Mark Pine

As women age, their bones often lose calcium and fractures occur more frequently, a condition called osteoporosis. So it seems logical for older women (and men with osteoporosis) to take calcium supplements. Logical … but perhaps not a good idea.

The BMJ (British Medical Journal) published yesterday a meta-analysis (analysis of combined data) of five clinical trials involving 8,000 people who took calcium supplements or placebo pills. The researchers from universities in New Zealand, Scotland and the United States compared the rates of heart attacks among the participants, who were followed for an average of about four years. Those taking the calcium had a 31% higher rate of heart attacks than those taking the placebo.

The researchers also presented a larger analysis involving eleven clinical trials with 12,000 people. Although these trials provided less detailed information about the participants than first five, the results were similar. Those taking calcium had a 27% higher rate of heart attacks. One important caveat: All the trials compared calcium alone to placebo. Calcium is often taken along with vitamin D, and the results may or may not be applicable to the combination.

Cardiologists from two universities in the U.K. reviewed the implications of the meta-analysis in an accompanying editorial. They noted that no increase in mortality rate accompanied the increase in the rate of heart attacks, raising the possibility of a spurious finding, since an increase in heart attacks should result in an increase in mortality. But they also pointed out that although calcium supplements improve bone mineral density, they have not been found to reduce bone fractures. In view of the possibility that they may contribute to heart disease, it would seem wiser not to take them.

The BMJ also published last January a meta-analysis of clinical trials of supplements of vitamin D with or without calcium. Pooling seven clinical trials involving 70,000 participants, Danish medical researchers found that the combination of Vitamin D and calcium reduced the overall rate of bone fractures by 8% and the rate of hip fractures by 16%. Among the patients who took at least 10 mcg of vitamin D with calcium, the rate of hip fracture fell by 26%. Taking vitamin D alone, however, had no effect on fractures.

The reduction in the rate of hip fractures from taking 10 mcg vitamin D plus calcium is substantial, particularly since hip fractures result in considerable disability and increase mortality. Still, the outcome of a benefit-risk analysis that balances the potential benefit of reducing hip fractures against the potential harm of increasing heart attacks is not clear. Although the meta-analysis published by the BMJ yesterday did not investigate heart attacks in people taking calcium along with vitamin D, the possibility that the same increase would also occur with the combination is cause for concern.

The authors of the editorial take the view that calcium supplements “seem to be unnecessary in adults with an adequate diet. Given the uncertain benefits of calcium supplements, any level of risk is unwarranted.” For the time being, the better course would seem to be eating well, including adequate amounts of food containing calcium, but not taking more of the mineral in supplements.