Calcium not as protective as believed

Some researchers said the effect would have been clearer with higher doses of vitamin D, perhaps up to 1,000 units daily. The vitamin helps the body absorb calcium and promotes muscle health, reducing falls.

"We don't want to send the message to people to throw away their calcium pills, which was my wife's first reaction," said Lasser, one of the study authors.

The study did show a significant side effect with the diet supplements: a 17 percent increase in the risk of kidney stones. But several doctors downplayed that risk, saying hip fractures are typically much worse than kidney stones.

Doctors said the study suggests that women at higher risk of fracture -- whose tests show lost bone density -- likely need more than diet supplements. They may require osteoporosis drugs.

The study also checked whether the supplements might help prevent colon cancer, and the results indicated there was no benefit. That wasn't a big surprise partly because past studies had not signaled much benefit.

Still, the researchers plan to check participants in future years, because colorectal cancer can take 10 to 20 years to develop.

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