If we find that people who get more sun die sooner of any cause, then we absolutely need to tell people to be very cautious. If, on the other hand, we find that people who get less sun have increased all-cause mortality, that’s a game changer.
Dr Richard Weller
Research due to be presented tomorrow at the International Investigative Dermatology conference in Edinburgh suggests that the benefits of exposing your skin to sunlight could outweigh the risk of developing skin cancer. The study contends that by lowering blood pressure, sunlight reduces the risk of heart disease, heart attack and stroke.
Exposure to sunlight causes the release of a compound into the blood which causes the blood vessels to dilate, the researchers found, thus reducing blood pressure, improving overall health and possibly even prolonging life. This mechanism is not associated with the production of vitamin D, which also rises after the skin is exposed to sunlight.
In an interview with ScienceOmega.com
, lead researcher and senior lecturer in dermatology at the University of Edinburgh, Dr Richard Weller, explained that he did not set out to investigate the health benefits of sunshine. His research focus was the role of nitric oxide in the skin and he had initially been looking at its effects on skin cell death after sunlight exposure. Efforts to replicate results from mouse studies revealed surprisingly large stores of nitric oxide in human skin.
"Nitric oxide (NO) itself is a gas and quickly disappears, but we found nitrite (NO2
) and nitrate (NO3
) in the skin," Dr Weller noted. "These are more stable, non-gaseous forms of NO and can therefore linger in the body.
"The skin harbours significant stores of nitrite and nitrate; we found that sunlight has the effect of turning these back into NO which then moves from the skin into the bloodstream. In the bloodstream, NO dilates the blood vessels and thereby lowers blood pressure."
Benefits at a population level?
In one of their experiments, the researchers studied the effects of two, 20 minute sessions under tanning lamps on 24 volunteers. In one session, they were exposed to ultraviolet (UV) light and heat from the lamp, while in the other the UV rays were blocked out. The team recorded a significant drop in blood pressure for one hour after the session, but only when the participants had been exposed to UV.
Since heart disease and stroke are estimated to be responsible for approximately 80 times more deaths than skin cancer in the United Kingdom, the results could have implications for public health if this effect proves extensive in further studies.
"Blood pressure is one of the major risk factors for early death in terms of heart disease and stroke, which are the big killers in most of Europe and the developed world," said Dr Weller. "Although the blood pressure changes recorded in the experiment were small – not enough to make a big difference to one individual with hypertension – there could be benefits at a population level."
While it is often assumed that the health benefits of sunlight are entirely mediated by vitamin D, volunteers’ levels of the vitamin were shown to be unaffected in these experiments. It has been known for many years that sunlight has the effect of lowering blood pressure, too, but Dr Weller and his colleagues have demonstrated a previously unknown mechanism by which it does so.
Health message remains the same
Dr Weller does err on the side of caution, however, when it comes to the idea of throwing out the sunscreen this summer. The findings do not negate the fact that sunlight is, without a shadow of a doubt, the major alterable risk factor for skin cancer and that the best way of reducing your risk of skin cancer is to not get too much sunlight.
"Our sample was just 12 or 24 people depending on which experiment you’re looking at, and a one-off dose of UV lowered their blood pressure for an hour," he said. "That’s not going to be enough to stop them dying young. It shows that the mechanism exists, but it doesn’t say this is something we should be rushing out and doing now.
"The health message remains the same as it always was because all of the work that has been done on sunlight and skin cancer is solid, thorough and extensive. This has been four years’ work, but it’s a drop in the ocean compared to that body of research. I hope this is the start of something much bigger, but the standard public health message remains that no-one, particularly children, should get sunburnt."
I asked Dr Weller if there are other ways that people could gain the exposure to UV light needed to keep them healthy without putting themselves at risk of developing skin cancer.
"The ideal would be to get enough sunlight to lower your blood pressure and risk of stroke without causing skin cancer," he responded. "Is there a sweet spot we can hit? How does this vary with different skin types? These are important questions, but at the moment we don’t know the answers."
Dr Weller suggests the hypothesis that the unintended consequence of protecting ourselves from sunlight in order to reduce the risk of skin cancer might be that the risk of death from other causes increases. As he stressed, however, it is not yet possible to say so and much more work will be needed to prove definitively that the benefits of sunlight outweigh the risks.
"We’re applying for funding for a study to see whether a long-term, useful reduction in blood pressure can be produced when people receive a dose of UV light every day," he told me.
First on the agenda, however, is to try to answer the question of how the amount of sun a person gets impacts on other causes of mortality.
"We’re applying for access to the UK Biobank which recruited half a million people to a huge prospective study between 2006 and 2010. We want to see how people’s sunlight behaviour affects not just skin cancer but death by any cause. If we find that people who get more sun die sooner of any cause, then we absolutely need to tell people to be very cautious. If, on the other hand, we find that people who get less sun have increased all-cause mortality, that’s a game changer."