The findings you’re referring to came from an analysis of 11 earlier trials that looked at people who had been randomly assigned to take calcium supplements. This "meta-analysis" published online in July, 2010, concluded that taking supplemental calcium increased the likelihood of heart attack among people over 40. The researchers, from the University of Auckland in New Zealand, chose the studies to include and then performed the review. Their results suggested that the supplements appeared to have only a minor beneficial effect on bone health and that on the basis of these findings they now advise their own patients to avoid them and instead place more emphasis on calcium-rich foods in their daily diets. They speculated that supplements might increase blood levels of calcium above normal, causing changes in blood chemistry that could be dangerous to individuals at risk for heart attacks.
Interestingly, the researchers saw no increase in stroke or death from heart disease in the meta-analysis, and in none of the studies analyzed did participants take vitamin D as well as calcium. Vitamin D is essential to calcium absorption and deficiencies are widespread.
Because they combine data from studies that were originally designed to look at something else, meta-analysis can only ask questions, not answer them. My feeling is that, if anything, this analysis may warrant looking more closely at vitamin D deficiency, not just calcium supplements. In news reports of this investigation, I was interested to see that some cardiologists were puzzled as to why an increased risk of heart attacks (20 to 30 percent) showed up but no increased risk of stroke and no increase in deaths from heart disease. In fact, John Cleland, M.D., a cardiologist in England, wrote an editorial accompanying the meta-analysis that said, in part, "It is not clear whether they (calcium supplements) really increase the risk of heart attacks or strokes."
Alarming as these findings appear to be, I wouldn’t worry about them or stop taking calcium supplements because of them. I still recommend that women supplement with no more than 500 to 700 mg of calcium citrate in two divided doses taken with meals for a total of 1,000-1,200 mg from all sources (including diet). I also recommend that everyone take a daily supplement of 2,000 IU of vitamin D, a micronutrient essential to bone mineralization, which may prevent or slow the progression of osteoporosis. Vitamin D also helps to strengthen the immune system and reduces risk of fractures. What’s more, research indicates that vitamin D may provide protection against hypertension, psoriasis, several autoimmune diseases (including multiple sclerosis and rheumatoid arthritis), and many forms of cancer. And new findings suggest that it also reduces the risk of heart disease.
Andrew Weil, M.D.