Sun Exposure Benefits May Outweigh Risks Say Scientists
In the landmark study, the researchers found that when sunlight touches our skin, a compound called nitric oxide that helps lower blood pressure, is released into our blood vessels.
Richard Weller, Senior Lecturer in Dermatology, and colleagues, say the effect is such that overall, sun exposure could improve health and even prolong life, because the benefits of reducing blood pressure, cutting heart attacks and strokes, far outweigh the risk of getting skin cancer.
The proof-of-principle study is being presented this week in Edinburgh at International Investigative Dermatology 2013, the world's largest gathering of skin experts.
The abstract was published online in the Journal of Investigative Dermatology on 15 April.
The researchers note that rates of high blood pressure and cardiovascular disease rise in winter and are tied to geographic latitude (for instance they are higher in northern Europe than in southern Europe).
Also, estimates show that in northern Europe, for every death from skin cancer, about 60 to 100 people die of stroke and heart disease linked to high blood pressure.
This new study is important because until now it was thought that sunlight's only benefit to human health was production of vitamin D, which rises after exposure to the sun.
Previous studies have found that while increased vitamin D levels link to lower cardiovascular disease, oral supplements do not have an effect on this.
Weller and colleagues found that the body's production of nitric oxide is separate from production of vitamin D.
For their study they invited 24 volunteers to sit under sunlamps for two 20 minute sessions while they examined their blood pressure.
In one session, they exposed the volunteers to both ultra-violet (UV) rays and heat from the lamps. In the other session, they only exposed them to the lamps' heat and blocked the UV rays.
The results showed that the volunteers' blood pressure fell and their heart rate rose in the session where they were exposed to both UV and heat, but not when they were exposed to heat only. The reduction in blood pressure lasted for about 50 minutes.
Human skin contains large stores of nitrite (NO2) and nitrate (NO3). The researchers note that while nitrate is "biologically inert", the action of sunlight can reduce it to active nitrite and nitric oxide (NO).
They found that circulatory nitrate fell and nitrite rose during UV and heat exposure, but not during exposure to heat only. There was no difference in vitamin D levels.
Weller says in a statement that:
"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."
He and his team now want to look at the relative risks of skin cancer and heart disease in people who have received different amounts of exposure to sunlight.
"If this confirms that sunlight reduces the death rate from all causes, we will need to reconsider our advice on sun exposure," says Weller.
There have also been suggestions that exposure to the sun can help prevent infectious disease. For example, in 2011, Phil Rice, a virologist at St George's Hospital, University of London, suggested that the sun's UV rays inactivate the chickenpox virus on the skin.
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"UVA lowers blood pressure and vasodilates the systemic arterial vasculature by mobilisation of cutaneous nitric oxide stores";
D Liu, BO Fernandez, NN Lang, JM Gallagher, DE Newby, M Feelisch and RB Weller; Journal of Investigative Dermatology (2013)
133, S209–S221, abstract no 1247, published online 15 April 2013; DOI:10.1038/jid.2013.104.
Additional source: University of Edinburgh.
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