The researchers carried out a meta-analysis: a study of studies. Essentially, they searched for previous studies of calcium supplementation (compared with a placebo) and compiled them together to try to tease out effects that each single study may not have detected. Overall, the researchers ended up analyzing 11 studies between 1990 and 2007, for a total of 12,000 participants. In all the studies, 143 people who were taking calcium supplements had a myocardial infarction (a heart attack), compared with 111 people who were taking the placebo. This represents an increase in the risk of myocardial infarction of 31% for those taking calcium supplements. Interestingly, calcium supplements were only associated with an increased risk of myocardial infarction in people who already had a big calcium intake through their diet (more than 805 mg/day).
This study will no doubt shake things up in the fields of cardiovascular health and osteoporosis prevention. However, there is one important caveat with this analysis: the researchers did not look at studies where the supplement was a combination of calcium and vitamin D. Therefore, one cannot assume that calcium/vitamin D supplements would lead to the same risks. In fact, another recent study in women reported that calcium and vitamin D administered together had no effect on the risk of heart disease. It’s also important to remember that when weighing risks and benefits, calcium (and vitamin D) does a lot more than just strengthen your bones: it has also been shown to play a role in the prevention of certain cancers.
One thing is for sure: dietary calcium intake is safe. So go ahead and enjoy the moo juice.
*You’ll be pleased to hear that I am dedicating my postdoctoral training to solving the puzzle.
Reference: Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. (2010) Bolland et al. British Medical Journal [Epub ahead of print].