]
- 30. Sorensen OH, Lund B, Saltin B, y col. Myopathy in bone loss of ageing: improvement by treatment with 1 alpha-hydroxycholecalciferol and calcium. Clin Sci (Londres). 1979; 56: 157-161.
- 31. Sato Y, Iwamoto J, Kanoko T, Satoh K. Low-Dose Vitamin D Prevents Muscular Atrophy and Reduces Falls and Hip Fractures in Women after Stroke: A Randomized Controlled Trial. Cerebrovascular Dis. 2005; 20: 187-192.
- 32. Endo I, Inoue D, Mitsui T, y col. Deletion of Vitamin D Receptor Gene in Mice Results in Abnormal Skeletal Muscle Development with Deregulated Expression of Myoregulatory Transcription Factors. Endocrinología. 2003; 144: 5.138-5.144.
- 33. Tak YJ, Lee JG, Kim YJ. Serum 25-hydroxyvitamin D levels and testosterone deficiency in middle-aged Korean men: a cross-sectional study. J Androl. 2015; 17 (2): 324-8.
- 34. Mushroom S, Frisch S, Koertke H. Effect of vitamin D supplementation on testosterone levels in men. Horm Metab Res. 2011; 43 (3): 223-5.
- 35. Angelis C, Galdiero M, Pivonello C. The role of vitamin D in male fertility: A focus on the testis. Rev Endocr Metab Disord. 2017 1 de julio.
- 36. Wentz LM, Eldred JD, Henry MD. Clinical relevance of optimizing vitamin D status in soldiers to enhance physical and cognitive performance. J Spec Opera Med. 2014; 14 (1): 58-66.
- 37. Jones G. Pharmacokinetics of vitamin D toxicity. Toxicidad. En J Clin Nutr 2008; 88 (suppl): 582S- 6S.
- 38. Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. En J Clin Nutr 1999; 69: 842-56.
- 39. Ozkan B, Hatun S, Bereket A.Vitamin D intoxication. Turk J Pediatr. 2012 Mar-Abr; 54 (2): 93-8.
- Vitamin D Dose. How much vitamin D do you need?
- Calcium, Vitamin D and Mineral Bone Density
- Supplements and Vitamins for the Health of your Skin
- Foods Rich in Vitamins and Minerals