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How Much Is Enough?
An 8-ounce glass of milk or fortified orange juice has about 100 international units (IU) of vitamin D and a typical multivitamin has 200 to 400 IU. Other good dietary sources of vitamin D include cod liver oil, which has 1360 IU of vitamin D per tablespoon; salmon, which has 425 IU per 3-ounce serving; and herring and sardines. The recommended intake of adequate amounts of vitamin D depends on a person's age. The Food and Nutrition Board (FNB) of the Institute of Medicine says that older women should consume 400 to 600 IU per day in order to have adequate vitamin D intakes.
Like Holick, Saag says he believes vitamin D deficiency is an under-recognized health problem in the U.S. today.
"General population studies indicate that about one in three people are vitamin D deficient," he says. "This is a particular problem during the winter months, when sun exposure is minimal. This is another reason why people should think about supplementing their diets with a multivitamin."
But Holick says most people need to take 1000 IU of vitamin D each day. And he says even this amount may be inadequate in people who have no exposure to the sun.
"Most people get between 90% and 95% of their vitamin D from sun exposure, so if you eliminate that you are setting the entire country up for vitamin D deficiency," he says.
The director of the Vitamin D Research Lab at Boston University, Holick advocates a limited amount of sun exposure, without sunscreen, every day -- a message that the nation's top dermatology group abhors. In a recent press release, officials with the American Academy of Dermatology expressed "deep concern" that the public is being misled "about the very real danger of [unexposed] sun exposure -- the leading cause of skin cancer."
But Holick counters that it does not take much sun to get more than enough vitamin D -- only a few minutes of unprotected sun exposure at most for most people.