Of all dietary supplements, calcium has probably been the least controversial. Even doctors who are generally unenthusiastic about supplements are likely to advise many patients to take calcium to help protect their bones. In fact, calcium was the first supplement the Wellness Letter ever recommended, way back in the 1980s—at least for readers who didn’t get enough calcium from food.
As a possible bonus, studies in recent years have linked higher intakes of calcium with a lower risk of heart disease and colon cancer.
No wonder, then, that there was shock and confusion a few months ago when a new analysis concluded that calcium pills actually increase the risk of heart attacks. Published in BMJ (formerly called the British Medical Journal), it selected 11 placebo-controlled studies, involving nearly 12,000 women, and pooled the data from them.
It found that women taking calcium (averaging about 1,000 milligrams a day) had a 27 percent increased risk of a heart attack. That translated into 36 extra heart attacks over the course of two to five years.
Calculating calcium’s real effect
Many expert groups—including the National Osteoporosis Foundation, American Society for Bone and Mineral Research and Osteoporosis Australia—quickly pointed out faults in the new analysis and reiterated their calcium guidelines. Here are a few concerns raised about the BMJ analysis:
- It included only 11 of the hundreds of published studies using calcium supplements. Of those 11, it seems that only one found significantly increased coronary risk, and that lone study was done by the same research group that did the new paper. One strength of such analyses (called meta-analyses) is that they set strict criteria about which studies to include, but that lays them open to the charge of cherry-picking the data—a charge that has been made against the new paper.
- Because all the studies were designed to look at the effect of calcium on bone health, not heart disease, half of them did not have complete data on cardiovascular events, and a lot of the data were unpublished or self-reported, so their accuracy has been called into question.
- Oddly enough, despite the higher rate of heart attacks, the analysis found no increase in deaths among the calcium takers. The accompanying editorial thus said it’s possible that the seemingly higher risk “is not a true effect.”
- Most important, the analysis excluded the many studies that gave subjects even small amounts of vitamin D supplements along with the calcium, which is the preferred regimen for bone health. One of these was a large, well-known study from the Women’s Health Initiative, which found that calcium plus vitamin D did not affect the risk of heart attacks. Besides being essential for the absorption of calcium, vitamin D may help reduce the risk of heart disease.
According to the noted calcium expert Robert Heaney, M.D., of Creighton University in Omaha, “the BMJ article is a terrible one, and I am not sure why it has evoked as much publicity as it has—it doesn’t repeal all of the prior studies.”
Had studies that also used vitamin D been included, he noted, the adverse effect would have gone away—“if anything, the results would tip in the direction of benefit rather than risk.” In a large study that he and his colleagues conducted, Dr. Heaney found that women taking calcium supplements had a reduced risk of heart attacks.
Our advice: This study has many serious limitations, but it does raise concerns that require further research. Keep in mind, however, the benefits of an adequate calcium intake for bone health are well established. Thus, we continue to advise women over 50 and men over 65 to aim for 1,200 milligrams of calcium a day from food and/or supplements. Younger people should get at least 800 to 1,000 milligrams a day.
It’s best to get as much as you can from your diet, since calcium-rich foods are also packed with other key nutrients for bone health, as well as heart health. Just as important, unless you know from a blood test that your vitamin D level is adequate, take 800 to 1,000 IU of vitamin D a day, especially if you are in an older age group, have dark skin, and/or get little sun exposure. It’s very hard to get that much D from food.