Taking a daily multivitamin does not reduce the risk of heart disease for older men, according to data from a large study presented on Monday.

About half of US adults take at least one daily dietary supplement, the most popular being a multivitamin, according to the US Centers for Disease Control and Prevention.

The US Physicians Health Study II monitored nearly 15,000 male doctors aged 50 and older for more than 10 years. Participants were randomly assigned to take a multivitamin or a placebo.

"We found that after more than a decade, there is neither benefit nor risk," in terms of cardiovascular disease, said Dr Howard Sesso, study author and associate epidemiologist at Brigham and Women's Hospital in Boston.

Researchers reported last month that the same trial showed that a daily multivitamin reduced the men's overall risk of cancer by 8 per cent.

"We still feel very comfortable with the conclusions for the cancer findings," Dr Sesso said. "The lack of effect for cardiovascular disease versus cancer benefit isn't necessarily inconsistent. There could be a difference in mechanism of effect."

The findings were presented in Los Angeles at the American Heart Association scientific meeting and published in the Journal of the American Medical Association.

"It is hard for us to recommend, at this point in time, taking a multivitamin to avoid cardiovascular disease," Dr Sesso said, noting that patients need to discuss all over-the-counter medicines with their doctors.

He said patients often view multivitamins as a "quick fix," which can lead them to let up on other efforts to improve their health.

"The danger of taking multivitamins is that it will lead you to think you can forgo other lifestyle changes," such as not smoking and maintaining a healthy diet, said Dr Dariush Mozaffarian, associate professor in the department of epidemiology at Harvard School of Public Health.

The research was funded by the National Institutes of Health and with a grant from BASF Corporation. The multivitamins and packaging were provided by BASF, Pfizer Inc and DSM Nutrition Products.

"Many patients think that because they are getting an OTC (over-the-counter) medication it is safe and the risk of complications is low," said Dr Elliott Antman, chairman of the AHA Scientific Sessions Committee and professor of medicine at Harvard Medical School. "That appears to be right, but we still need to remind them of the need for lifestyle changes."

Two other studies involving Omega-3 fatty acids derived from fish oil that were presented at the meeting on Monday also failed to help specific heart conditions.

In one, taking fish oil for a year failed to limit recurrent symptomatic atrial fibrillation, a type of irregular heartbeat that significantly raises the risk of stroke.

In the other trial, short term use of fish oil failed to decrease incidence of atrial fibrillation that commonly occurs after patients undergo heart surgery.

Dr Peter Wilson, from the Emory University School of Medicine in Atlanta who was not involved in the studies, was disappointed by the results.

Every time we've looked at Omega-3, he said, "We've come up short. It's very discouraging." – Reuters