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Calcium: Heart Risk for Older Women?

Study Shows Calcium Supplements May Up Heart Attack Risk in Postmenopausal Women
WebMD Health News
Reviewed by Louise Chang, MD

Jan.15 2008 -- Calcium supplements, generally thought to preserve both bone and heart health, may boost the risk of heart disease in healthy postmenopausal women, according to New Zealand researchers.

"Loading with high doses of calcium reduces bone loss but at a cost in heart health that is not justified," says researcher Ian Reid, MD, professor of medicine and endocrinology at the University of Auckland.

But a U.S. expert on calcium supplementation says the findings may be a fluke and at this time don't warrant any change in the recommendation to get sufficient calcium through diet and supplements.

Calcium, Heart Attack Study Details

Reid and his colleagues followed 1,471 healthy postmenopausal women, ages 55 and above, assigning half to get a daily calcium supplement of 1,000 milligrams and half to placebo pills. The average age in both groups was 74.

Calcium supplements are typically prescribed to women after menopause to preserve bone health, and some studies suggest it might also protect heart health by improving the ratio of good cholesterol to bad cholesterol.

The New Zealand researchers initially conducted the study to look at the effect of calcium on bone health, says Reid, who has received research support from calcium supplement manufacturers. This study is what is known as a secondary analysis. Researchers evaluated the women's calcium intake from diet and examined them every six months for five years, looking for reports of heart attack, stroke, or sudden death.

The women in the supplement group got 861 milligrams of calcium from diet per day, on average, boosting their total daily intake to 1,861. The placebo group averaged about 853 milligrams of calcium daily from their diet.

(Has your doctor talked to you about heart risks? Talk with others on WebMD's Bone Health and Osteoporosis message board.)

Calcium, Heart Attack Results

To obtain a more complete picture, the researchers also looked for events not reported at the visits by checking hospital admissions and reviewing death certificates of those who had died.

Heart attacks were more common in the calcium group, with 31 women on supplements having 36 heart attacks compared to 21 women on placebo having 22 heart attacks during the follow-up period.

The risk of a heart attack was about 1.5 times greater for those in the supplement group, but the link did not reach statistical significance.

Considered together, strokes, heart attack, or sudden death were more common in those on supplements than on placebo, but the differences -- when taken as a whole -- were statistically only of borderline significance, Reid's team found.

The researchers took into account such factors as cigarette smoking, high cholesterol, and blood pressure problems.

Calcium, Heart Attack: What's the Mechanism?

Reid cautions that the findings must be replicated and plans to do more research on the proposed link.

But he speculates that the calcium supplements may elevate blood calcium levels and possibly speed calcification in blood vessels, which is known to predict the rates of vascular problems such as heart attack.

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