Scientists have known for years that rates of hypertension are higher in the winter and in countries farther from the equator, but they haven’t known why—until now. A new study from the universities of Southampton and Edinburgh suggests that exposure to sunlight plays a large role, by causing nitric oxide in the skin to be absorbed into the blood stream. Blood vessels widen as a result, causing a modest—but potentially life-saving—drop in blood pressure.
To study the sun’s effect on blood pressure, researchers exposed 24 healthy volunteers to ultraviolet light, mimicking the amount of exposure a person might get wearing short sleeves and shorts outside for 30 minutes on sunny day. In a second session, they were exposed to the same amount of light and heat, but no UV rays.
The UV exposure triggered a small decline in blood pressure—about two to five points—while the “sham” exposure did not. While that may not seem like a lot, the authors write that a even tiny drop can go a long way: A 10-point change in diastolic pressure, for example, can slash your risk of cardiovascular disease and stroke in half.
We should still be concerned, of course, about the very real risks of skin cancer. But the study also notes that mortality rates from melanoma are much lower, worldwide, than those from heart disease or stroke. “Avoiding excess sunlight exposure is critical,” says coauthor Martin Feelisch, Ph.D. “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.”
What the authors don’t know is whether repeated UV exposure can reduce blood pressure even further and if its effects are similar for people of different ages and with different health issues. If future research produces positive results, they say, changes to public health recommendations may be in order.
For now, says study coauthor and dermatologist Richard Weller, consider your individual risk factors when heading outdoors: People with red hair, a family history of melanoma, or skin that burns easily should take extra care in the sun. “The rest of the population shouln’t worry so much,” he says; “the health benefits of sunlight are huge.” (People with high blood pressure, he adds, should still see a doctor—not self medicate with tanning booths or afternoons by the pool.)
Bottom line: Don’t overdo your time in the sun—and wear sunscreen to avoid getting burnt—but don’t hide from it altogether, either.