The good and bad on sun exposure

There’s plenty of public awareness about the dangers of skin cancer, but much less about the benefits of sun exposure. Our skin isn’t just a passive, inert covering. Taking in sun allows the body to manufacture vitamin D, and more recent research suggests that when exposed to sunlight, skin helps regulate blood pressure.

It’s possible that current recommendations to stay out of the sun might be counterproductive for darker-skinned people, who are at lower risk for skin cancer and higher risk of hypertension.

In the U.S., African-Americans are much more likely than white, Asian or Hispanic-Americans to have hypertension, and they suffer a disproportionate risk of heart disease and strokes. Doctors have examined many potential explanations – stress, diet, genes – and one long overlooked is looking increasingly likely: lack of sun exposure.

Scientists have found that people with higher vitamin D levels have lower blood pressure, but some now think that the vitamin D isn’t the main driver of blood pressure, but rather that sunlight regulates vitamin D and blood pressure through separate mechanisms. In which case, vitamin D supplements won’t serve as a complete substitute for sunshine.

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Salt was long considered the main high blood pressure culprit because it can raise blood pressure to dangerous levels in people who already have chronic hypertension. But it’s not clear salt causes the chronic problem in the first place.

Skipping sunscreen is not the answer.

The connection between sun exposure and blood pressure cropped up last month in a widely shared story for Outside Magazine headlined, “Is Sunscreen the New Margarine?” The story compared “slavish application of SPF 50” to “Marlboro 100s.” This is misleading because Marlboros and margarine are bad for people, while sunscreen can be good for some people to use some of the time.

The piece inspired a backlash, and failed to convince me to skip sunscreen, but what caught my interest was a secondary theme – the suggestion that current recommendations for sun avoidance are racist. There’s no evidence of outright malice behind the advice. It’s quite likely simply a product of skin doctors tending to focus on skin diseases; blood pressure is for other specialties.

From an evolutionary perspective, human skin was well-adapted to sunny Africa. Lighter skin evolved as a partial adaptation to higher-latitude living – allowing people to get more vitamin D with less sun. But none of us are perfectly adapted to live where winters are cold and dark.

Penn State anthropology professor Nina Jablonski is the author of “Skin: A Natural History.”

She said that skipping sunscreen is not the answer. Anyone, no matter what color, can suffer damage to DNA in skin cells if you live indoors high in the Northern Hemisphere most of the winter, then suddenly jet off to Mexico or Costa Rica and don’t protect your skin. Sudden shocks appear to be worse than steady exposure: People who work outdoors are less likely than office workers to get deadly skin cancer. But not all of us are cut out for outdoor jobs. And while deadly skin cancers are rare, the nondeadly kind can be complicated to remove, especially from faces.

There’s likely to be a sweet spot for sun exposure, Jablonski said, which would balance out the risks and benefits. That spot will be different for darker-skinned people than for those with medium skin tones, and different still for the very fair. And yes, she said, a need for more sunlight might at least partly account for the fact that African-Americans suffer disproportionately from ­hypertension.

Perhaps someday the much-maligned tanning bed will be reconceived in a responsible form, optimized to improve blood pressure and help stimulate natural vitamin D production. And for that winter vacation or ski trip, there will still be a place for sunscreen.

Faye Flam is a Bloomberg Opinion columnist.