A Little Sun
Most experts agree that a moderate amount of sun exposure will help boost vitamin D levels without significantly upping skin-cancer risk. But determining a safe amount is highly personal, and tricky. “There’s no one-size-fits-all recommendation,” says J. Leonard Lichtenfeld, M.D., an oncologist and internist who serves as deputy chief medical officer of the American Cancer Society.
Consider geography, season and weather: if you live in regions north of the midsection of the country, sunlight is too weak throughout fall and winter for you to produce enough vitamin D—and clouds or smog could change the equation any time of year. How old you are is important, as skin becomes less efficient at synthesizing vitamin D as you age; a 70-year-old’s skin produces only one-quarter of the vitamin D that a 20-year-old’s does. If you have dark skin, you’ll produce less of the vitamin, since melanin pigments in skin block the UV rays that start the whole process. When compared to a fair-skinned person, someone with darker skin “may require two to three times the amount of time to make the same amount of vitamin D,” notes Giovannucci.
While there’s no official consensus, a good rule of thumb for a safe vitamin D boost is to aim for 5 to 15 minutes of sun, a few days a week, depending on how sensitive you are to the sun. “No one is advocating burning,” says Heaney.