According to a new study in the October 27th issue of British Medical Journal (BMJ), calcium supplements taken by themselves can increase the risk for myocardial infarction.
It is well known that calcium plus vitamin D supplements taken together prevent bone loss and reduce the risk for fracture in postmenopausal women and are associated with a reduction in the rate of bone mineral density loss at the spine and hip. More importantly, calcium plus vitamin D supplements reduce the overall risk for fracture by 12%. However, calcium by itself has not shown to be nearly as beneficial.
The researchers examined randomized, double-blind, placebo-controlled trials through November 2007 of elemental calcium at dosages of at least 500 mg per day. Researchers did not consider studies that combined supplements of calcium with vitamin D.
The main outcomes of the study were the time to first myocardial infarction, the time to first stroke, and the composite endpoint of myocardial infarction, stroke, or sudden death. The study included data on a total of 20,072 patients. The mean age of participants in these trials was 72 years, and 83% of subjects were women. The mean dose of calcium was slightly more than 1000 mg/day, and both calcium carbonate and calcium citrate were represented in the clinical trials.
Among trials with patient-level analysis, there were 143 and 111 myocardial infarctions among participants receiving calcium supplements and placebo, respectively. Individuals with higher dietary calcium intake appeared to be at a particularly elevated risk for myocardial infarction when taking calcium supplements. Calcium supplementation also appeared to promote a higher risk for recurrent cardiovascular events. There was no significant difference between calcium supplementation and placebo in the risks for stroke, the composite cardiovascular endpoint, or death.
The authors do discuss the major issue with their study. They only analyzed calcium supplementation without vitamin D supplements. Given that calcium supplementation appears most effective in reducing the risk for fracture when combined with vitamin D, the results of this study should not apply directly to most women receiving supplements for bone health. This is particularly salient given that a recent study found that vitamin D supplements at doses of approximately 1000 IU per day were associated with a lower risk for cardiovascular disease (whereas combination therapy with calcium plus vitamin D had no significant effect on the risk for cardiovascular outcomes).
Bonnie - if you are a client and have followed my advice, you should feel at ease because you are not taking supplemental calcium by itself. You are most likely taking a supremely absorbed calcium source along with gut-friendly magnesium and vitamin D3. Well before we started blogging about it (11/15/05, 2/16/06, 1/16/08), I warned that taking supplemental calcium by itself, as well as taking too much, was a bad idea. So the results of this study should not come as a surprise. If you have been supplementing with calcium by itself (especially in the carbonate or citrate form), then you are running the risk of rogue calcification, which can show up in the form of calcium deposits in the arteries.
If you are unsure of how much calcium, magnesium, and vitamin D you should be taking, contact your licensed health professional to individualize the amounts for your needs.
Calcium is an extremely beneficial mineral, but the requires the assistance of other vitamins and minerals to be put to beneficial use.