What if avoiding the sun is bad for your health?
It was around 15 years ago that Dr. Matt Zirwas, an Ohio-based dermatologist, first noticed something curious about the people he was treating at his clinic.
“The older patients I was seeing [who had] lots of sun damage and lots of skin cancer would be very robust, very energetic people,” he says. These were people who, apart from their skin cancers, tended to be in excellent health and taking very few prescription drugs.
“But then I’d see these people who had beautiful skin and no cancers, and they were very low-energy and taking medications for all these different health problems,” he recalls. He began to wonder whether exposure to ultraviolet (UV) light, mostly from the sun, had more health benefits than he and other experts realized.
When most people consider UV light and its effects, skin cancer and premature aging come to mind. And there’s no question that exposure to the sun, tanning beds, and other sources of UV light damages the skin in ways that promote aging and cancer. That’s why most dermatologists and public health officials recommend that Americans slather sunscreen on exposed skin whenever they leave the house — even in the wintertime — or take other steps to avoid sun exposure.
“The standard line from dermatologists is that no part of your skin should ever be exposed to unprotected sun,” Zirwas says. “And I agree that if you’re talking about preventing skin cancer and aging, you want to avoid the sun.” But his clinical observations made him wonder whether the story on UV light was really all negative, and if a zero-tolerance policy on sun exposure was warranted when taking a broad view of human health.
“We evolved as outdoor creatures who were exposed to the sun, so it never made sense to me that sun exposure would be all bad,” he says.
Zirwas started reading the published literature on UV exposure and human health. In 2014, a study appeared that Zirwas says changed his thinking from “this is all kind of interesting” to “holy shit!”
That study was published in the Journal of Internal Medicine, and it examined 20 years of health data collected from nearly 30,000 Swedish women. The data included questionnaires that asked women about their sun habits, as well as about their smoking history, alcohol use, body weight, education level, income, and other variables that tend to raise or lower a person’s risk for death.
The study found that the risk of death from all causes approximately doubled among women who tended to avoid the sun compared to women who got the greatest amount of UV exposure — including from both the sun and from tanning beds.The relationship was dose-dependent, the study found, meaning that the more sun a woman reported getting, the lower her risk of death. The protective effect of sun exposure remained significant, even after the study authors adjusted their figures for income, BMI, smoking history, and other factors that could account for their findings.
“If that study’s findings are correct,” Zirwas says, “that means protecting yourself from ultraviolet light could have the same effect on your mortality as deciding to smoke a pack of cigarettes a day.”
“That study,” he adds, “made me say, ‘Oh my God, there has to be a lot more to this story.’”
A case for sun exposure?
Heart disease is the most common cause of death in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC). And that study from Sweden found that a drop in heart-disease deaths among the sun-exposed women was the most significant contributor to their lower mortality rates.
Mel, 43, no sunscreen. “Black is beautiful!”; Myrtle Beach, South Carolina. Photo by Jacq Harriet
It’s not the only study that has drawn ties between sun exposure and improved heart health. For decades, researchers have observed what they call the “winter cardiovascular disease phenomenon.” Both in the United States and in Europe, heart disease-related deaths peak in winter and bottom-out in summer, and the swing is not subtle. There’s also evidence that some markers of heart disease rise fairly consistently among people as their location slides farther north or south of the equator.
Experts have hypothesized that the presence or absence of UV light could account for these discrepancies. But there are also non-UV explanations. Exposure to cold temperatures, for example, tends to constrict blood vessels, which could explain some of these phenomena. But, during the past decade, several papers have come out that argue a “sunshine deficit” is a likely contributor to heart disease, and that sunlight has cardiovascular benefits independent of its ability to stimulate vitamin D production. (More on vitamin D in a minute.)
Some of this research has come from Dr. Richard Weller, a dermatologist at the University of Edinburgh in Scotland. “Without a shadow of a doubt, sun exposure is a risk factor for skin cancer,” Weller says. “But the question is, what is the risk-benefit ratio of sun exposure? Where is the evidence that sun exposure shortens life?” Weller says that this evidence does not exist. Along with the pro-sun Swedish study, he cites a large study from Denmark that found people who had been diagnosed with skin cancer actually experienced lower rates of heart disease and death compared to the general population.
How could skin cancer be associated with a reduced risk of death? A dig through the skin cancer stats yields some surprises.
Skin cancer is by far the most common type of cancer in the United States, according to the CDC. And for those who develop melanoma, skin cancer is serious and sometimes lethal. But the vast majority of skin cancers — roughly 99% — are non-melanoma basal cell and squamous cell cancers. Of these, roughly 80% are basal cell cancers (BCCs). While removing BCCs can be a painful procedure and one that results in significant scarring, these cancers are almost never deadly. These are also the skin cancers most closely associated with sun exposure, and that commonly show up on a person’s hands, scalp, and other sun-exposed areas, according to the American Cancer Society (ACS).
Even if sun exposure were the sole cause of all skin cancers, which is unlikely, the lethality of the disease is far lower than one might assume. The American Academy of Dermatology estimates that melanoma will kill 7,230 people in the United States this year, while other forms of skin cancer will claim another 4,420 lives. Cardiovascular disease, meanwhile, kills approximately 650,000 Americans each year, per the CDC. Both Zirwas and Weller argue that if sun exposure offers even modest protection against heart disease, the benefits of sun exposure could quickly outweigh its risks.
Heart experts say this argument has some merit. “The idea that sunlight is good for our hearts makes a lot of sense,” says Dr. James O’Keefe, a cardiologist at Saint Luke’s Mid America Heart Institute in Kansas City, Missouri. Studies have shown that exposing skin to UV light triggers the release of nitric oxide in the blood, which results in a drop in blood pressure. “Nitric oxide keeps vessels soft and supple, and it gives them a Teflon-like surface so platelets don’t stick,” O’Keefe says. “And when skin is exposed to sunlight, nitric oxide is released into the bloodstream in pretty large amounts.”
UV exposure could benefit the heart in other ways. “Sunlight leads to the release of the chemical serotonin, whose effects include expansion of blood vessels that, in turn, can help to reduce blood pressure,” says Dr. Michael Miller, director of the Center for Preventive Cardiology at the University of Maryland School of Medicine. Miller says he recommends that the people he sees get 10 to 15 minutes of daily sun exposure “One thing that is astounding about modern life is that most of us spend most of our time indoors, and when we go outside, many of us protect ourselves against the sun,” says Nina Jablonski, a biological anthropologist at Penn State University. This is vastly different from the way human beings lived even 100 years ago, when many people worked in farming or other predominantly outdoor occupations. “So the combination of these things — our indoor lifestyle and taking some precautions against sun exposure — means many of us have almost zero sun exposure and zero ability to make vitamin D through our skin.”
Jablonski says every human being’s skin has adapted to the type of sun exposure their ancestors endured. This adaptation — calibrated to specific latitudes and levels of ultraviolet radiation — offered their ancestors protection from sun damage while allowing in enough UV light to facilitate vitamin D production and other important biological processes.
While people of Northern European ancestry who have pale skin tend to suffer from high rates of skin damage and skin cancer if they live in places near the equator, Hispanics and people of African ancestry who move into more temperate regions may suffer due to the lack of sun exposure, she says. Some researchers have even postulated that low vitamin D levels among African Americans could help explain in part why, in America, they are more likely than white people to die from heart disease, stroke, diabetes, and some cancers.
I think dermatologists want people to have skin that is healthy and cancer-free for as long as possible,” Jablonski says. “But most aren’t looking past the skin — they’re not thinking about the global well-being of their patients.” While she doesn’t believe that taking a vitamin D supplement can fully replace the health benefits of sun exposure, she says it’s one measure that research has linked with improved health outcomes.
But others disagree with her on this point. “Everyone gets utterly fixated on vitamin D, but when you give people vitamin D supplements, the only thing that has been shown categorically is that it’s good for bone health,” says the University of Edinburgh’s Weller.
His take is largely supported by the recently completed VITAL trial, which measured the effect of long-term vitamin D supplementation on the health outcomes of more than 25,000 American adults. That trial found that people who took a daily 2000-IU vitamin D supplement for five years did not experience a significantly reduced risk for heart attack, stroke, or death due to cardiovascular disease or all causes.
“The randomized controlled trials on vitamin D supplementation have generally been disappointing,” says Dr. Joann Manson, who led the VITAL trial and is chief of the Division of Preventive Medicine at Brigham and Women’s Hospital in Boston. Manson is quick to note that vitamin D is very important to heart health. It’s just that people don’t need much of it, and very few Americans are so deficient in vitamin D that their heart health is suffering for it, she says.
Weller argues that Vitamin D is just a marker for sun exposure, and that many of the studies linking low vitamin D status to poor health outcomes are really evidence that a lack of adequate sun exposure is harmful to human health. “People assume that vitamin D is responsible for all the benefits of sunshine, and the standard advice from dermatologists is all about avoiding sunshine and taking a vitamin D supplement,” he says. “But there are probably lots of pathways by which sunlight exerts beneficial effects.”
Looking beyond heart disease, research has uncovered associations between higher levels of sun exposure and reduced rates of Type 2 diabetes. There’s also evidence linking sun exposure to a lower risk for some non-skin cancers. A 2013 study from the National Cancer Institute found that people who lived in places with high levels of sun radiation experienced an uptick in risk for melanoma, but a drop in risk for cancers of the colon, lungs, prostate, bladder, kidney, and blood. Overall, UV radiation exposure showed “a significant inverse association with total cancer risk,” the study’s authors wrote.
Meanwhile, there’s evidence — both positive and negative — linking UV light exposure to immune function. Some studies have found that sunlight suppresses aspects of immune function, and that it can trigger or worsen symptoms among people with autoimmune disorders such as lupus. On the other hand, studies have found a link between greater sun exposure and lower rates of allergies, asthma, and autoimmune disorders, such as multiple sclerosis, Type 1 diabetes, and rheumatoid arthritis. Researchers have even postulated that humanity’s move indoors and away from the sun could explain the exploding rates of autoimmune disease.
Sunlight also affects the way people think and feel. Research has linked UV exposure to mood and well-being benefits, and to lower levels of depression.
All this lends credence to “sun is good for you” arguments. But nearly all of this research is preliminary and in need of follow-up. Experts also point out that it’s tricky to separate the benefits of sun exposure from related and confounding variables. “People who are outdoors and who get a lot of UV exposure also tend to be physically active, which we know has health benefits,” Manson points out. Some of the research linking sun exposure to improved health outcomes has controlled for a person’s exercise habits and other factors. “But,” Manson says, “it’s still very, very difficult to disentangle a lifestyle associated with greater UV exposure from the specific effects of UV exposure.”
At the same time, she says treating the sun like an enemy is probably taking things too far. “I’m sure that moderate exposure to the sun is perfectly compatible with a healthy lifestyle,” she says.
Balancing the risks and benefits
It’s reasonable to argue that the established connection between UV radiation and skin cancer should, at this point, outweigh the unsubstantiated benefits of sun exposure. And this argument has largely won over public health authorities.
“It’s hard to counsel people on a theoretical benefit versus a risk we absolutely know exists,” says Dr. Hayley Goldbach, a dermatologist at UCLA Health. “At this point, in 2019, I think we can say applying sunscreen and avoiding UV radiation, and also taking a vitamin D supplement, is the best way to mitigate health risks.”
But others say this line of thinking overestimates the real harms of sun exposure while underplaying its likely benefits. “Orthopedic surgeons don’t go around telling people not to exercise because it will lead to all these knee surgeries when they’re 70,” Weller says. “They recognize that the benefits of exercise are hugely greater than the risks, but dermatologists don’t seem to be able to do this equation [when it comes to sunlight].
“All this seems a bit left field to some, but when you look at the environment in which human beings evolved, it’s certainly abnormal to be avoiding sunlight,” he says.
At the same time, he says UV exposure isn’t a panacea. He says people should take steps to avoid sunburns — steps that include wearing sunscreen when spending a lot of time outdoors. But, he adds, one of the problems with medicine (and with medical journalism, for that matter) is that things tend to be categorized as “good” or “bad,” and the reality is usually far more complex.
“It’s hard to convey the risks and benefits of sun exposure in a public health context,” agrees PSU’s Jablonski. “People want simple messages and one-size-fits-all advice, but what’s emerging is that we have to think about ourselves as individual cases.” She says advice to avoid all unprotected sun exposure is “an imbalance that needs to be righted.” But the optimal amount of sun exposure is going to vary depending on a person’s location, the time of year, their age, their ability to tan — as opposed to burn — and other factors.
O’Keefe, the Saint Luke’s cardiologist, agrees with these takes. “If you’re blue-eyed and from Scandinavia, it doesn’t make sense to go lie out in the sun in Miami,” he says. “Evolutionarily, it’s not what you’re prepared for.” But all of us need some sun, he adds. “To hide inside like a mole and avoid sun exposure, I think that’s just a recipe for depression and poor health.”
Zirwas, the Ohio dermatologist, takes things a bit further. He says he advises his patients to apply sunscreen or take whatever other precautions are necessary for them to prevent blistering or peeling sunburns, which he says are the “biggest worry” when it comes to skin cancer. These precautions “will vary massively depending on the person and the conditions, but most people know what it would take for them to burn,” he adds.
But short of burning, he says he has no problem with people developing a tan — a position that would likely outrage many of his fellow dermatologists. “I think the benefits of [non-burning] sun exposure far outweigh the skin-cancer risks,” he says.
“If you’re worried about aging, put sunscreen on your face and hands,” he says. “But the idea that we should get no UV at all — we should be debating this.”