Calcium supplements may increase the risk of heart attacks for older women

Scientists in New Zealand say healthy post-menopausal women who take calcium supplements to maintain bone strength may be increasing their risk of heart attacks.

The researchers from the University of Auckland say this increased heart attack risk could outweigh the benefits to the bones from calcium supplements.

It is quite common for older women to take calcium supplements in order to prevent osteoporosis, a condition in which bones become weak and brittle, leading to fractures.

The researchers led by Ian Reid conducted a study involving 1,471 healthy post-menopausal women, aged 55 years or over who had previously taken part in a study to assess the effects of calcium on bone density and fracture rates.

Of the group 732 were given a daily calcium supplement and 739 were given a placebo and were monitored every six months for a five year period.

The researchers found that heart attacks were more common in the women taking the calcium supplements, with 31 women who took supplements experiencing a heart attack, compared to 21 women who were given a placebo.

Because of the potential importance of the findings, the researchers checked hospital admissions and reviewed all death certificates for study participants to identify any unreported events.

The scientists say previous research has suggested that taking calcium supplements might protect against vascular disease by lowering levels of bad cholesterol in the blood, but the calcium supplements raised blood calcium levels; they say this possibly accelerates the formation of deposits in the arteries that could lead to heart attack.

While the researchers say their results "are not conclusive" they suggest that high calcium intakes might have an adverse effect on vascular health and need to be confirmed by other studies.

The research is published in the British Medical Journal and on bmj.com.