June 27, 2015
The evidence that sunlight is good for our health continues to grow while our assumption that the benefits are due solely to vitamin D continues to fade. New information on sunlight producing nitric oxide in the skin raise questions whether the Mediterranean diet works better in sunny regions.
Over the last two decades we have seen a revolution in the value accorded to vitamin D for promoting health. For those of us old enough to remember, vitamin D was once considered as having utility in the prevention of rickets, the prevention of osteoporosis, but for little else.
In the mid 1990s, a careful observer noticed that certain diseases, in particular cancer and multiple sclerosis, have geographical distributions that closely parallels climate related levels of ultraviolet exposure, that is the more sunlight the less disease.  It was assumed that because greater ultraviolet light exposure increases vitamin D levels, that varying vitamin D levels accounted for the differing rates of morbidity. As evidence accumulated that associated low vitamin D levels with higher risk of cancer development and a poorer prognosis, we assumed that taking vitamin D would be protective against getting cancer and would slow cancer growth; not just cancer but a range of other diseases were likely to benefit. People with high vitamin D levels are less likely to have hypertension, diabetes, strokes or heart attacks; they are less likely to die of any cause than people with low levels.
Giving credit to vitamin D for the benefits of sun exposure is attractive as people can take vitamin D in pill form and avoid the necessity and risk of sun exposure, as everyone is quite certain that sunlight is bad for you.
The standard translation of “bad for you” is that the ‘something’ being described shortens one’s life span. But is sunlight really bad for you? Dr. Richard Weller, a Scottish dermatologist, pointed out that there is no evidence that sun exposure shortens life span, writing in a recent opinion piece,
“Ask a dermatologist about the evidence that sunshine raises your risk of dying and there will be an embarrassing silence. After a century of knowing the link between sunshine and skin cancer, this is not good enough. In fact, there is increasing evidence that keeping out of the sun may be killing you – and in more ways than you think….”
Many people now view vitamin D as a panacea, capable of preventing or at least improving all diseases. Perhaps we have become a bit too enthusiastic. Some of the benefits we attribute to vitamin D may come from sunlight itself.
It is unclear whether taking vitamin D is the miracle fix we hoped for. Results of clinical trials in which people took vitamin D have been disappointing. Cardiovascular and metabolic diseases have not responded the way we hoped. A recent clinical trial did not see an improvement in lipid profiles with vitamin D supplementation. Nor does vitamin D improve eczema symptoms in children  or improve asthma as we assumed.  There may be something more to sunlight’s benefits than just increasing vitamin D levels in the body. There are two possible other explanations why sunlight is good for people.
One possible explanation is that sunlight triggers nitric oxide production in the skin. Nitric oxide (NO) causes a range of physical effects in the body but chief among them is vasodilation. The skin stores nitrates and sun exposure triggers their conversion into nitric oxide that in turn lowers blood pressure. As high blood pressure is the leading cause of death in the world, even small improvements in blood pressure can have widespread consequences. This NO discovery explains a long time mystery, why blood pressures are higher during the winter. It also explains why blood pressures increase with latitude.
A 2014 study tells us that ultraviolet light exposure after ingestion of a dose of nitrate improves athletic performance in cyclists. Light exposure alone was not sufficient to do this.  This is likely why people feel better in the sunlight.
This raises some interesting questions. Will taking oral nitric oxide precursors such as l-arginine or beet juice before sunbathing increase nitric oxide production more and so increase health benefits? Or in other words, should we add sun bathing to our list o treatments for cardiovascular disease?
Likewise this nitric oxide business might explain why Waon Sauna therapy is effective in treating congestive heart failure, it mimics sunlight. If you have herpes simplex this idea might backfire though. Increased l-arginine intake and also increases in sun exposure independently increase risk of herpes outbreaks; could this be because both increase nitric oxide?
Perhaps the main issue worth contemplating are the results of the various Mediterranean diet studies, in particular the PREDIMED trial that suggested nut consumption decreases risk for CVD events. Recall that in this large Spanish clinical trial participants supplemented their diet with either nuts or extra virgin olive oil and had significant benefit. Perhaps these cardiovascular benefits were due to the combination of l-arginine in the nuts along with Mediterranean sunlight, which acted together to increase nitric oxide production. If so, is it the combination of nuts plus sunlight that really provided the benefit, not just the dietary intervention alone? Do we need sunlight for the Mediterranean diet to work well?
If this turns out to be true we need to rethink a lot of our recommendations to patients.
There’s another possible explanation why sunlight helps prevent cancer that also has nothing to do with vitamin D production. I wrote about this back in 2007 in an article published in Naturopathy Digest. 
“What may be even more relevant news comes from a study published in the March 9, 2007 issue of Cell, which discloses that the tumor-suppressor gene called p53 is the gene responsible for initiation of tanning. Tanning is a reaction to ultraviolet light exposure. Melanin pigment production is increased and the melanin concentrated in skin cells. Melanin then protects skin cells from DNA damage caused by UV exposure. Researchers had explained most of this tanning process already, but not what initiated tanning. This current paper reveals that UV light activates the p53 gene, which in turn, activates the tanning pathway. Skin cells without the p53 gene will not tan. We typically think of the p53 gene in relation to cancer protection and as the trigger to apoptosis (cellular suicide) of cancer cells. Cells without p53 genes can't protect themselves against cancer. Cells with a working p53 gene usually will kill themselves if they become cancerous. Turning on the p53 gene throu
exposure also may turn on the cancer-fighting potential of both the skin and the body. Sun exposure protects our skin against cancer by stimulating vitamin D production. Sun also may protect against skin cancer by stimulating p53 activity.”
In simpler words, the process of developing a tan triggers activation of a gene called p53 that has an anticancer effect. Finding ways to activate this gene is the goal of one branch of cancer drug development efforts. Here we have a way to activate p53 simply by working on our tans.
Returning to that idea that sunlight is bad for you, there’s an interesting study published in 2014, which followed nearly 30,000 Swedish women recruited in 1990, who had been surveyed and questioned about their sun-seeking behaviors. Two decades later the women who had reported that they did the most sunbathing were half as likely to be dead compared to those who avoided sun exposure.
Non-melanoma vs. melanoma
There are two different types of skin cancer that we must differentiate between when talking about sunlight and health, non-melanoma (or what is often called basal cell) and melanoma. Melanoma is by far the more serious of the two diseases About 74,000 cases of melanoma are diagnosed in the US each year compared to 3.5 million non-melanoma skin cancers. Incidence of melanoma is rising from about 15 cases per 100,000 people per year in 1992 to nearly 22 in 2012. About 8.5% of these cases will prove fatal in the five years after diagnosis. 
Melanoma is more common in indoor workers than outdoor, and in untanned people than tanned people. Episodic sun exposure and sunburn are probably a greater risk factor than continual exposure. Continual sun exposure is the major risk factor for non-melanoma skin cancer. Non-melanoma skin cancers are rarely fatal.  Only about 2,000 (of the 3.5 million diagnosed) people die from non-melanoma skin cancer each year, while 9,940 people (of the 74,000 diagnosed) die every year from melanoma. That’s 0.057% fatality rate for non-melanoma vs. 13.4% for melanoma. This is why we worry more about melanoma, or at least should.
A 2013 paper by Danish researchers suggests that having skin cancer, which is considered an indirect but accurate measure of life time sun exposure, is actually linked with lower risk for several other diseases and overall mortality. The researchers examined data from the entire Danish population who were older than 40 years old from 1980 through 2006, a group of 4.4 million people. Individuals diagnosed with non-melanoma skin cancer had a 4% lower risk for heart attacks [OR 0.96 (95% confidence interval: 0.94-0.98)] and curiously, a 15% increased risk for hip fracture [OR 1.15 (1.12-1.18)]. Risk of hip fracture was reduced (odds ratios were below 1.0) in individuals below age 90 years. This peculiar finding might be explained by the 48% decreased overall risk of death from any cause in those diagnosed with non-melanoma skin cancers [OR0.52 (0.52-0.53)]; there were just a lot more of the skin cancer patients surviving past 90 and getting fractures than in the non cancer gro
Malignant melanoma also offered protection against these conditions and was associated with a 21% lower risk of heart attacks, a 16% lower risk of hip fracture and a 11% reduction in death from any cause. These findings of course as many of my astute readers will remind me if I neglect to point it out, are associations, they do not prove causation. Yet they certainly hint that sunlight might be good for us.  Avoiding exposure may in the long run prove to be the less wise choice.
1. Mohr SB. A brief history of vitamin d and cancer prevention. Ann Epidemiol. 2009 Feb;19(2):79-83.
2. Islam MZ, Shamim AA, Akhtaruzzaman M, Kärkkäinen M, Lamberg-Allardt C. Effect of vitamin D, calcium and multiple micronutrients supplementation on lipid profile in pre-menopausal Bangladeshi garment factory workers with hypovitaminosis D. J Health Popul Nutr. 2014 Dec;32(4):687-95.
3. Galli E, Rocchi L, Carello R, Giampietro PG, Panei P, Meglio 2. Serum Vitamin D levels and Vitamin D supplementation do not correlate with the severity of chronic eczema in children. Eur Ann Allergy Clin Immunol. 2015 Mar;47(2):41-7.
4. Martineau AR, MacLaughlin BD, Hooper RL, Barnes NC, Jolliffe DA, Greiller CL, Kilpin K, et al. Double-blind randomised placebo-controlled trial of bolus-dose vitamin D3 supplementation in adults with asthma (ViDiAs). Thorax. 2015 May;70(5):451-7.
5. Muggeridge DJ1, Sculthorpe N1, Grace FM1, Willis G2, Thornhill L2, Weller RB3, James PE2, Easton C4. Acute whole body UVA irradiation combined with nitrate ingestion enhances time trial performance in trained cyclists. Nitric Oxide. 2014 Oct 5. pii: S1089-8603(14)00451-0.
7. Lindqvist PG1, Epstein E, Landin-Olsson M, Ingvar C, Nielsen K, Stenbeck M, Olsson H. Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort. J Intern Med. 2014 Jul;276(1):77-86.
8. SEER Stat Fact Sheets: Melanoma of the Skin: download June 27, 2015. http://seer.cancer.gov/statfacts/html/melan.html
9. Richard Weller. Shunning the sun may be killing you in more ways than you think
New Scientist. Magazine issue 3025. 15 June 2015
10. Brøndum-Jacobsen P1, Nordestgaard BG, Nielsen SF, Benn M. Skin cancer as a marker of sun exposure associates with myocardial infarction, hip fracture and death from any cause. Int J Epidemiol. 2013 Oct;42(5):1486-96.