Sunlight may help to cut the risk of heart attack and stroke by lowering a person's blood pressure, a study published by Journal of Investigative Dermatology found.

Led by researchers from the Universities of Southampton and Edinburgh, the study examined the skin of 24 healthy participants exposed to ultraviolet (UVA) light from tanning lamps during two sessions, each lasting 20 minutes. In one of the sessions, the volunteers were exposed to both the UVA rays and the lamps' heat. In the other, the rays were blocked and only the heat let through to the skin.

The findings suggested that UVA dilates blood vessels, causing blood pressure to decrease. It also changes the metabolite levels of nitric oxide (NO), a small messenger molecule, in the circulation without changing vitamin D levels.

"NO along with its breakdown products, known to be abundant in skin, is involved in the regulation of blood pressure," said Martin Feelisch, a professor of Experimental Medicine and Integrative Biology at the University of Southampton. "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."

Cardiovascular disease, which is often linked to high blood pressure, accounts for roughly 30 percent of deaths worldwide each year, the researchers note. However, rates are known to vary based on the season and latitude, with the highest levels seen during winter and in countries far from the equator where UV radiation is lower. According to the scientists, the findings are consistent with the seasonal variation of blood pressure and cardiovascular risk seen at temperate latitudes.

"These results are significant to the ongoing debate about potential health benefits of sunlight and the role of Vitamin D in this process," Feelisch said. "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."