(HealthDay News) -- Even a short period of calcium and vitamin D supplementation can greatly reduce the risk of stress fractures (overuse injuries to the bone) in women, a U.S. study finds.

The study included more than 5,200 female U.S. Navy recruits, ages 17 to 35, doing eight weeks of basic training. They were divided into two groups -- one group received daily pill supplements of 2,000 mg of calcium and 800 IU of vitamin D, while the other group received placebo pills.

Vitamin D helps the body absorb calcium, which is vital to bone formation and repair.

During the study, 170 of the recruits in the placebo group suffered stress fractures, 25 percent more than the group taking the supplements. The researchers also noted that a history of exercise decreased risk among women in the study, while cigarette smoking increased the risk.

"What really surprised us is that calcium/vitamin D supplements made a significant difference in such a short period of time. Frankly, we were not sure we would see any statistically significant results in only eight weeks," principal investigator Joan Lappe, a professor of nursing and medicine at Creighton University in Omaha, Neb., said in a prepared statement.

She said these findings in military recruits may also apply to high-school track and field athletes, who are at increased risk for stress fractures.

"It appears that supplementation with calcium and vitamin D provides a health-promoting, easy and inexpensive intervention that does not interfere with training goals," Lappe said.

The study was presented this week in San Diego at the annual meeting of the Orthopaedic Research Society.

More information

The American Academy of Orthopaedic Surgeons has more about calcium.

By Robert Preidt
SOURCES: Creighton University, news release, Feb. 11, 2007
Last Updated: January 2008
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