People who take calcium supplements could be increasing their risk of a heart attack by as much as 30%, according to study published today online by the BMJ.
The researchers have called for a reassessment of the role of calcium supplements, which are often taken by older people for osteoporosis, in managing that condition.
Almost three million people in the UK are thought to have osteoporosis and calcium supplements are commonly prescribed for skeletal health.
A recent trial, however, suggested the supplements might increase rates of heart attack and cardiovascular events in healthy older women.
An international team of researchers from the UK, New Zealand and the USA wanted to investigate this issue further and analysed the results of 11 randomised controlled trials of calcium supplements (without co-administered vitamin D) involving 12,000 patients.
Differences in study design and quality were taken into account.
The researchers found that calcium supplements were associated with about a 30% increased risk of heart attack and smaller, non-significant, increases in the risk of stroke and mortality.
The findings were consistent across trials and were independent of age, sex, and type of supplement.
Previous studies have found no increased cardiovascular risks with higher dietary calcium intake, suggesting that the risks are restricted to supplements.
The authors said: “Although the magnitude of the increase in risk is modest, the widespread use of calcium supplements means that even a small increase in incidence of cardiovascular disease could translate into a large burden of disease in the population.”
Given the modest benefits of calcium supplements on bone density and fracture prevention, a reassessment of the role of calcium supplements in osteoporosis management is warranted, they conclude.
An accompanying editorial by experts from the University of Hull and University of Leeds, suggests that while uncertainty exists about whether the increase in heart attack and stroke is real, there are also doubts about the efficacy of calcium supplements in reducing fractures.
On the basis of the limited evidence available, patients with osteoporosis should generally not be treated with calcium supplements, either alone or combined with vitamin D, unless they are also receiving an effective treatment for osteoporosis for a recognised indication.
They also believe that research on whether such supplements are needed as an adjunct to effective agents is urgently required.
The British Heart Foundation (BHF) said caution was needed over the calcium supplement research results.
BHF senior cardiac nurse, Judy O'Sullivan, said: “We need to be cautious about the results of this analysis because none of the studies involved were designed to look specifically at the relationship between calcium supplements and the risk of heart attack.
“However, the research should not be completely ignored. Any new guidelines on the prevention of fractures in those most vulnerable to them should take this type of analysis into account.
“Anyone who has been advised by their doctor to take calcium supplements shouldn’t stop because of this research alone.”