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Higher MI rates found with calcium supplements
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Despite their benefits to bone in healthy postmenopausal women, calcium supplements are linked to higher rates of myocardial infarction, stroke and sudden death.
Researchers from the University of Auckland in New Zealand randomly assigned 1,471 healthy postmenopausal women to receive 1 g of elemental calcium supplementation (n=732) or placebo (n=739) over a five-year period to determine the connection between calcium supplements and cardiovascular events. The mean age of participants was 74 years.
MI was more common in the calcium group than in the placebo group (45 events in 31 women vs. 19 events in 14, P=.01), as was the composite endpoint of MI, stroke or sudden death (101 events in 69 women vs. 54 in 42, P=.008).
Despite the number of events reported, the researchers found that 44 women need to be treated for five years to cause one MI. Also over five years, 56 women need to be treated to cause one stroke, and 29 need to be treated to cause one cardiovascular event. In comparison, 50 women need to be treated to prevent one symptomatic fracture. – by Stacey L. Adams
BMJ. 2008;336:262-266.
I am a little surprised at the data. That's not to say it isn't correct, but I am surprised. According to the study, patients had a very good dietary calcium intake at baseline. Dietary calcium intake was approximately 850 mg/day on average. The researchers may be overloading the patients with calcium, but while I don't know that for sure, 850 mg/day is a pretty good amount of dietary calcium. There is evidence that low bone density itself is a risk factor for coronary artery disease. One wonders whether this population of women aged 74 who had not been on any calcium supplement, any vitamin D supplement or any medication for osteoporosis might have had osteoporosis before the start of the study, which may have contributed to coronary artery disease.
I had the good fortune of being a coauthor on a paper by Dr. Pam Marcovitz in The American Journal of Cardiology back in 2005 and it showed that bone density is a very good predictor of coronary artery disease. There are a number of other papers linking low bone density to heart disease. This population could have had low bone density and been at increased risk for heart disease on the basis of that alone, but one cannot be sure. It is not included in the discussion of the manuscript and none of the listed citations include this topic. Nonetheless, the data are very important and we need to be aware of this information, but it is critical to know whether or not this information is true in the low bone density population or regular bone density population. As a society, we need to be extremely careful as we use supplements. Everybody should not be getting the same thing, which is a very hard message to get across. Too much of a good thing is not good for anyone.
– Michael Kleerekoper, MD