As they age, people often take in more calcium, either through their diet or with supplements, in an effort to keep their bones strong and to lessen the chances of a fracture. Does this strategy work?

THIS STUDY analyzed data from 72 studies, involving nearly a million people age 50 and older who increased their calcium intake from dietary sources such as milk, from calcium supplements (usually 800 to 1,000 milligrams daily) or from both. Study periods generally lasted five to six years.

More than 75 percent of the studies found no link between dietary calcium consumption and fracture risk, including among participants who took in the most calcium (1,200 mg daily); the remaining studies showed only a weak association between dietary calcium and fractures.

In the studies on calcium supplements, people who took them were about 11 percent less likely to have broken a bone than were those who did not take the supplements, but taking calcium supplements had no effect on hip or forearm breaks. The researchers attributed most of the risk reduction from supplements to one large study of frail elderly women with vitamin D deficiency, which they suggested may have skewed the results.

The highest-quality studies showed no link between calcium supplements and fracture risk.

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WHO MAY BE AFFECTED? People 50 and older. About half of all older women and a fourth of older men will break a bone because of osteoporosis, a thinning and weakening of the bones that can develop at any age but occurs most often in older people.

A lifetime of getting sufficient calcium and vitamin D, which helps with calcium absorption, along with healthy habits such as exercising and not smoking, are considered good ways to prevent osteoporosis. Dietary sources of calcium include dairy products, leafy green vegetables, certain fish and calcium-fortified foods. Current guidelines recommend that people older than 50 consume 1,200 mg of calcium every day. Some people experience side effects from calcium supplements, such as kidney stones and gastrointestinal problems.

CAVEATS Among the supplement studies, dosage differed from study to study. The quality of the studies varied, with the researchers noting that small- and moderate-size studies on calcium supplements were of lower quality.

FIND THIS STUDY Sept. 29 online issue of the BMJ (www.bmj.com/theBMJ).

LEARN MORE ABOUT calcium at ods.od.nih.gov (click on “Dietary Supplement Fact Sheets”) and www.mayoclinic.org (search for “calcium”).

The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment's effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician.