Calcium might be tied to heart attack risk, but evidence still weak

Calcium supplements appear to slightly raise the risk of heart attack, a new analysis suggests. But the data, from postmenopausal women who took supplements over seven years, are far from conclusive.

So don’t throw out the multivitamins just yet – or those calcium supplements that many women take for bone health. Not all doctors are convinced that this study, led by the University of Auckland, is the last word on calcium supplements. Or that it changes the debate at all.

The results from previous studies of calcium and heart attack risk, including ones from the same research team, have been widely criticized. In controlled studies, some participants are supposed to take one substance while other participants take a different one, often a placebo. But in this large calcium trial, many women from both groups took extra personal calcium supplements on the side.

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This new study says it took women’s calcium-popping into consideration. Researchers from the University of Auckland analyzed data from eight studies plus a data set from the Women’s Health Initiative, a 7-year study of 36,282 postmenapausal women who were randomly selected to take calcium and vitamin D or a placebo. The team limited the data to the 16,718 women who were not sneaking extra calcium, measuring four heart events: heart attack, coronary revascularization (a type of heart surgery), death from coronary heart disease, and stroke.

The researchers found a 24% increase in the risk of heart attack and a 15% increase in the risk of a heart attack or stroke from taking calcium, with or without vitamin D, they reported Tuesday in the British Medical Journal.

The authors conclude that a second (or third) look at how calcium is used to treat osteoporosis is warranted. But an accompanying editorial argues that, yet again, the study design is flawed, and it’s still because of the women who swallowed extra pills to make sure they got enough calcium. Two researchers write:

“Unfortunately, although it is straightforward to remove those who were taking their own supplements from the cohort when they make up uneven parts of the randomised arms, interpreting the results is difficult because of the loss of equal randomization.”

By excluding women who were taking personal supplements, the authors no longer had two randomized groups to compare. That might be one reason for contradictory results in the data—how women who did not use personal supplements were at 16% increased risk for heart attack or stroke, but women who did use personal supplements had a 16% less risk of death.

So the modest increase of heart attack risk may be even smaller.

Dr. Bart Clarke, an endocrinologist at the Mayo Clinic in Rochester, Minn., says the study adds to the growing concern over calcium, but isn’t a reason to panic:

“The study is not conclusive proof, and there are limitations to the study pointed out in the article, but the implication is that calcium supplements may increase the risk of heart attack over time,” Clarke wrote in an email.


Obviously more study is needed, but that inconclusiveness leaves women wondering how to take just enough calcium supplements for healthy bones without worrying they’re increasing their risk for heart attack.

Clarke suggests women look for food sources of calcium, such as dairy products and greens.

“Calcium intake through the diet did not apparently add to the risk, so it may be safer to take calcium through the diet,” says Clarke.