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Are calcium supplements harmful for the heart?

Evidence is mounting that the benefits of taking calcium supplements may not outweigh the risks, with another study linking these supplements to a raised risk of heart attacks.

BMJ Group News

What do we know already?

calcium tablets

Many older people don't get enough calcium from their diet, which may increase 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. Doctors often recommend taking calcium supplements to make up for this gap.

But research has cast doubt on whether the benefits of these supplements outweigh the risks. Although studies show that taking calcium can modestly increase bone strength, this doesn't always reduce the risk of fractures by much. Some studies have also suggested that calcium supplements may raise the risk of heart attacks and strokes. This is somewhat surprising, given that other studies have also found that calcium supplements may help lower high cholesterol and high blood pressure - both risk factors for heart disease.

So are calcium supplements helpful or harmful when it comes to our hearts? To explore this, researchers gathered data on nearly 24,000 adults, aged 35 to 64, from a large study in Germany. Participants filled in questionnaires about their usual diet, whether they took any supplements, and their health and lifestyle. Researchers then recorded, over an average of 11 years, whether people who had more calcium in their diet - from foods and supplements - were more likely to have a heart attack or stroke, or die of heart disease.

What does the new study say?

People who took calcium, with or without other supplements, had a higher risk of having a heart attack compared with people who didn't take any type of supplement. The risk was highest for those who took calcium supplements alone, with nearly 3 in 100 people having a heart attack during the study, compared with between 1 and 2 in 100 people not taking any supplements.

After accounting for things that can affect people's risk of a heart attack, such as their age and whether they smoke, the researchers found that people taking calcium were more than twice as likely to have a heart attack.

Interestingly, when the researchers looked at the calcium people got from foods, they found that those who had moderate amounts of calcium in their diet (820 milligrams daily, on average) had a slightly lower risk of having a heart attack than those who had the lowest levels. But people who had the most calcium (1,100 milligrams daily, on average) didn't have a lower risk.

The researchers found no link between calcium and the risk of stroke or of dying from heart disease.

How reliable is the research?

This was a large and well-conducted study. But it has a couple of weaknesses.

Asking people to fill in questionnaires isn't the most reliable way to gather information on people's diets, as they may not accurately recall what they ate and how much. Also, the participants filled in these questionnaires only at the start of the study. This means that the researchers weren't able to account for any changes in diet and lifestyle during the 11 years of follow-up. This could have affected their findings.

Finally, it's important to note that this type of study can't show cause and effect, so we can't be certain that taking calcium supplements was what increased people's risk of a heart attack. However, it is notable that this study echoes findings from previous research. This adds weight to its conclusions.

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