Published: June/July 2009
The Sun Rx
The more SPF the better, right? Maybe not. Turns out some 'screen-free time outdoors may be just what the doctor ordered.
Text by Kate Rope

Just three miles into the Olympic marathon in Beijing last summer, American record-holder Deena Kastor, 36, felt a pop in her right foot and dropped to the ground in pain from a broken metatarsal. The cause: A deficiency in vitamin D had weakened her bones.

Three out of four Americans today aren’t getting enough vitamin D, and the ramifications could be severe. A deficit has been linked to everything from cancer to diabetes, osteoporosis, and heart disease. Numerous studies have shown the benefits of D: It aids calcium absorption, keeps us agile as we age, and may fend off colds. It could even make us better athletes, improving reaction time and building muscles.

And while one eight-ounce serving of orange juice is all you need to get your daily fill of vitamin C, to get enough D you’d need to drink ten tall glasses of milk or eat seven pounds of wild salmon—every single day. “There is essentially no vitamin D in your diet,” says Michael F. Holick, M.D., Ph.D., a professor of medicine at Boston University. His surprising solution? Embrace the sun again—sans sunscreen.

Our body synthesizes vitamin D naturally when exposed to sunlight, but high-SPF lotions block the ultraviolet rays needed for its production. The UV triggers a form of cholesterol in our skin that is converted into D in our kidneys. This is where Kastor weakened her system. A skin cancer survivor, she is religious about sun protection. “I was so surprised that my effort to be healthy caused damage in another way,” she says. Now recovered, Kastor relies on daily D supplements—and hasn’t been injured since.

“Different skin types and diets make everyone’s sun needs unique,” says Robyn Lucas, M.D., Ph.D. But generally, “short sun exposure of more skin is a lot safer than longer exposure of just your face and hands.” Even the American Cancer Society is getting on board, recently issuing a joint statement with the Canadian Cancer Society that concluded “supplementation and small amounts of sun exposure are the preferred methods of obtaining vitamin D.”

Still, time in the sun is never safe for some. If you have a fair complexion or a family history of skin cancer, stick to nonsolar sources. Also, if you have dark skin (which, like sunscreen, impedes vitamin D synthesis), aim to get 1,000 international units (IU) a day through supplements. Most multivitamins contain only 400 to 600 IU of D, so add an extra tablet of pure vitamin D to your daily intake. Popping pills is definitely easier than finding new ways to cook up seven pounds of salmon every day.

“D” is for dynamo: Some surprising benefits

· Adolescent girls with higher levels of vitamin D have stronger muscles and can jump higher than their peers, a University of Manchester study found.

· Adequate levels of vitamin D could significantly cut your risk of cancer, according to a Creighton University study.

· Vitamin D deficiency may increase the risk of cardiovascular disease, a study by the American Heart Association concluded.

The Science of Sunbathing: Get all the Vitamin D you need with some well-timed summer sun

3 to 10 minutes of sun exposure with 40% of your skin bared, twice a week during the summer, is enough to get almost a year’s worth of D. (If you’re out any longer than that, apply sunscreen.)

The Greenscreen

Soléo Organics SPF 30+ protects skin without coral-reef-bleaching chemicals ($20 for 2.6 oz).