Patti Kiernan enrolled in a focused exercise program in Dallas after her doctor said her bone density had dropped to osteoporosis levels. Researchers also advise people to use exercise to prevent bone thinning. (Donna McWilliam/Associated Press)

The value of taking calcium supplements to ward off the degenerative bone disease osteoporosis has been called into question by a report that suggests the practice could lead to an increased risk of heart attacks.

It's standard medical advice for people to take calcium supplements if they are not getting the recommended intake of calcium in their diet every day.

But a new review of studies, published Friday in the British Medical Journal, has suggested a higher risk of heart attacks may result.

A recent study suggested a link between calcium and heart attacks, so researchers from the University of Auckland, New Zealand, reviewed 11 studies of people taking calcium, without also taking vitamin D, which included almost 12,000 people.

Prof. Ian Reid of the university's department of medicine says differences in study design and quality were taken into account to minimize bias.

His review found that calcium supplements were associated with an increased risk of heart attack and smaller, non-significant, increases in the risk of stroke and mortality.

Of the 6,166 participants who received calcium supplements, 166 experienced a myocardial infarction (heart attack), compared with 130 out of 5,805 in the placebo group. This translates to about a 30 per cent increased risk.

Population risk

The findings were consistent across trials and were independent of age, sex and type of supplement.

Reid says that although the increase was modest, it could translate into large numbers across the population.

But experts from Osteoporosis Australia have cast doubt on the findings. In a statement on their website, it says the weight of evidence to date indicates no increased risk of heart attacks from taking calcium supplements.

They say a number of long-term studies have found that calcium can actually protect the heart, such as the Nurses Study of 85,000 women.

Osteoporosis Australia says calcium supplements are an effective way of reducing fracture risk and bone loss in older men and women who have a diet low in calcium.

Reassess role of supplements

Ultimately, any potential risks of calcium need to be weighed against the benefits of the supplements to prevent osteoporosis.

"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," says Reid.

An accompanying editorial by Prof. John Cleland of the University of Hull, England, and colleagues suggests there are doubts about the efficacy of calcium supplements in reducing fractures.

He says that on the basis of 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 other treatments for osteoporosis.

The researchers advised people consuming calcium supplements to seek advice from their doctors, eat more calcium-rich foods and try exercise, quitting smoking and keeping a healthy weight to prevent osteoporosis.

This review was funded by the Health Research Council of New Zealand and the University of Auckland School of Medicine Foundation. Several authors said they've studied drugs in clinical trials of calcium supplementation that were supplied by pharmaceutical companies.