Harvard Women's Health Watch

In the journals: Link between calcium supplements and heart attack risk unclear

Older people who take calcium supplements have a 30% increased risk of heart attack, according to a meta-analysis (a review of multiple studies) published online July 29, 2010, in the medical journal BMJ. But another meta-analysis, published by Harvard researchers in Annals of Internal Medicine (March 2, 2010), found that calcium supplements had no effect on cardiovascular events. These conflicting findings have raised questions for clinicians and women, including readers of Harvard Women's Health Watch. Postmenopausal women are generally urged to get adequate calcium through diet and supplements to help protect against osteoporosis and bone fractures. Many now want to know if they should stop taking calcium supplements. The short answer is no, though you should probably get most of your calcium from foods.

The BMJ study

New Zealand researchers analyzed data from 11 randomized trials involving 11,921 participants who were assigned to receive either calcium supplements or a placebo for at least four years. In nine studies, the daily calcium supplement dose was 1,000 milligrams (mg) or more; in the other two, it was 500 mg and 600 mg.

Overall, 2.7% of the women taking calcium supplements had heart attacks, compared with 2.2% of those taking a placebo. The difference was small in absolute terms (163 heart attacks among women taking calcium and 130 among those taking a placebo) but could be medically significant because so many people take calcium supplements.

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