L-Carnitine is one of the most popular supplements used during cutting phase or fat loss processes. In this article, we are going to explain the main properties of carnitine to improve the physical composition.
L-carnitine or carnitine is made up of amino acids and it is a component of most of the cells of our body. Its name comes from the Latin word “carnus” (which means “meat”) because it was first isolated from meat.
Carnitine is the generic term for several compounds, such as L-carnitine L-tartrate, acetyl-L-carnitine and propionyl L-carnitine. 
- 1. What is L-carnitine?
- 2. Types of L-carnitine
- 3. Effects of L-carnitine
- 4. Dose of L-carnitine
- 5. Sources of L-carnitine through food
- 6. L-carnitine supplements
- 7. Carnitine metabolization
- 8. L-carnitine deficiency
- 9. L-carnitine and the brain function
- 10. Benefits of L-carnitine on male fertility
- 11. L-carnitine and sport performance
- 12. L-carnitine and the heart
- 13. Proper functioning of the immune system
- 14. L-carnitine and the peripheral arterial disease
- 15. L-carnitine and the aging process
- 16. L-carnitine and type II diabetes
- 17. L-carnitine, HIV and AIDS
- 18. L-carnitine and renal insufficiency
- 19. L-carnitine and other diseases
- 20. Who needs to take L-carnitine?
- 21. Side effects of L-carnitine
- 22. L-carnitine and interactions with other medicines
- 23. Combination with other supplements
- 24. L-carnitine dietary supplements
- 25. Bibliography:
- 26. Related Entries:
What is L-carnitine?
Carnitine plays an essential role in order to provide energy for the body. It is in charge of transporting the long chain fatty acids to the mitochondria. There, they are burnt to produce energy. Moreover, carnitine also takes toxic substances out of the cells. Carnitine can be found in tissues from the skeletal muscle or the heart, which use fatty acids as fuel.
L-carnitine is an amine synthesized from two essential amino acids, lysine and methionine.
Most people produce enough carnitine to meet the demands of their body. However, sometimes the body is not capable of producing enough carnitine which can be due to a disease or genetics (like in the case of premature babies).
To sum up, L-carnitine burns fat and improves the physical performance. This is due to the fact that it increases the energy, improves the oxygen absorption and the protein metabolism.
Then, it is vital for physical exercise because it improves the performance, decreases the fatigue and shortens the post-workout recovery.
Types of L-carnitine
L-carnitine is the traditional form of biologically active carnitine. It can be found in our own body, food and most supplements.
There are other types of carnitine, which we are going to comment now:
This is one of the most used forms in sport supplementation due to its high absorbability. It helps to relieve the muscle soreness caused by physical exercise while improving the recovery.   
Also known as ALCAR, this form is the most effective compound for the brain. This is due to the fact that it can cross the blood-brain barrier, improving the functioning of the brain and neurological disorders, such as dementia or Alzheimer.
This is the best form to treat circulatory disorders, such as the peripheral vascular disease or hypertension. Its efficacy is mainly due to the nitric oxide production, which improves the blood flow.  
An inactive form that can trigger a carnitine deficiency, since it inhibits the absorption of other useful carnitine compounds. 
For most people, acetyl-L-carnitine and L-carnitine tartrate are the most effective forms. However, you have to choose the form that better suits your needs and personal objectives.
Effects of L-carnitine
L-carnitine provides benefits for our health by supporting the functioning of the mitochondria. The mitochondria play a vital role in preventing diseases, delaying aging processes and supporting our vitality and health.   
One of the most important benefits of L-carnitine consists of producing energy for the cells.    L-carnitine improves the fatty acid transport to the mitochondria. The mitochondria are like engines that transform the fatty acids into energy so that the body can perform several tasks.  
Around a 98% of the L-carnitine reserves of the body are stored in the muscles, heart and brain. There are also small amounts in the liver and blood. 
Apart from being synthesized by our own body, we can obtain L-carnitine from animal products like meat or fish. 
Vegans or those who suffer certain genetic problems run the risk of not producing enough carnitine. This is why it has to be obtained from external sources. 
To sum up, L-carnitine provides energy and strength, improving the physical performance in those who do physical exercise and helping to lose weight. Moreover, it improves the functioning of the fat metabolism, stimulating the mind and protecting the nervous system.
Dose of L-carnitine
The recommended daily dose of L-carnitine is between 500mg and 3,000mg (1,000 milligrams = 1 gram). Even though the dose changes from one study to another, we are going to come up with a general description for the recommended dose for each type of carnitine:
This type of carnitine is the best for the intellectual performance and to improve our health. The dose is between 500mg and 2,000mg daily. You should start taking 500mg daily in the morning and increase it progressively according to your needs. Acetyl-L-carnitine tends to have a slightly stimulant effect, which is why you should not take it in the evening nor at night.
This type of carnitine improves the blood flow in those who suffer hypertension or any problem related to the blood pressure. The dose changes between 400mg and 1,000mg daily.
After reviewing the data about L-carnitine, the scientists have concluded that a dose up to 2,000mg is advised taken for a long time. In addition, it is the most effective dose than most L-carnitine types.
L-carnitine has been deeply studied due to its importance when it comes to producing energy. In general, it is a dietary supplement that is well tolerated and safe. 
Sources of L-carnitine through food
Animal produces like meat, fish, poultry and milk contain more carnitine. Beef has the highest carnitine content from them all. 
Dairy products also have carnitine, specially whey.
Carnitine can be found in two forms, known as D and L which are specular images (isomers). 
Carnitine content per gram of product:
- Beef: 170g – 160mg
- Pork: 170g – 50mg
- Chicken: 170g – 6mg
- Whole milk: 235ml – 8mg
- Cooked cod: 115g – 4 to 7mg
- Cooked chicken breast: 115g – 3 to 5mg
- Ice cream: 120ml – 3mg
- Cheddar cheese: 57g – 2mg
- Whole bread: 2 slices – 0.2 mg
- Cooked asparagus: around 120g – 0.1mg
We should take into account that only between 54 and 87% of the carnitine content from food can be used by the body.
It is very difficult to get the proper amount of L-carnitine that the body needs just through natural sources.
To avoid a L-carnitine deficiency, the best solution consists of taking a L-carnitine dietary supplement every day.
L-carnitine dietary supplements are available in liquid, capsule and powder format. The liquid and powder can be easily dissolved in water or juice, while the capsules are easier to transport.
Adults who follow an omnivore diet that includes red meat and other animal products, take around 60-180 milligrams of carnitine daily. 
Vegans obtain less carnitine from the diet (around 10-12 milligrams) because they do not eat animal products. Most of the carnitine (54-86%) from food is absorbed by the small intestine and goes directly to the bloodstream.
The kidneys store carnitine, which is why low carnitine diets have little impact on the overall carnitine levels in the body.  A carnitine excess is excreted through the urine whenever it is necessary in order to keep the blood levels stable.
There are two different types of carnitine deficiency. A primary deficiency, which is a hereditary disorder of the cell carnitine transport system. It generally happens around the age of five with cardiomyopathy symptoms, skeletal muscle weakness and very low blood sugar levels.
A secondary carnitine deficiency can be due to certain diseases (like chronic renal insufficiency) or certain factors (like taking certain antibiotics). This hinders our ability to absorb carnitine or it can abnormally increase its excretion. In this cases, it is very important to take carnitine supplements, after consulting your doctor.
L-carnitine and the brain function
Clinical studies have proven that taking acetyl-L-carnitine daily counters the brain deterioration associated with Alzheimer and other brain diseases. Moreover, it also has positive effects on the brain function in those who do not suffer Alzheimer nor other brain diseases.   
It is necessary to carry out a wider research to see the long-term effects of L-carnitine on healthy people.
Benefits of L-carnitine on male fertility
The carnitine content in seminal fluid is directly connected to the sperm quantity and motility  . This means that L-carnitine can be beneficial to treat male infertility. Several clinical studies have proven that carnitine supplementation (from 2,000 to 3,000mg daily for a period of 3-4 months) can improve the sperm quality.   
A double blind, cross-over, blind study treated 100 infertile men with a daily dose of 2,000mg of carnitine for 2 months. The results showed how their sperm improved both in terms of its quantity and in its general or progressive motility. 
These positive results could be due to the increase in mitochondrial oxidation of fatty acids (due to the energy supply). Or it could also be due to the decrease of cell death in the testicles. 
However, to evaluate the potential benefits of carnitine to treat male infertility, we need longer and more precise studies.
L-carnitine and sport performance
When it comes to the effect of L-carnitine on the sport performance, the experts do not completely agree. However, several clinical studies have proven a slight improvement using high doses of L-carnitine for a long period of time.  
Some athletes take carnitine to improve their physical performance. However, after twenty years of research, we cannot completely ensure that carnitine supplements improve the performance of healthy people. The clinical studies used daily doses between 2,000 and 6,000mg during one and 28 days.   
The total carnitine content of the body is approximately 20 grams in men who weigh 70gk. Most of it is present in the skeletal muscle. Therefore, carnitine supplements do not increase the use of oxygen during the exercise, nor the carnitine levels in the muscles.
L-carnitine and the heart
A short term clinical study administered carnitine orally and it was injected with anti-ischemic effect. This placebo-controlled, double blind study was conducted in Italy on 2,330 patients who have suffered an acute myocardial infarction. They were given either a carnitine supplement (5 days 9g/day intravenously for 6 months 4g/day orally) or a placebo.  The result was that the L-carnitine treatment significantly reduced the mortality rate 5 days after the randomization. However, it did not affect the risk of suffering heart insufficiency or death after 6 months.
The authors of a meta-analysis performed in 2013 combined the results of this study with other 12 studies.  They concluded that the L-carnitine treatment in acute myocardial infarction patients for 2 months reduces the mortality rate in a 27%. It also reduces the ventricular arrhythmia in a 65% and angina pectoris in a 40%. However, it does not reduce the risk of suffering a heart insufficiency or another heart attack.
In another study, the participants were given 2,000mg of acetyl-L-carnitine daily. This lowered the systolic blood pressure, which is an important marker for cardiovascular health. In addition, it also reduced the chances of suffering this disease in almost 10 points.
Chronic heart insufficiency
The study also proved how L-carnitine improves the situation of patients who suffer a serious heart disease. This is the case of the coronary heart disease or a chronic heart insufficiency. 
There was another clinical study that lasted 12 months. In it, the participants who took L-carnitine supplements reduced the heart insufficiency percentage and the deaths connected to this pathology. 
Another clinical study was carried out in 2013 with 2,595 people. In it, it was discovered that L-carnitine transformed into Trimethylamine n-oxide (TMAO) by the intestinal microbiota. TMAO is a substance related to the risk of suffering cardiovascular diseases. 
The participants who ate meat produced more TMAO than vegans or vegetarians after taking L-carnitine. This was mainly due to the differences in terms of their intestinal bacteria. Moreover, the study also found a connection between high plasma L-carnitine levels on an empty stomach and the risk of suffering: coronary diseases, peripheral arterial disease and general cardiovascular disease in the case of participants who had high TMAO concentrations.
The studies can explain the relation between a high red meat intake (a carnitine rich source) with a higher risk of suffering a cardiovascular disease. However, we still need more research to understand the effects of carnitine on the cardiovascular system in depth.
Proper functioning of the immune system
Moreover, L-carnitine works as an antioxidant, preventing the free radicals from destroying the cells and tissues.
It specially protects the membranes and nervous cells, avoiding the breakdown of neurons. Therefore, it can prevent the onset of degenerative neurological diseases such as Alzheimer or Parkinson.
L-carnitine and the peripheral arterial disease
Several studies have proven the efficacy of carnitine dietary supplement to treat heart ischemia (restriction of the blood flow to the heart). It can also treat peripheral arterial disease (whose main symptoms is a bad blood circulation in the legs, known as intermittent claudication). 
The intermittent claudication is due to a bad blood supply in the legs that leads to an acetyl-carnitine accumulation in the muscle. The patients who suffer peripheral arterial disease that develop claudication have a hard time doing exercise and walking even short distances. The research has shown that carnitine improves the skeletal muscle performance in the leg.
A clinical study gave L-carnitine supplements (as propionyl L-carnitine 2g/day for 12 months) to patients who suffer from moderate to severe intermittent claudication. Their quality of life significantly improved when compared to those patients who were given placebo only. 
In a similar study, carried out in the United States, the same daily carnitine dose was given to patients with claudication for 6 months. It managed to relieve the physical pain and improve the participants’ health in general when compared to the control group. 
The authors of the 12 random clinical essays review concluded that propionyl L-carnitine significantly increased the distance that the patients could run. 
These results show how taking L-carnitine for a year has a positive effect on the cardiovascular system of certain patients. Although other studies discuss some problems of a prolonged carnitine intake for the heart and circulation.
L-carnitine and the aging process
A lower mitochondrial function accelerates the aging process. The carnitine content in the tissues drops with age, which affects the mitochondrial membrane integrity.  Previous studies on mice have proven that high doses of acetyl-L-carnitine and alpha lipoic acid (an antioxidant) reduces the mitochondrial breakdown  . The mice who were given these supplements moved more and had a better performance in memory-related tasks.
However, there are no similar studies in humans. A meta-analysis suggests that acetyl-L-carnitine improves the memory and reduces the mental deterioration in adults with mild cognitive deterioration and Alzheimer.  In these studies, the subjects were given 1,500 to 3,000mg of acetyl-L-carnitine daily between 3 and 12 months.
L-carnitine and type II diabetes
The insulin resistance plays an important role in the onset of type II diabetes. It is related to an altered fatty acid oxidation in the muscles. We are not sure if the mitochondrial dysfunction is what causes the development of this disease. The fat accumulation in the tissue has become an insulin resistance marker. 
There was a recent analysis of two multi-centered clinical trials on subjects with type I or type II diabetes. The results were that an oral acetyl L-carnitine treatment (3,000mg/day) for a year significantly relieves neuropathic pain, as well as improving the state of patients with diabetic neuropathy. The treatment was more effective in patients with type II diabetes.
A clinical trial conducted on patients with type II diabetes showed how L-carnitine improves the blood sugar response with carbohydrate-rich meals. this reaction is an important marker for the risk of diabetes and our health in general. 
Moreover, L-carnitine also fights against diabetes by increasing a key enzyme called AMPK. This element improves our ability to use carbohydrates. 
L-carnitine, HIV and AIDS
The human immunodeficiency virus (HIV) reduces the lymphocytes number (a type of white cells). Consequently, this results in the acquired immunodeficiency syndrome (AIDS). People who have the HIV accumulate fat in certain parts of the body, while it breaks down in others. It also increases the blood fat (hyperlipidemia) and the insulin resistance, which triggers what is known as lipodystrophy syndrome.
This syndrome is a symptom of mitochondrial toxicity caused by a HIV infection. The anti-viral medicines produce a carnitine deficiency which affects the mitochondrial fat metabolism. 
The molecular mechanisms that trigger this pathology are still unknown. The research provides contradictory results . However, they suggest that both oral and intravenous carnitine supplementation can slowly kill the lymphocytes in patients with HIV (with daily doses of 2,000 to 6,000mg for several weeks or months). It can even stop the development of the HIV  and improve the blood lipid levels.   
L-carnitine and renal insufficiency
Those who suffer renal insufficiency experience an imbalance in several aspects: lower synthesis, increased excretion produced by the kidneys, loss of appetite which reduces the amount of food that we eat, specially less animal products.
Many patients with CKD (chronic kidney disease), specially those who are subjected to hemodialysis of carnitine. A low carnitine level, both in the blood and in the muscles, causes anemia, muscle weakness, fatigue, alteration of the blood lipid levels and the onset of heart diseases. Several studies have proven how high doses of carnitine supplements in the long term (sometimes injected) can improve the hemodialysis treatment. However, these studies have been done on a small number of patients and there are no double blind studies.
L-carnitine and other diseases
After a chemotherapy or radiotherapy treatment, cancer patients tend to experience fatigue, follow a bad diet and have a carnitine deficiency . A clinical trial tested how a carnitine treatment (4,00mg/day for a week) in patients undergoing chemotherapy decreased the fatigue. Moreover, it also balanced the blood carnitine levels. 
Another study carried on patients with terminal cancer treated with carnitine (doses between 250mg to 3,000mg/day) observed how it improved the mood and quality of sleep, as well as decreasing the fatigue. In both studies, most of the subjects have a carnitine deficiency before starting to take carnitine supplementation.
Who needs to take L-carnitine?
The carnitine levels of each person will depend on the diet and the amount of carnitine synthesized by the body. Carnitine levels are usually lower among vegetarians and vegans, since they avoid eating animal products. 
Due to this, it is advisable for vegetarians and vegans to take L-carnitine supplements. However, there are not clinical trials conducted on vegans and vegetarians to this date.
A clinical trial proved how taking 2,000mg of L-carnitine can decrease the fatigue and enhance the muscle function in the elderly. Another research has proven that acetyl-L-carnitine also improves the cognitive performance and health of old people. 
Those who suffer from cirrhosis or kidney disease also run the risk of suffering a carnitine deficiency. That is why carnitine supplements can be useful in these cases. 
Side effects of L-carnitine
There was a clinical trial to assess the safety of L-carnitine. The participants were given 3,000mg of carnitine daily for 21 days. At the beginning and the end of the study, the participants had a complete blood test and there was no negative effects reported. 
According to a report about the safety of L-carnitine, a daily dose of around 2,000mg is safe in the long term. Some people may experience side effects like nausea or indigestion, but there were no serious issues in any case. 
Those who suffer or who have a history of epilepsy attacks should not take L-carnitine.
L-carnitine and interactions with other medicines
Carnitine interacts with antibiotics containing pivalate, such as pivampicillin, which is used to prevent urinary tract infections. The long term treatment with these antibiotics can trigger a carnitine deficiency. Even though the carnitine levels drop when the fatty acid oxidation is inhibited, it has not been proven that this effect leads to a carnitine deficiency.
Combination with other supplements
Carnitine can be taken with other supplements, creating a synergy.
L-carnitine dietary supplements
L-carnitine tartrate, acetyl-L-carnitine and propionyl-L-carnitine are available as food supplements. Carnitine contributes to weight loss processes, provides energy during physical exercise and improves the well being in general.  The Food and Drugs Administration (FDA) from the United States has accepted its use to treat a primary and secondary carnitine deficiency.
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