Popping vitamin E and beta-carotene pills every day will not ward off heart attacks or strokes and may even be harmful in some cases, doctors say.

Antioxidants such as vitamin E are among the best-selling vitamins. Early lab and small studies on humans suggested the pills may prevent heart attacks and premature death. Larger, long-term randomized studies have called the claims into question.

Researchers at the Cleveland Clinic Foundation analysed the polled results from 15 clinical trials involving nearly 220,000 people.

Each trial involved at least 1,000 patients who were followed from one to 12 years.

"We now have the clinical evidence needed to actively discourage the use of vitamin supplements containing beta-carotene due to the significant excess in overall mortality and cardiac death," said study investigator Dr. Marc Penn, a Cleveland Clinic cardiologist.

The researchers concluded vitamin E did not reduce death from cardiovascular disease and did not lower the incidence of stroke. Beta-carotene was linked to a 0.4 per cent increase in all causes of death and a 0.3 per cent rise in cardiovascular death.

Most of the participants either already had heart or blood vessel disease or were at increased risk. Seven studies looked at vitamin E alone or in combination with other antioxidants. Eight involved beta-carotene alone or with other antioxidants.

Last month, another team reviewed the scientific evidence on the safety of 34 common vitamins and minerals. Britain's Foods Standards Agency then warned vitamin and mineral supplements can often do more harm than good and shouldn't be taken in high doses.

Some nutrition experts think antioxidants work when found in foods, not pills. They say people should be able to get enough beta-carotene by eating yellow, orange and leafy green vegetables and vitamin E from nuts, seeds and plant oils.

The U.S. study appears in the June 14 issue of the medical journal The Lancet.