Although scientists continue to debate among themselves how much vitamin D is enough, they agree that deficiency is widespread and that current federal guidelines are woefully inadequate.
The guidelines, last updated in 1997, call for 400 IU (international units) a day for adults ages 51 to 70 and 600 IU a day after age 70. New recommendations will be released in a few months, but several professional groups and vitamin D researchers have already called for far higher levels.
Creighton University's Robert P. Heaney, M.D., a vitamin D researcher, encourages people over age 50 to take a daily supplement of between 1,000 and 2,000 IU, "in addition to the vitamin D they're getting from sun exposure, milk and multivitamins." As far as the likelihood of getting too much vitamin D from supplements, according to Heaney, you'd have to consume more than 30,000 IU a day for many months before you would need to be concerned about health problems from too much D. And there is no way to get too much vitamin D from the sun, because the skin breaks down any excess.
The International Osteoporosis Foundation advises an across-the-board daily supplement of 800 to 1,000 IU for men and women over age 60 who are not getting substantial, regular sun exposure — "and that's practically everyone," says Tufts University's Bess Dawson-Hughes, M.D.
Odds are you'll need at least 2,000 IU a day to achieve adequate blood levels if you're overweight or obese, rarely get outside, routinely use sunscreen and cover up when you're in the sun, fall a lot, or have dark skin or osteoporosis.
Some experts recommend a vitamin D blood test only if you fit into this high-risk group. Others recommend that all adults ask their doctor to order the test. Results should show a vitamin D level of at least 30 ng/mL (nanograms per milliliter).
Nissa Simon, a health writer, lives in New Haven, Conn.