There a good chance you've adopted at least some of the messages from the media regarding sunscreen and avoiding the sun. But even though a vast body of evidence correlates sun exposure to skin cancer, it's not the cause.

What is lacking in every scientific study ever linking sun exposure to cancer is any evidence that sunlight is actually the cause or that it may shorten our lives. Ask a dermatologist about the evidence that sunshine raises your risk of dying and there will be an embarrassing silence. After a century of so many reports sunshine and skin cancer, there is not one that has conclusively proven that the sun is the culprit. In fact, there is increasing evidence that keeping out of the sun may be killing you -- and in more ways than you think.

Even the most ardent sun-phobes acknowledge that sunlight has health benefits, but these have largely been put down to Vitamin D. People with the highest vitamin D levels tend to be healthier. They are less likely to have high blood pressure, diabetes, strokes or heart attacks -- in fact, they are less likely to die prematurely of any cause. In the absence of Vitamin D from sunlight, disease increases more than 1000 percent.

This raised hopes that a simple vitamin supplement could reduce lots of major causes of death. However vitamin D from sunlight exposure and supplementation may not be interchangeable in terms of effectiveness. Many studies have now tested the effects of vitamin D supplements on health, but the results have been disappointing. The incidences of cardiovascular and metabolic diseases are not reduced by these tablets, and although they can boost bone health and possibly be of benefit against some forms of bowel cancer, vitamin D is not the panacea that many believe. It accounts for some of the sun's health benefits, but not all.
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It's been known that vitamin D can prevent that genetic damage. When vitamin D binds to specific receptors, it sets off a chain of events by which many toxic agents including cancer cells are rendered harmless. However, if there is not enough vitamin D the system can become overwhelmed and cancer can develop. "This is one of the reasons that people living closest to the equator have a much lower incidence (or absence) of specific cancers which consequently increase in locations further from the equator," said McGill University professor Dr. John White.

Sun-produced nitric oxide may also help explain some blood pressure puzzles -- why the average blood pressure of the UK population is lower in summer than winter, for example, and the correlation between latitude and blood pressure, with people living closer to the equator having lower blood pressure than those at higher latitudes.

An increase in nitric oxide in the circulation, which dilates blood vessels and allows more oxygen to get to the muscles tremendously benefits the body.

The dermatology community is hesitant about changing their cautious approach to sunlight exposure, but the wider benefits of sunlight should no longer be ignored. Sunlight is about more than just vitamin D, and nitric oxide may well turn out to be a more important mediator of sunlight's health benefits. Other mechanisms probably also exist.

Too little sun will kill you

But what about skin cancer? How do the risks of developing this disease from sun exposure weigh up against the benefits of UV rays? The results of epidemiological studies set up quarter of a century ago to measure the risks of sunlight are now becoming available. The findings have been surprising.

A survey of 30,000 Swedish women recruited in 1990 and questioned about their sun-seeking behaviour found that the more they had sunbathed, the less likely they were to have died 20 years later. In fact those who did the most sunbathing were half as likely to be dead as those who had avoided the sun entirely. The authors calculate that 3 percent of deaths in Sweden are due to insufficient sun exposure. Other research backs this up. Another Scandinavian study of 40,000 women found that those who went on the most sunbathing holidays were least likely to have died 15 years later.

The primary duty of a doctor is to extend healthy life, not narrowly avoid one disease. In dermatology we have been distracted by what we see -- skin cancer -- and have forgotten what matters most. Vitamin D is often used as a euphemism for "healthy sunlight", but an increasing number of supplementation studies show that the benefits of sunlight cannot all be put down to it. Nitric oxide may be at least as important.

Under the right circumstances, 10 to 15 minutes of sun on the arms and legs a few times a week can generate nearly all the vitamin D we need. Unfortunately, the "right circumstances" are elusive: the season, the time of day, where you live, cloud cover, and even pollution affect the amount of UVB that reaches your skin. What's more, your skin's production of vitamin D is influenced by age (people ages 65 and over generate only one-fourth as much as people in their 20s do), skin color (African Americans have, on average, about half as much vitamin D in their blood as white Americans), and sunscreen use (though experts don't all agree on the extent to which sunscreen interferes with sun-related vitamin D production).

Pale populations have multiplied and have migrated across the earth, many times to geographic regions which are to their disadvantage. Researchers have noted that sunlight and supplements are not the only factors that can determine the level of vitamin D in a person's body.

Lighter skin color allows deeper penetration by UV-B rays, which decreases the amount of sunlight exposure needed for adequate vitamin D production. If you have darker skin, it's harder for UV-B rays to penetrate your skin and create vitamin D, which means that you need greater exposure to sunlight than someone with lighter skin.

Some inherited differences in the way people's bodies process vitamin D into the active form also have a strong effect on people's vitamin D levels.

Vitamin D supplementation or even nitric oxide supplementation will never match natural sunlight and it's time researchers and most of all public health officials started taking a more serious approach to understand how UV exposure benefits the population as a whole and educates the public on safe sun exposure to save lives rather than avoiding under the false assumption that it prevents disease.

Mae Chan holds degrees in both physiology and nutritional sciences. She is also blogger and and technology enthusiast with a passion for disseminating information about health.