21st Century Health Hazards Everyone Should Know About
The Danger: Even though doctors have been talking about vitamin D deficiency for years now—how it's linked to osteoporosis, possibly certain cancers and lowered immunity—a lot of us are still getting too little of it. (We're more careful about sun exposure which affects levels, explains Edward Giovannucci, MD, professor of nutrition and epidemiology at the Harvard School of Public Health, who also notes that obesity seems to lower vitamin D levels.)
Your Safety Plan: Since we produce vitamin D in response to sun exposure, soaking up sunshine would help. It's not that simple though, because there's limited research on how sunscreen affects the process. An often-cited JAMA Dermatology study found no difference in vitamin D levels between people who were using sunscreen for one summer and people unknowingly applying a placebo instead. Here's the rub: It was a small study, and the experimental group was only using SPF 17 (the American Academy of Dermatology recommends a minimum of SPF 30, which blocks a greater percentage of rays, to reduce the risk of skin cancer). Sunscreen doesn't block all UV rays, so even if you've applied adequate SPF, you'll still get some benefit from being outside, says Giovannucci. But his recommendation is to talk to your doctor about taking a vitamin D supplement—1,000 IU/day is enough for most people to avoid becoming deficient.