Vitamin D craze: Real hope or mostly hype?

Once this was understood, vitamin D was produced synthetically and foods, mainly milk, were fortified with it. An eight-ounce glass of milk contains about 100 International Units (IUs) of vitamin D.

By comparison, if you are Caucasian and expose 40 percent of your skin to midday summer sun in most of the United States, you will receive a dose of roughly 1,000 IUs per minute. The darker your skin, the less vitamin D you’ll receive from the sun. Anyone living north of about 35 degrees latitude — such as New York, Denver, Madrid (some high elevations excepted) — will receive none of the required wavelengths in midwinter.Unlike most other nutrients, there is no “Recommended Daily Allowance” or RDA, for vitamin D. Instead, the Department of Agriculture uses a measure called “Adequate Intake Value” based on what’s needed to keep bones healthy. The adequate intake value for people up to age 50 has been set at 200 IUs per day, (a typical daily multivitamin pill contains 400 IUs), but most experts now agree that while this may prevent rickets, the amounts should be raised. Last year, for example, the American Academy of Pediatrics doubled its recommendation for children, including infants, to 400 IUs.

Even so, “we do not know where we want vitamin D to be,” said Rebecca Jackson, professor of medicine at Ohio State University and an expert in vitamin D and bone health. “We do not know what is an optimal level of vitamin D for good health.”