Middle-aged and older men who took a multivitamin daily for several years did not have a reduced risk of suffering a heart attack, a large U.S. study released today finds.

The long-term health benefits of taking vitamins is uncertain, the researchers said in the study in Tuesday's issue of the Journal of the American Medical Association. However, many adults use the supplements, fuelling an industry worth billions of dollars annually.

The JAMA issue is devoted to cardiovascular disease, and includes the study of 14,641 male physicians averaging age 64 who were randomly assigned to take a multivitamin or placebo.

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The dietary supplement industry was worth an estimated $23.7 billion US in 2008. (iStock)

"Among this population of U.S. male physicians, taking a daily multivitamin did not reduce major cardiovascular events, myocardial infarctions, stroke and cardiovascular disease mortality after more than a decade of treatment and followup," Howard Sesso, an epidemiologist at Brigham and Women's Hospital and Harvard University in Boston, and his co-authors concluded.

When the study began, 754 of the men had a history of cardiovascular disease.

Over the study's duration, 1,732 men in both groups had major cardiovascular events, including 652 first heart attacks and 643 cases of stroke, and 829 men had cardiovascular death.

"These data do not support multivitamin use to prevent cardiovascular disease, demonstrating the importance of long-term clinical trials of commonly used nutritional supplements," the study's authors wrote.

"Whether to take a daily multivitamin requires consideration of an individual's nutritional status, because the aim of supplementation is to prevent vitamin and mineral deficiency, plus consideration of other potential effects, including a modest reduction in cancer and other important outcomes in Physicians' Health Study II that will be reported separately."

More rashes were reported among participants in the study who took the vitamins than in the men who took placebo.

The doctors in the study were likely well-nourished and the supplements may not have provided any extra benefits beyond their diet, the researchers said.

Combination of vitamins in food

In contrast, studies have consistently shown that people who eat more fruits and vegetables have lower rates of heart disease and stroke, which supports the idea that combinations of vitamins at moderate doses may offer protection against cardiovascular disease, they noted.

Data from multiple trials clearly confirm that cardiovascular disease can't be prevented or treated with vitamins, Dr. Eva Lonn of McMaster University and Hamilton General Hospital said in a journal editorial published with the study.

The promise of an "easy fix for multiple health problems, combined with relatively lenient regulations, fuelled the growth of the dietary supplement industry from around $4 billion US in 1994 to $23.7 billion US in 2008," Lonn wrote.

People can get most of the vitamins and micronutrients they need by eating a healthy, well-balanced diet, and many foods are already fortified, Lonn said.

She concluded that vitamins distract from the simple, proven ways of preventing cardiovascular disease: Eating healthy foods, exercising regularly and avoiding tobacco products.

The research was funded by the U.S. National Institutes of Health and BASF Corporation.

Pfizer provided the pills, which stayed the same over the study period.

Lonn has received grants or payments from several pharmaceutical companies.

Whether the findings apply to women, younger men, or those who were less healthy than the physicians participating in the study isn't known. The research was also presented at the American Heart Association's  Scientific Sessions.