How Much is Enough?
For now the U.S. recommendations for adequate intake of vitamin D are 200 international units (IU) per day for adults under age 50, 400 IU for adults aged 50 to 70 and 600 IU for adults over 70.
“How much you need from your diet is inversely proportional to what you make from the sun,” explains Giovannucci. “Lifeguards probably don’t need any from their diet.” But the rest of us need to be more vigilant, unless we take supplements or love drinking milk.
Since many Americans have trouble getting even the recommended doses, the 2005 Dietary Guidelines for Americans—the government’s authoritative voice on what to eat to stay healthy—declared that the elderly, people with darker skin and those exposed to insufficient sunlight (people who are housebound) need 1,000 IU daily—an amount that’s hard to achieve without taking a daily supplement.
What’s more, those recommendations are focused only on keeping rickets and osteomalacia at bay, says Robert Heaney, M.D., a leading vitamin D expert at Creighton University in Omaha, Nebraska: “They don’t in any sense ensure the health of the total body.”