Calculating the risks of taking calcium

If you're one of the millions of older Americans who take calcium supplements, you might have been startled by this recent headline (or a variation of it): "Calcium supplements linked to increased risk of heart attacks."

Pretty worrying stuff, although the increase in risk noted in the study was actually quite small. Nonetheless, these findings raise an important question: do the benefits of taking calcium supplements outweigh the risks for most people?

You might expect the answer to be yes, considering that many older people don't get enough calcium from their diet, and this can increase their risk of thin and weak bones that break easily ( osteoporosis). Women are especially vulnerable to brittle bones as they get older.

However, studies have raised doubt about whether calcium supplements actually do much to prevent fractures. Although research shows these supplements can modestly increase bone density, this doesn't significantly reduce the risk of broken bones. Throw in the added risk of heart problems, and the answer is less clear.

And this is where the new study comes in.

To learn more about these possible risks, researchers took a close look at 11 good-quality studies comparing calcium supplements with an inactive ( placebo) treatment in nearly 12,000 healthy older adults. Although these studies were designed primarily to assess the potential benefits of calcium supplements, they also gathered data on possible harms, including the frequency of heart attacks, strokes, and other cardiovascular problems.

By pooling this information, the researchers found that people taking calcium supplements were about 30 percent more likely to have a heart attack than those taking a placebo. People taking calcium also had a higher risk of having a stroke and of dying during the studies, although these differences were small enough that they could have been due to chance. Most of the studies lasted around four years, and the participants' average age was 72.

Thirty 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 of those taking calcium had a heart attack during the studies, compared with 130 taking a placebo.

Still, this may be too great a risk increase if people aren't getting much benefit from taking these supplements. To put this in perspective, the researchers calculated that if 1,000 people were treated with calcium for five years, this would prevent only 26 fractures. However, it would cause an additional 14 heart attacks, 10 strokes, and 13 deaths.

These are striking figures that no doubt will prompt more debate and research on the benefits and risks of calcium supplements. 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.

What you need to know. 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 the benefits and risks of these supplements with your doctor. You might mention this research as part of your discussion.

As an alternative, you might try boosting your calcium levels by making changes to your diet. For example, you might add in more dairy products, green leafy vegetables, and fish with edible bones, such as sardines. Calcium from foods, say the researchers, does not appear to increase the risk of heart and circulation problems.

—Sophie Ramsey, patient editor, BMJ Group

ConsumerReportsHealth.org 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.

If you're concerned about the risks associated with your supplements, read our new report on dangerous supplement ingredients and find out if calcium is a supplement you should consider.

—Aaron Bailey