For decades now, our sun has been reviled and demonized. The message from the medical community: Avoid direct sun exposure, or face an increased risk of skin cancer. As the American Cancer Society helpfully put it in one ad campaign: "Fry Now. Pay Later."
The American Academy of Dermatology recommends never exposing bare skin to the sun, or even a cloudy sky, without sunscreen. The Food and Drug Administration calls ultraviolet radiation a carcinogen. These messages have caused widespread paranoia about sunlight, especially among parents who religiously apply sun protection multiple times a day on their children.
But just as we need to avoid cancer, we also need vitamin D, and the sun is the only reliable way to get it outside of a daily supplement. Australia's decades-long public campaign to curb its skin cancer rates and encourage less sun exposure has been unfortunately effective: 31 percent of Australian adults are now vitamin D deficient, which is linked with a number of serious and deadly conditions, including several cancers. Sunscreen dramatically affects the production of vitamin D during sun exposure — SPF 30 reduces it by 97 percent.
I suggest to my patients that they go out in the sun between 10 a.m. and 3 p.m. (very little if any vitamin D is produced outside those hours) for half the time it would take them to develop a mild sunburn — while covering the face and hands with sunscreen but leaving other parts of the body exposed. After this exposure, I urge them to use sun protection to prevent burning.
Vitamin D has crucial functions. It's actually a hormone, and its active form is responsible for regulating the absorption of dietary calcium and phosphorus, two nutrients essential for bone health and neuromuscular activity. Vitamin D also regulates cellular growth, keeping cells healthy and helping to prevent them from becoming malignant.
It would be wrong and foolish, of course, to say that sun exposure isn't dangerous. Excessive exposure to the sun damages DNA in skin cells, which in turn can cause non-melanoma skin cancer. Solar UVA radiation produces free radical oxygen, a potent oxidant, in the skin, leading to wrinkles and damage; it also depresses immune reactions that normally destroy developing skin tumors, resulting in increased risk for both nonmelanoma and melanoma skin cancers.
More than 3.5 million skin cancers are diagnosed in more than 2 million people in the United States annually. An estimated 1 in 5 Americans will develop skin cancer in their lifetimes. So this is not insignificant.
But proper exposure to the sun, and the subsequent increased vitamin D, is good for you. The USDA's 2015 Dietary Guidelines Advisory Committee placed vitamin D high on its list of underconsumed nutrients; it also identified vitamin D deficiency as a public health threat. There are few dietary sources for vitamin D, which means we must rely on the sun, just as our hunter-gatherer ancestors did.
Faced with high cancer rates, health authorities have rushed to damn the sun without taking into account the many scientifically documented health benefits it provides. Along the way, the danger of sun exposure has been exaggerated. Of the estimated 13,000 deaths associated with skin cancer each year, more than 70 percent are due to melanoma, which accounts for less than 5 percent of all skin cancers. Most melanomas occur on the least sun-exposed parts of the body, such as the buttock, the upper arms and the back of the legs. People who work outdoors actually have lower incidences of melanoma, despite spending significantly more time in the sun than office workers.
The recommendation to avoid sunlight is based on the premise that this reduces the risk of skin cancer, including the most deadly form, melanoma. Yet abstinence hasn't worked: Skin cancer rates continue to increase unabated, and vitamin D deficiency — and the many ills associated with it — is rising. Health care organizations need to recognize, as the World Health Organization does, that small amounts of UV are beneficial and essential to the production of vitamin D. The sun, used sensibly, is not to be feared.
Michael F. Holick is a professor of medicine, physiology and biophysics at Boston University Medical Center.
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