Many older people, especially women, take calcium supplements to help keep their bones strong. But a new review of studies suggests these supplements may also slightly increase their risk of having a heart attack. This raises questions about whether the benefits of taking calcium supplements outweigh the risks for many people.

What do we know already?

Calcium is an essential nutrient for building strong bones and keeping them healthy. Your body gets this mineral from the food you eat. For example, there's lots of calcium in dairy products, green leafy vegetables, and fish with edible bones, such as sardines.

However, many older people don't get enough calcium from their diet. This increases their risk of osteoporosis, a condition marked by thin and weak bones that break easily. Women are especially vulnerable to this as they get older. Many older people take calcium supplements to help prevent or treat this bone disease.

However, some research has cast doubt on the value of these supplements. Although studies show that taking calcium can modestly increase bone strength, this doesn't reduce the risk of fractures by much. Studies have also suggested that calcium supplements may raise the risk of serious heart and circulation problems, such as heart attacks and strokes. Previously, this was thought to mainly affect people with kidney failure. But a recent study also found a higher risk of heart attacks among healthy older women taking calcium supplements.

To learn more about these possible risks, researchers have now looked at 11 good-quality studies comparing calcium supplements with an inactive (placebo) treatment in older adults. The researchers did a meta-analysis, which means they pooled the results of the studies to see what conclusions they could draw from this larger body of research.

What does the new study say?

People taking calcium supplements were about 30 percent more likely to have a heart attack during the studies than those taking a placebo. They also had a higher risk of having a stroke and of dying, although these differences were small enough that they could have been down to chance.

The risk of heart attacks tended to be greatest among those taking higher doses of calcium (more than around 800 mg a day). But it didn't vary much by people's age, sex, and the type of supplement they took. On average, the studies followed people for about three and a half years. The participants' average age was 72 and they were all considered healthy, although some had osteoporosis.

The researchers point out that 30 percent isn't a huge increase in heart attack risk, considering that people's risk was low to begin with. Among the nearly 12,000 participants, only 166 taking calcium had a heart attack during the studies, compared with 130 taking a placebo. Even so, this may be too high a risk if people aren't getting much benefit from taking these supplements.

How reliable are the findings?

These findings should be fairly reliable. The review included only double-blind randomised controlled trials, which are the best type of study for finding out the effects of a treatment.

However, it's important to note that the review didn't look at taking calcium combined with vitamin D, which is a popular type of supplement. So we can't say whether these combined supplements might also be linked to a higher risk of heart attacks.

Where does the study come from?

This review was conducted by researchers with universities in the UK, US, and New Zealand. It was funded by the Health Research Council of New Zealand and the University of Auckland School of Medicine Foundation. The research was published in the BMJ (British Medical Journal), which is owned by the British Medical Association.

What does this mean for me?

If you are an older adult and take calcium supplements, this research suggests you may have a slightly higher risk of having a heart attack. This is something to consider when weighing up the benefits and risks of taking these supplements. As an alternative, you might try boosting your calcium levels by making changes to your diet. Calcium from food doesn't appear to increase the risk of heart and circulation problems, say the researchers.

If you have osteoporosis or are at risk of developing this disease, other treatments work better than calcium to improve your bone strength and reduce your risk of fractures. These include bisphosphonate drugs, such as alendronate (brand name Fosamax). Your doctor may recommend taking calcium along with these drugs, although more research is needed to explore the pros and cons of this treatment approach.

What should I do now?

If you take calcium, you may wish to talk to your doctor or pharmacist about whether the benefits of these supplements outweigh the risks for you. You might mention this research as part of your discussion.

From:

Bolland MJ, Avenell A, Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010; 341: c3691.

To learn more, see our information on osteoporosis.

© BMJ Publishing Group Limited ("BMJ Group") 2010