Sun Exposure – Learn about the Health Benefits

Sun Exposure – Learn about the Health Benefits

What are the benefits of Sun Exposure? How much time is recommended to sunbathe? We analyse what science says about it

Sun, Enemy or Ally?

Health authorities around the world warn about the dangers of the sun and recommend avoiding or reducing exposure to the energy emanating from our star king

The justification behind such recommendations usually falls on photoaging and the increased risk of skin cancer.

But things are not that easy. In Medicine and Health they almost never are.

On the other hand, we have a growing scientific literature that shows us the multiple benefits that moderate sun exposure has.


Yes, you are all thinking about , but this goes far beyond that vitamin

We will talk about the risks and benefits of sun exposure and what I think should be the message and the Public Health recommendations that the population has to understand

A historical-evolutionary perspective

The first medical use of the sun as a therapy was born in 1919 when the scientific community realized that so-called “sun cures” could cure rickets, a devastating disease that occurs in children (1).

This empirical finding was followed by the discovery in 1924 of a lipid precursor that, present in the skin and diet, could be converted by ultraviolet radiation into an “antirachitic” substance (2).

That is, it was vitamin D and it was not until 1931 that it was defined as such.

Later, in the 1960s, a correlation was found between sun exposure and different types of cancer, especially prostate, colorectal and breast cancer, and a hypothesis was launched:

Could the sun or vitamin D be the protective factor in this risk variation?

Sun and facial skin

Much has been said since then, and if you are interested in the subject and want to delve into it, in this article published several years ago you can expand (3)</em >

Later, the debate in the scientific community focused on the risks of sun exposure and the use of sunscreens, and until very recently this has been the predominant discourse in Medicine.

“The sun is bad. Protect yourself.” No nuances. But there are. And many…

How could it be otherwise? The human being has literally evolved under the sun

The fact that our skin organ has defence mechanisms against ultraviolet radiation only confirms that we have evolved together with the sun and that our different phototypes respond to the different protection needs with respect to our native geography.

And if there are skin mechanisms that protect us from the sun, does this not mean that it is bad per se?

No, I was already telling you that things are not that simple. But first, let’s talk about the true risks of inadequate sun exposure

Sun exposure and melanoma

The three words above are key: “Inadequate sun exposure”

And it is one of the things that should be clear to you after reading this post: there are adequate forms and inappropriate forms of sun exposure.

Beneficial ways and harmful ways.

As we said at the beginning, the main justification for the message against the sun is that the scientific community has realized that sunburn is associated with a doubled risk of melanoma compared to people who do not burn (4)

Melanoma is a tumour that no one would want to have…

It is a neoplasm that can go unnoticed for a long time. A neoplasm that metastasizes with surprising ease. In short, a very treacherous disease.

I have seen boys and girls under the age of 30 see their lives cut short by melanoma.

So melanoma is scary…

But creating in the population the feeling that sunbathing will greatly increase our chances of having melanoma is not only reductionist, it is also dangerous.

Sun exposure and vitamin D

We know that the general population not trained in health likes messages that are clear and simple to understand, with as few nuances as possible

“The sun will give you cancer” is a simple message to understand and that is why the “anti-sun” campaign has sold so well

Why has melanoma increased

Of course, the keeps growing too

Up to a third of individuals in most developed countries have vitamin D deficiency, which far from being a vitamin, acts at multiple levels maintaining our homeostasis as individuals.

So, the hypothesis that I would start to manage as to why there has been an increase in the incidence and prevalence of malignant melanoma would be:

  • Sun exposure that causes burn (sunburn sun exposure) continues to rise
  • Moderate sun exposure that DOES NOT cause burns has been decreasing. Intervention that we remember, is protective.
The result? Organisms less photo-adapted, more vulnerable to DNA damage caused by the sun and deficient in vitamin D

Moderate sun exposure

What is often forgotten is that, while sun exposure that causes sunburn greatly increases the risk of melanoma, moderate sun exposure (non-burning sun exposure) it seems to reduce the risk.

Outdoor workers have a lower incidence of melanoma than indoor workers, as several meta-analyses have shown (5).

By what biological mechanisms does intense sun exposure increase the risk of melanoma?

Well, basically, UVB radiation causes DNA damage by creating pyrimidine dimers and free radicals.

So why are outdoor workers at lower risk than indoor workers?

Because moderate and progressive sun exposure is probably a hermetic stimulus that enhances the intrinsic defence mechanisms that all our cells have, including the melanocytes of the skin

We talk about:

  • DNA repair enzymes,
  • Inhibition of the cell cycle and cell growth,
  • Less proliferation,
  • Increased apoptosis,
  • Greater cell differentiation or anti-inflammatory mechanisms.

Bad habits when sunbathing

The paradox is that many of these mechanisms at the cellular level areinduced by the same vitamin D that we generate due to sun exposure (6)

The prevalence and incidence of melanoma has grown dramatically.

From 1 case per 100,000 inhabitants in the year 1935 to 23 cases per 100,000 inhabitants in the year 2012. The hypotheses raised in view of this fact point to the increase in diagnostic methods and the depletion of the Ozone layer.

But neither is very convincing…

Bad sunbathing habits

What we need to start thinking about is that our behaviour has changed considerably

  • A few years ago 25% of Americans lived in the countryside.
  • Only 2% do so today.

In Spain the situation is not very different.

Uncontrolled sun exposure continues to rise. The tourism of “costa del sol”, as I call it, continues to grow.

These are individuals who spend 340 days a year inside an office and 20 days a year exposing themselves to the sun for 10 hours a day

Population with vitamin D deficiency

Vitamin D is a hormone with very broad and varied functions in multiple organs and systems

It has receptors in most body tissues, a fact that emphasizes its importance and at the same time explains why epidemiological studies have linked vitamin D deficiency to so many diseases.

Today most scientific societies consider vitamin D insufficiency at values 20-30 ng/mL and vitamin D deficiency values <20 ng/mL.

If we focus on the range of insufficiency, more than two thirds of the population would be considered insufficient in vitamin D

This has two readings: either we are making a mistake with the ranges, or something big is happening with this hormone-vitamin.

How much of the Sun is good for health?

Next, we will comment on the main conditions that have been related to sun exposure.

It is worth saying that when we talk about the benefits of the sun, we cannot rule out the influence of multiple confounding factors related to sun exposure.

Mortality from any cause

Chowdhury conducted a 2014 meta-analysis of 73 cohort studies and 22 clinical trials that found an inverse association between circulating vitamin D levels and the risk of death from cardiovascular, cancer, and other causes ( one).

Schottker found the same in 2014 (2). Lindqvist in 2014 studied a cohort of Swedish women who had suffered from melanoma (Melanoma Southern Swden cohort) and concluded that those who avoided sun exposure at all costs died more.

In Lindqvist’s words :

“Our finding that avoidance of sun exposure was a risk factor for all-cause death of the same magnitude as smoking is novel”

That is, what they found in this study was that avoiding the sun conferred an increased risk of mortality of the same magnitude as smoking (3)

The same guides have to rectify some things…

Colorectal cancer

Rebel et al found in animal models how moderate exposure to UV radiation reduced the incidence of malignant colon tumors (4).

In addition, they compared the effect of vitamin D supplementation, a diet rich in vitamin D and sun exposure.

Only the latter managed to reduce the incidence of malignant tumors

The latest report from the US Institute of Medicine found that those patients with vitamin D levels >40 ng/mL had a 42% lower risk of colorectal cancer compared to patients who had levels < 10ng/mL (5).

Breast cancer

Mohr conducted a meta-analysis in 2015 on patients who had had breast cancer.

It found that those with vitamin D levels of >32 ng/mL had approximately half the risk of death from cancer progression compared to those with 14 ng/mL levels (6).

Bladder cancer

Zhao et al found in 2016 a 30% reduction in the risk of bladder cancer when vitamin D concentrations rose above 30 ng/mL compared to <15 ng/mL (7).

Cardiovascular disease

A paradox that we find when studying these issues is that cardiovascular mortality is not always diminished in those individuals who have low levels of vitamin D

Liu et al. were able to find the key by discovering that sun exposure releases cutaneous deposits of nitrogen oxides into the blood that produce systemic vasodilation secondary to UVA radiation, lowering blood pressure figures (8).

That is, as we said, the sun is much more than vitamin D…

Metabolic syndrome and type 2 diabetes

Vitezova (2015) found another interesting association between vitamin D levels and in a cohort of 3240 older adults.

Interestingly, the association was still present after adjusting for BMI (9).

Clemente-Postigo et al., in 2015, found another similar finding: low levels of vitamin D were associated with type 2 diabetes independently of BMI (10).

But even more interesting, Geldenhuys found that it was not vitamin D levels that were associated with a decreased risk of T2DM and obesity, but levels of exposure to ultraviolet radiation</strong >, so vitamin D seemed to be more of a marker than a cause of the decreased risk (11)

That said, the sun is much more than vitamin D…

Conclusions and Take aways

We could continue with Alzheimer’s disease, cognitive impairment, type 1 diabetes, psoriasis, liver disease, statin intolerance, myopia or obesity, but I have to go make those infographics that you like so much (if you want we can do a third part).

In short, the message that would take me home after reading the article would be the following:

  • The intense sun exposure that causes burns is negative and has been related to an increased risk of serious diseases. Therefore, we should avoid it at all costs.
  • On the other hand, moderate and progressive sun exposure is not only not negative (to date it has not been convincingly related to serious pathologies), but it also confers protection against multiple diseases in ways we are still beginning to understand.

solar exposition

The sun is much more than just vitamin D and we humans probably need some exposure to it for optimal health

I always put you on the same assumption, if you want to emulate optimal health conditions, introduce those elements that have been with us most of the time (physical activity, real food, sun< /strong>) and eliminate those that carry with us very little (chronodisruption, endocrine disruptors, ultra-processed products, sedentary lifestyle)

Bibliographical Sources

  1. The Cure of Infantile Rickets by Sunlight. Am J Med Sci. 1922;
  3. Bandera Merchan B, Morcillo S, Martin-Nuñez G, Tinahones FJ, Macías-González M. The role of vitamin D and VDR in carcinogenesis: Through epidemiology and basic sciences. J Steroid Biochem Mol Biol [Internet]. 2016;167:203–18.
  4. Gandini S, Sera F, Cattaruzza MS, Pasquini P, Picconi O, Boyle P, et al. Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure. Eur J Cancer [Internet]. 2005 Jan [cited 2015 Nov 4];41(1):45–60.
  5. Mark Elwood J, Jopson J. Melanoma and sun exposure: An overview of published studies. Int J Cancer. 1997;
  6. Sequeira VB, Rybchyn MS, Tongkao-On W, Gordon-Thomson C, Malloy PJ, Nemere I, et al. The role of the vitamin D receptor and ERp57 in photoprotection by 1α,25-dihydroxyvitamin D3. Mol Endocrinol. 2012;26(4):574–82.
  7. Chowdhury R, Kunutsor S, Vitezova A, Oliver-Williams C, Chowdhury S, Kiefte-De-Jong JC, et al. Vitamin D and risk of cause specific death: Systematic review and meta-analysis of observational cohort and randomised intervention studies. BMJ. 2014;
  8. Schottker B, Jorde R, Peasey A, Thorand B, Jansen EHJM, Groot LD, et al. Vitamin D and mortality: meta-analysis of individual participant data from a large consortium of cohort studies from Europe and the United States. Bmj [Internet]. 2014;348(jun17 16):g3656–g3656.
  9. Lindqvist PG, Epstein E, Landin-Olsson M, Ingvar C, Nielsen K, Stenbeck M, et al. Avoidance of sun exposure is a risk factor for all-cause mortality: Results from the Melanoma in Southern Sweden cohort. J Intern Med. 2014;
  10. Rebel H, Dingemanse-Van Der Spek C, Salvatori D, Van Leeuwen JPTM, Robanus-Maandag EC, De Gruijl FR. UV exposure inhibits intestinal tumor growth and progression to malignancy in intestine-specific Apc mutant mice kept on low Vitamin D diet. Int J Cancer. 2015;
  11. Jenab M, Bueno-de-Mesquita HB, Ferrari P, van Duijnhoven FJB, Norat T, Pischon T, et al. Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations:a nested case-control study. BMJ. 2010;
  12. Mohr SB, Gorham ED, Kim J, Hofflich H, Garland CF. Meta-analysis of vitamin D sufficiency for improving survival of patients with breast cancer. Anticancer Res. 2014;
  13. Zhao Y, Chen C, Pan W, Gao M, He W, Mao R, et al. Comparative efficacy of vitamin D status in reducing the risk of bladder cancer: A systematic review and network meta-analysis. Nutrition. 2016.
  14. Liu D, Fernandez BO, Hamilton A, Lang NN, Gallagher JMC, Newby DE, et al. UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase. J Invest Dermatol. 2014;
  15. Vitezova A, Zillikens MC, Van Herpt TTW, Sijbrands EJG, Hofman A, Uitterlinden AG, et al. Vitamin D status and metabolic syndrome in the elderly: The Rotterdam Study. Eur J Endocrinol. 2015;
  16. Clemente-Postigo M, Muñoz-Garach A, Serrano M, Garrido-Sánchez L, Rosa Bernal-López M, Fernández-García D, et al. Serum 25-Hydroxyvitamin D and Adipose Tissue Vitamin D Receptor Gene Expression: Relationship With Obesity and Type 2 Diabetes. Obes Nutr. 2802;
  17. Geldenhuys S, Hart PH, Endersby R, Jacoby P, Feelisch M, Weller RB, et al. Ultraviolet radiation suppresses obesity and symptoms of metabolic syndrome independently of vitamin D in mice fed a high-fat diet. Diabetes. 2014;

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About Borja Bandera
Borja Bandera
Borja Bandera, a young doctor dedicated to the areas of nutrition, exercise and metabolism, combines his clinical activity with his vocation for dissemination.
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