Calcium boosts bones.

A new study corroborates the results of the Women's Health Initiative, which led to considerable confusion last February (see cover story, April 2006). Once again, calcium supplements reduced the risk of fractures, but only in women who actually took their pills.

Researchers in Australia randomly assigned 1,460 women over age 70 to take either a placebo or 600 mg of calcium twice a day. After five years, the researchers saw no difference between women assigned to take the placebo or the calcium.

The researchers then looked only at the 830 women (57 percent of the initial participants) who were still taking at least 80 percent of their calcium or placebo pills. Among those women, the risk of fracture was 15 percent in the placebo takers but only 10 percent in the calcium takers.

Calcium didn't raise the risk of kidney stones, as it did in the (much larger) Women's Health Initiative. The only adverse effect: more calcium takers (13 percent) than placebo takers (9 percent) reported constipation.

What to do: Shoot for the recommended 1,200 mg of calcium a day (1,000 mg if you're 50 or younger) to reduce your risk of broken bones. The study suggests that higher doses are better, since the calcium takers were getting 1,200 mg a day from a supplement plus 900 mg of calcium from food and supplements they were taking on their own.

But it's still possible that higher doses of calcium increase the risk of kidney stones. And men should get no more than the recommended levels because other evidence suggests that more than 1,500 mg of calcium a day may raise the risk of fatal prostate cancer.

Arch. Intern. Med. 166: 869, 2006.