Every day, millions of Americans swallow calcium pills in an attempt to keep their bones strong. For decades, women in particular have been told that extra calcium is critical to ward off osteoporosis.
Despite the dogma, there is less evidence to support this advice than most people realize. More than 100 studies have considered whether sources of calcium, including milk, dairy foods and supplements, actually prevent fractures. The majority show no benefit.
More startling, however, is the question raised last summer about the potential for calcium supplementation to increase the risk of heart attacks (BMJ, Aug. 7, 2010). The researchers analyzed 11 trials that included approximately 12,000 participants. They found that those randomly assigned to take calcium supplements were about 30 percent more likely to suffer a heart attack than those on placebo. As the investigators note, this is a relatively modest increase in risk, but so many people take calcium supplements that the overall damage might be significant.
Not surprisingly, this analysis created controversy in the medical community and confusion for the public. Readers of this column have expressed their concern:
"Thank you for writing about calcium supplements. I have been taking a 1,000 mg calcium supplement daily for years. About a year ago, I had what my doctor called a mild heart attack. I failed a stress test, which led to a cath procedure. That was clear, but I remember the doctor saying it could possibly be from calcification rupturing or in some way blocking the microvessels around my heart.
"He was baffled, and so am I, because the month before I'd had a health screening that indicated I was at very, very low risk of heart attack. I have low blood pressure and excellent total cholesterol, LDL and HDL numbers. I am slim, I eat right, and I exercise."
There is no way to tell whether this reader's heart problem was caused by the calcium supplements. The authors of the BMJ report hypothesized that excess calcium might lead to calcification in blood vessels. This possible explanation has added to readers' confusion:
"I have always worried about calcifications associated with calcium supplementation and been told firmly and consistently that NO, there is absolutely no relation. I am alarmed by the report of a connection between calcium and heart attacks. I've heard that if these supplements also contain vitamin D and magnesium, they are safer."
The analysis that caused such consternation did not include studies of calcium supplements with vitamin D. A different systematic review concluded that adding vitamin D might help protect the heart (Annals of Internal Medicine, March 2, 2010).
There is now so much uncertainty about the benefits and risks of calcium supplementation that it is no wonder people are dazed. Anyone who would like more information about building strong bones and preventing fractures may find our Guide to Osteoporosis helpful. To request a copy, please send $3 in check or money order with a long (No. 10), stamped (61 cents), self-addressed envelope to: Graedons' People's Pharmacy, No. U-92, P.O. Box 52027, Durham, NC 27717-2027. It also can be downloaded for $2 from our website: www.peoplespharmacy.com.