Vitamin D is so critical to our health that nature designed a fail-safe way to obtain it: from the sun. Throughout history, exposure to the sun gave humans the vital doses needed to build bones, protecting children against the characteristic bowed legs of rickets and adults from osteomalacia, or softening of the bones.
Certainly, some of our vitamin D is provided by foods—fatty fish and egg yolks, for example. But until 1931, when milk began to be fortified with this fat-soluble vitamin, the sun was our main source, its ultraviolet B rays penetrating the skin’s uppermost layer, causing skin cells to produce a vitamin D precursor. (The precursor, along with vitamin D from food, is processed by the liver and kidneys and converted to D3—the active form of the vitamin.)
Now, we spend more time indoors, in cars or behind computers. We drink less milk and when we do go out, slather on sunscreen. It is no coincidence, experts say, that rickets (which had been virtually wiped out until the 1990s) is making a comeback. Scattered cases of rickets in African-American infants and breast-fed babies have been documented as far south as Georgia; just last February, researchers at the University of Pittsburgh found that over 80 percent of pregnant black women and nearly half of pregnant white women (and the babies they later gave birth to) were classified as “insufficient” or “deficient” in vitamin D. Older people in hospitals and nursing homes are especially likely to lack the vitamin; in one study, 57 percent of elderly patients admitted to a Boston hospital were found to be vitamin D-deficient, according to blood samples and diet records. What’s more, dietary surveys suggest that most Americans, young and old, aren’t getting recommended amounts of the vitamin.
Ironically, these deficiencies have been coming to light at the same time research is uncovering promising new roles for vitamin D—much of it suggesting that higher (often much higher) daily doses of the vitamin are needed for optimal health. Researchers have long been urging policy makers to rethink current dietary recommendations, and in recent months their voices have been getting louder. Here, some light on the debate about vitamin D—and what you can do now to stay healthy.