Vitamin D has been the subject of great debate in recent years, with most experts agreeing that we’re dangerously deficient but little consensus regarding just how much we need—or how we should be getting it. According to the most recent National Health and Nutrition Examination Survey, nearly half of all U.S. adults are vitamin D deficient, and even more have levels that are lower than is ideal.
We need D. Studies have shown that vitamin D—which is, in fact, not a vitamin but rather a hormone—may help prevent a number of serious illnesses, including multiple sclerosis, certain types of cancer, and cardiovascular disease. What’s more, it’s believed to be an important factor in ensuring healthy bones, since D aids in the body’s absorption of calcium. But in recent years, deficiencies have climbed in direct relation to our awareness of the need to wear sunscreen. Our bodies produce all the D we need through the sun’s UVB rays most—though not all—of which a decent sunscreen filters out. And though certain foods are rich in D—including fatty fish, eggs, and fortified dairy—most experts have thought that we don’t eat enough of these foods on a consistent basis to take in all the D we need. And so until recently, the smartest move, experts have said, was to get a little D from the sun and the rest from supplements. (The most recent recommendation by the Institute of Medicine put the amount of D we need per day at 600 i.u. for those ages 1 to 70, and 800 i.u. for those over 70, up from the previous recommendation of 200 to 600 i.u.)