An international team of researchers that reviewed data from several trials found that taking calcium supplements was linked to a higher risk of heart attack and other cardiovascular events; the authors called for new research to re-assess the role of calcium supplements in the treatment of osteoporosis.

In the 29 July online issue of the BMJ you can read a report on how Dr Ian Reid, a professor of Medicine at the University of Auckland in New Zealand, and colleagues from the University of Aberdeen in the UK and Dartmouth Medical School in the US, found that people taking calcium supplements had between 27 and 31 per cent higher risk of heart attack than counterparts who took placebo.

Reid and colleagues also found smaller, but non-significant, increases in the risk of stroke and death.

Many older people take calcium supplements for osteoporosis. This is probably because research shows calcium supplements may marginally reduce the risk of fracture, and most guidelines suggest people make sure their diet contains enough calcium as a way to protect against or manage osteoporosis, wrote the researchers in their background information.

But a recent trial found calcium supplements may increase the rate of heart attack (myocardial infarction) and cardiovascular events in healthy older women, so Reid and colleagues decided to investigate further by conducting a meta-analysis (a study that pools and re-analyzes results from lots of other studies and as if they belonged to one giant study).

They searched established sources for published reports of trials that met their criteria. The trials had to be randomized, placebo-controlled trials that ran for at least one year and examined the effect of calcium supplements (dose of 500 mg per day or higher) on at least 100 participants of average age of 40 years.

They found 15 trials that matched their criteria: 5 had patient-level data covering over 8,000 participants over a median follow-up of 3.6 years, and 11 had trial-level data covering nearly 12,000 participants and a mean duration of 4 years.

For the 5 studies that yielded patient-level data, the researchers found:

  • A 31 per cent higher risk of heart attack in the people who took calcium supplements compared to those who took placebo (143 on calcium versus 111 on placebo; hazard ratio HR 1.31, 95 per cent confidence interval CI ranged from 1.02 to 1.67, statistical significance P=0.035).
  • An increase in stroke risk, but this was not significant (HR 1.20, 95% CI 0.96 to 1.50, P=0.11).
  • Non-significant increases in risk of death and a composite end-point comprising sudden death, heart attack or stroke.

For the 11 studies that yielded trial-level data, they found a similar pattern:

  • 27 per cent higher risk of heart attack in the people who took calcium supplements compared to those who took placebo (166 vs 130, pooled relative risk 1.27, 95% CI 1.01 to 1.59, P=0.038).

Reid and colleagues concluded that:

“Calcium supplements (without coadministered vitamin D) are associated with an increased risk of myocardial infarction.”

They found the results were independent of age, sex, and type of supplement and consistent across trials.

Although the risk they found was not large, because so many people take supplements it could mean a large burden of disease in the population as a whole, warned the authors.

Other studies have shown that people with high calcium intake that comes from their diet as opposed to supplements do not have a higher risk of heart attack or stroke, suggesting that perhaps the risk is limited to supplements.

Given that calcium supplements only modestly improve bone density and prevent fracture, their role in the management of osteoporosis should be re-assessed, urged the authors.

In an accompanying editorial, John Cleland a cardiology professor at the University of Hull in the UK, and colleagues, wrote that as a general rule, people with osteoporosis should only receive calcium supplements, either alone or with vitamin D, if they are also undergoing effective treatment for osteoporosis.

“Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis.”
Mark J Bolland, Alison Avenell, John A Baron, Andrew Grey, Graeme S MacLennan, Greg D Gamble, Ian R Reid.
BMJ, 2010;341:c3691; Published online 29 July 2010

Additional source: American Academy of Neurology.

Written by: Catharine Paddock, PhD