Calcium supplements and the risk of MI?

The meta-analysis to investigate whether the calcium supplements increase the risk of cardiovascular events published recently in BMJ(1) has concluded that Calcium supplements (without coadministered vitamin D) are associated with an increased risk of myocardial infarction. As calcium supplements are widely used these modest increases in risk of cardiovascular disease might translate into a large burden of disease in the population. A reassessment of the role of calcium supplements in the management of osteoporosis is warranted.
The findings of the meta-analysis were consistent across trials, with an increased relative risk of myocardial infarction with calcium observed in six of the seven trials in which at least one event occurred, although no individual trial reported a statistically significant effect. The risk of myocardial infarction with calcium tended to be greater in those with dietary calcium intake above the median but was independent of age, sex, and type of supplement
The studies that compared coadministered calcium and vitamin D supplements with placebo were not included. The results therefore may not apply to coadministered calcium and vitamin D supplements.
In an editorial accompanying the article, Dr John Cleland and colleagues (2) wonder why calcium supplements should increase cardiovascular risk, as found in this meta-analysis. "Accumulation of calcium in the arterial wall leading to reduced compliance would be expected to take years, but the increased risk of myocardial infarction reported by Bolland and colleagues occurred early after calcium supplementation (median follow-up of 3.6 years)." They suggest that the increased risk of MI may not be a true effect, because the increased risk of MI was not accompanied by an increase in mortality. "Calcium supplements could simply be causing gastrointestinal symptoms that could be misdiagnosed as cardiac chest pain
It was concluded that patients with osteoporosis should generally not be treated with calcium supplements, either alone or with vitamin D, unless they are also receiving an effective treatment for osteoporosis for a recognized indication." They add that research on whether such supplements are needed in addition to effective osteoporosis treatment is "urgently required".
1. http://www.bmj.com/content/341/bmj.c3691.long
2. http://www.bmj.com/content/341/bmj.c3856.long