Recent studies have examined vitamin D's bone-boosting potential and reached confounding conclusions: One, in the July 25 Archives of Internal Medicine, showed little difference in bone loss between post-menopausal black women who took both 800 International Units, or IUs, of vitamin D plus calcium supplements for three years and those who took just calcium. Yet a study by Boston University researchers showed Americans are getting too little vitamin D to ward off osteoporosis and other diseases. Studies in the April 30 BMJ (formerly the British Medical Journal) and the May 7 issue of The Lancet argued that vitamin D supplement intake had little impact on the incidence of fractures in older people. But a review of published research regarding vitamin D supplementation and fracture prevention in older people in the May 11 Journal of the American Medical Association found that high doses (700 to 800 IUs per day) of vitamin D appear to reduce risk of fracture but lower doses (400 IUs) did not. Confused? We thought so.

The Hard Facts Bess Dawson-Hughes, immediate past president of the National Osteoporosis Foundation (NOF), said the BMJ and Lancet studies can't quite be trusted because so many participants stopped taking their daily pills. The study involving black women is more reliable, she said, but "we need more information on this population" before concluding that vitamin D is not important to African Americans. "That would be a major over-interpretation . . . and would have the potential to do harm."

Hector DeLuca, biochemistry professor at University of Wisconsin, Madison, who has devoted his career to studying vitamin D, says variables including dose, calcium intake, diet and exposure to sunlight make the vitamin's effects difficult to pin down. But because it's "really a very safe substance" at levels below 2,000 IUs a day, he says there should be no debate about taking it.

Bone Up The NOF recommends women over 50 take in 400 to 800 IUs of vitamin D daily, through judicious sun exposure (without sunscreen), foods such as fortified dairy products, egg yolks, liver and saltwater fish, and supplements, including multivitamins.

-- Jennifer Huget