Vitamin D supplements may help to reduce the risk of heart disease.

Researchers found that women over age 65 who took the supplements had nearly one-third less risk of dying from heart disease.

Low levels of certain forms of vitamin D have been associated with increased risk of heart attacks.

But the positive impact of taking vitamin D supplements has not been previously examined.

Vitamin D and calcium are part of the standard therapy for the bone-thinning disease osteoporosis.

A team from the University of California at San Francisco studied 9,704 women aged 65 and older. Of these, 4,272 were taking vitamin D supplements.

Over a period of nearly 11 years, 420 of the women died of coronary heart disease (CHD).

Women who used vitamin D supplements had a 31% lower risk of heart disease death than those who did not take the supplements.

Calcium link

Vitamin D is one of the most important regulators of calcium absorption in the body.

Atherosclerosis, the accumulation of cholesterol and fat in the walls of arteries, is often associated with calcification, the build up of the mineral calcium in the arteries.

It is thought that low levels of vitamin D in the blood are associated with an acceleration of this build up.

Women with osteoporosis - which is caused by loss of calcium from the bones - are more likely to die of CHD than women without the disease.

Researcher Dr Paul Varosy said: "It is possible that the same hormonal processes that lead to calcium loss from bones may somehow lead to accumulation of calcium in atherosclerotic plaques."

A spokesman for the British Heart Foundation said a major study published last year had found no conclusive proof of a protective benefit from taking dietary supplements containing vitamins B, C or beta-carotene.

He told BBC News Online: "We need more long-term research specifically into the effects of vitamin D, but we feel it is better for people to get their vitamins from eating fresh fruit and vegetables, rather than by taking supplements."