It was just a few years ago that the Institute of Medicine (finally) increased its recommendations on vitamin D intake. The previous guidelines called for a scant 200 international units (IU) to 600 IU daily, depending on age... the current recommendations are 600 IU daily for most Americans and 800 IU for those over age 70. Now a huge recent study suggests that those levels are still too low to keep our bones from breaking as we age.

Researchers pooled data from 11 clinical trials involving a total of 31,022 seniors ages 65 and up, 91% of whom were women. The trials focused on the effects of vitamin D supplements taken with or without calcium. Rather than looking at how much vitamin D participants were given as part of a study, as is typically done, the researchers zeroed in on how much vitamin D people actually did take. Based on that, participants were divided into four groups, or quartiles, ranging from the highest to the lowest levels of actual vitamin D intake.

Findings: In the highest quartile, vitamin D supplementation averaged 800 IU (and ranged from 792 IU to 2,000 IU) per day. People in this quartile were 30% less likely to break a hip and 14% less likely to suffer a nonvertebral fracture, such as in a wrist or forearm, than people in all of the other quartiles. In fact, the results showed no benefit in terms of fracture prevention from taking less than 800 IU daily.

Take-home message: Talk to your doctor about supplementing with at least 800 IU of vitamin D daily. (Note that many multivitamins provide only 400 IU of vitamin D.) But don't fall into a "lots more is lots better" mind-set-excessive vitamin D can lead to high blood levels of calcium, which can cause kidney damage and blood vessel calcification.

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