Date Published: 20 January 2014

The effect of sunlight on (reducing) blood pressure

Researchers at Southampton University (England, UK) in collaboration with researchers at Edinburgh University (Scotland, UK) have recently published new work suggesting that exposing skin to sunlight may help to reduce blood pressure - which could, in turn, reduce the risk of heart attacks and strokes. (For more about the link between high blood pressure and heart problems see heart disease risk factors.)

The mechanism by which the researchers have suggested that exposure to sunlight might help to reduce blood pressure involves the effect of the small messenger molecule, nitric oxide (NO). It has been suggested that sunlight on the skin might affect the levels of NO molecules in the skin and blood, resulting in a reduction in blood pressure.

Although medical experts have recommended limiting skin exposure sunlight in order to reduce the risk of developing skin cancer, the authors of the recent study suggest that reducing exposure to sunlight too much might be unwise because that could increase the risk of developing certain conditions associated with cardiovascular disease. Cardiovascular disease, which is often linked with high blood pressure (also known as hypertension), has been said to account for around 30% of deaths globally each year. Details of this are complicated by the facts that blood pressure and cardiovascular disease vary with season and latitude, higher levels being observed during the winter months and in countries further from the equator, where ultraviolet radiation (UV) from the sun is lower.

Martin Feelisch, a Southampton University Professor of Experimental Medicine and Integrative Biology, said:

"NO along with its breakdown products, known to be abundant in skin, is involved in the regulation of blood pressure. When exposed to sunlight, small amounts of NO are transferred from the skin to the circulation, lowering blood vessel tone; as blood pressure drops, so does the risk of heart attack and stroke."

During the study, the skin of 24 healthy individuals was exposed to ultraviolet (UVA) light from tanning lamps for two sessions of 20 minutes each. In one session, the volunteers were exposed to both the UVA rays and the heat of the lamps. In another, the UV rays were blocked so that only the heat of the lamps affected the skin.

The reported results suggest that UVA exposure dilates blood vessels, significantly lowers blood pressure, and alters NO metabolite levels in the circulation, without changing vitamin D levels. Further experiments indicate that pre-formed stores of NO in the upper skin layers are involved in mediating these effects. The data are consistent with the seasonal variation of blood pressure and cardiovascular risk at temperate latitudes.

Professor Feelisch added:

" These results are significant to the ongoing debate about potential health benefits of sunlight and the role of Vitamin D in this process. It may be an opportune time to reassess the risks and benefits of sunlight for human health and to take a fresh look at current public health advice. Avoiding excess sunlight exposure is critical to prevent skin cancer, but not being exposed to it at all, out of fear or as a result of a certain lifestyle, could increase the risk of cardiovascular disease. Perhaps with the exception of bone health, the effects of oral vitamin D supplementation have been disappointing.
_We believe that NO from the skin is an important, so far overlooked contributor to cardiovascular health. In future studies we intend to test whether the effects hold true in a more chronic setting and identify new nutritional strategies targeted at maximizing the skin's ability to store NO and deliver it to the circulation more efficiently."

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