In recent years, most of us have heeded dermatologists' warnings and made sun protection a habit, lathering up with sunscreens and avoiding UV exposure in the critical midday hours. But while these protective measures help our skin, they also have us missing out on an essential sun benefit: vitamin D synthesis. New studies on the correlation between low sun exposure and diseases such as cancer and osteoporosis suggest that we may want to reconsider the wisdom of total sun avoidance.
Sun exposure is our primary source of vitamin D, a nutrient that helps the body make use of calcium and phosphorous. Unfortunately, the diligent practice of safe sunning—coupled in colder climates with long winter months of little sun exposure—is leaving people in short supply. "There's no question that, based on photochemistry, we require UV exposure to produce vitamin D in the skin," explains Dr. Michael Holick, Ph.D., M.D., of Boston University Medical Center. "Wearing sunscreen reduces the amount of UV light that reaches the skin by as much as 98 percent." He says that the farther north you live, the less vitamin D you produce, and adds that by age 70, vitamin D production in the body drops down to 30 percent of what it was at age 25. As the body grows sluggish in synthesizing enough of the vitamin, we subsequently absorb less calcium as well.
A lack of vitamin D can result in serious health problems, as researchers are now discovering. Certainly, osteoporosis is a concern, as the vitamin affects calcium absorption. But now it seems there's a cancer link as well. A University of North Carolina at Chapel Hill study showed that men living at high latitudes, and thus exposed to less sunlight, had low vitamin D serum levels and a higher risk of developing prostate cancer than those closer to the equator. Another study conducted by the Northern California Cancer Center revealed a 30 to 40 percent decrease in breast cancer risk among women who were situated in areas of high solar radiation (such as in the South); who had lived longest in sunny climes; who had frequent sunlight exposure; or whose daily dietary intake of vitamin D was 200 IU or more.
So how can we safely increase our vitamin D levels without running the risk of skin cancer? It's as simple as spending 10 to 15 minutes in the sun about three times a week, depending on your skin's sensitivity to sunlight as well as altitude, time of day, and season. Try to get some sun on your face, arms, and tops of your hands—without using sunscreen—in the mid-morning or midafternoon when sunlight isn't too direct. Keep in mind that fairer skin types require less sun exposure to produce the same amount of vitamin D as those with naturally darker complexions, since skin pigments screen out more sunlight.
While as much as 90 percent of our vitamin D supply stems from UV radiation, you can also get some through dietary means (see "Food Sources of Vitamin D"). The National Academy of Sciences recommends 200 IU daily for people under age 50, 400 IU for those age 51 to 70, and 600 IU for people over 70. If you want to take a supplement, it's safest to get your vitamin D in a daily multivitamin form to avoid overdosing.
Ultimately, the best way to ensure your vitamin D levels is to get out and enjoy the sunshine—in moderation. A dose of UV light might be just what the doctor ordered.