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Calcium supplements and heart risk: New fears

Consumer Reports News: April 20, 2011 01:08 PM

New evidence adds to concerns that taking calcium supplements to protect your bones may cause problems for your heart. The latest study of calcium supplements says calcium is likely to cause more heart attacks or strokes than it prevents fractures.

We first reported on this last July, when researchers reviewed all the evidence from randomized controlled trials comparing calcium supplements (of any type, at any dose) with a pretend drug (a placebo). They found an increased risk of heart attack for people taking calcium.

Last year’s review was criticized for not including people taking vitamin D as well as calcium. A big study (called the Women’s Health Initiative, or WHI) had found no increased risk for women randomly allocated to this combination of supplements, which seemed to undermine the case against calcium.

So the researchers went back and took a closer look at the WHI study. They noticed something unusual - half the women in the study were already taking calcium or vitamin D supplements before the study began, and they were allowed to carry on taking them. The effects of the supplements, whether positive or negative, were likely to be diluted, because many women randomly allocated to the placebo were actually taking calcium and vitamin D.

The researchers decided to analyze the WHI data again, but this time look separately at the women who were not taking calcium supplements by choice.

This time they found an increase in heart attack risk in line with their previous study - around 25 percent to 30 percent. Also, when the researchers added that data - along with two more recent studies - to their original review, the overall findings were strengthened. The figures now show that taking calcium supplements, with or without vitamin D, raises the risk of heart attacks and strokes.

So does the risk outweigh the benefit of stronger bones? According to figures in the study, if 1,000 people take calcium supplements (with or without vitamin D) for five years, six will have a heart attack or stroke as a result of treatment, but only three people will avoid having a fracture. So for many people, the answer is likely to be no.

However, it’s important to keep in mind that the increased risk is not large. If your personal risk of having a fracture is bigger than your risk of having heart problems, calcium still may be a suitable treatment. But you may want to up the calcium in your diet first. That’s because, while calcium supplements seem to raise heart attack risk, eating a diet rich in calcium does not. The researchers say this may be because supplements quickly raise the level of calcium in the blood stream. Calcium in food is likely to be absorbed more slowly.

Bottom line.
Taking calcium, with or without vitamin D, does seem to modestly increase your risk of a heart attack, and possibly a stroke. Eating more calcium in your diet doesn’t seem to cause these problems. If you are taking calcium, you may wish to discuss this with your doctor. To look at the full range of treatments for weak bones, see our information on osteoporosis.

Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women’s Health Initiative limited access dataset and meta-analysis
. [BMJ]

Anna Sayburn, BMJ Group has partnered with The BMJ Group to monitor the latest medical research and assess the evidence to help you decide which news you should use.

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