Read the fine print: Calcium supplement studies

Two studies — one in the Lancet, one in the British Medical Journal — have reported that calcium and vitamin D supplements don't prevent fractures. This sounds like another health news about-face: These supplements have long been touted as a good way to keep bones strong, and many previous studies have shown just the opposite — that they do help prevent fractures. So how could two large studies, published in important medical journals, reach the opposite conclusion?

This is really a lesson in careful reading. The headlines got the broad brushstroke right: Both studies did find that after about two years, people randomly assigned to take calcium and vitamin D had just as many fractures as those who took placebo pills.

But in the Lancet study, most of the 5,292 subjects were women, all were age 70 or over, most lived in the community (as opposed to a nursing home), all were mentally sound, and all had already had a broken bone. In the British Medical Journal study, all 3,314 subjects were women, all were 70 or over, and all had at least one of the following risk factors for fracture: weight less than 128 pounds, a smoking habit, a family history of hip fracture, and overall poor health.

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