Too much sun can be toxic … but it seems that the opposite is also dangerous.
There's no doubt that excess sunlight can cause skin cancer, depending on a range of factors.
These include the amount of UV radiation you get, your skin shade, and your personal genetic profile.
But growing evidence suggests that dermatologists' well-meant advice to minimize sun exposure may be worse than misguided.
At minimum, excessive sun-avoidance may promote hypertension, auto-immune disorders, cardiovascular disease, major cancers, and ailments associated with vitamin D deficiency.
Now, a study among Swedish women provides evidence suggesting that excessive sun-avoidance may cut your life short.
Can sun avoidance lead to premature death?
No epidemiological study can prove a cause-and-effect relationship between a lifestyle factor and the risk of a disease.
That said, the results of a very large epidemiological study fit with what's known about the effects of sunshine-generated vitamin D and overall health.
Researchers from Sweden's famed Karolinska University compared the sun exposure habits of 29,518 Swedish women to their risk for skin cancer (Lindqvist PG et al. 2014).
Their analysis showed that the women who strictly avoided the sun over the study's 20 years period were twice as likely to die prematurely, compared with women who got average sun exposure.
Critically, the women who reported normal sun exposure were not significantly more likely to have developed malignant melanoma or died from melanomas.
This fits with the results of a previous Swedish study that followed 38,472 women for 15 years and found that sun exposure was associated with reduced risk of both cardiovascular and overall death (Yang L et al. 2010).
As we said, epidemiological studies cannot prove a cause-effect relationship ... but attention should paid to large ones like these.
Why would sunlight extend life?
The women who got more sun may have had healthier diets and lifestyles overall.
But it could well be that excessive sun-avoidance raises the risk of death, for several reasons.
Sunlight may enhance endocrine (hormonal) function, maintain healthy mood, and boost DNA repair capacity, all of which could help extend lifespan (Berwick M 2011).
Sunlight stimulates vitamin D production in the body, and vitamin D deficiency is a risk factor in major cancer types as well as for heart disease, stroke, hypertension, autoimmune diseases (e.g., MS), type 1 and 2 diabetes, depression, birth defects, infectious diseases, and more.
Sunlight stimulates the production of nitric oxide, which relaxes blood vessels, thereby reducing blood pressure.
In line with this fact, clinical studies dating back to the 1970's showed that blood pressure was consistently lower in summer than winter.
Epidemiological studies link living at sun-poor latitudes to hypertension and higher average blood pressure, comparedwith living closer to the equator.
And a recent clinical experiment found that UV light lowered blood pressure.
As its lead author Richard Weller, M.D., said, “We suspect that the benefits to heart health of sunlight will outweigh the risk of skin cancer. The work we have done provides a mechanism that might account for this, and also explains why dietary vitamin D supplements alone will not be able to compensate for lack of sunlight.” (UE 2011)
Epidemiological studies link living in sunny climes to a lower risk for autoimmune diseases like multiple sclerosis and type 1 diabetes.
How much sun should I get?
We recommend that you follow the guidelines offered by the vitamin D Council.
The most natural way to get vitamin D is by exposing your bare skin to sunlight (ultraviolet B rays). This can happen very quickly, particularly in the summer. You don't need to tan or burn your skin to get vitamin D. You only need to expose your skin for around half the time it takes for your skin to turn pink and begin to burn. How much vitamin D is produced from sunlight depends on the time of day, where you live in the world and the color of your skin. The more skin you expose the more vitamin D is produced.
Does sunlight cause deadly melanoma-type skin cancers?
Melanoma is the most dangerous and potentially lethal of the three types of skin cancer, because it typically metastasizes (spreads) into other body parts.
The other two types – squamous cell carcinoma and basal cell carcinoma – are much more treatable and not as threatening or able to metastasize as melanoma.
Advocates of sun-avoidance point out that the incidence of melanoma increases as distance to the equator decreases.
But the late, widely esteemed dermatologist A. Bernard Ackerman, M.D., told The New York Times that the link between melanoma and sun exposure was “not proven” and “the field is just replete with nonsense.” (Kolata G 2004)
Dr. Ackerman deemed the epidemiological evidence linking long residence in sunny latitudes to melanoma to be of dubious value, and noted that epidemiological studies have led researchers astray when searching for the causes of other cancers.
He also questioned whether the supposed “epidemic” of melanoma exists, because doctors now define as melanomas many skin growths that would not previously have met the criteria.
As he noted, blacks and Asians get malignant melanoma almost exclusively on skin not exposed to sunlight: the palms, soles, nails and mucous membranes.
And even in whites, the most common melanoma sites – legs in women, trunks in men – are not the most sun-exposed body parts.
Dr. Ackerman advised moderation in sun exposure … but primarily to avoid premature skin aging and to prevent squamous cell carcinoma, a much less dangerous cancer than malignant melanoma.
Overall, it seems wise to avoid burning, but unwise to go to extremes of sun avoidance.
And it's not clear that dietary vitamin D – best obtained from fatty seafood or from supplements – can fully substitute for the benefits of sunlight.
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- Fears TR, Bird CC, Guerry D 4th, Sagebiel RW, Gail MH, Elder DE, Halpern A, Holly EA, Hartge P, Tucker MA. Average midrange ultraviolet radiation flux and time outdoors predict melanoma risk. Cancer Res. 2002 Jul 15;62(14):3992-6.
- Feelisch M, Kolb-Bachofen V, Liu D, Lundberg JO, Revelo LP, Suschek CV, Weller RB. Is sunlight good for our heart? Eur Heart J. 2010 May;31(9):1041-5. doi: 10.1093/eurheartj/ehq069. Epub 2010 Mar 9.
- Kolata G. I Beg to Differ; A Dermatologist Who's Not Afraid to Sit on the Beach. The New York Times. July 20. 2004. Accessed at http://www.nytimes.com/2004/07/20/health/i-beg-to-differ-a-dermatologist-who-s-not-afraid-to-sit-on-the-beach.html
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- The University of Edinburgh (UE). Sunshine could benefit health. Accessed at http://www.ed.ac.uk/news/2013/sunshine-080513
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