Vitamin supplements -- taken by millions of Americans to boost or maintain their health -- don't reduce the risk of heart attacks, strokes or breast cancer, according to two large studies published today.
In one of the trials, 14,641 middle-aged male physicians took vitamins E and C for an average of eight years but did not see any benefit to their cardiovascular health.
The other study tracked 36,282 postmenopausal women for an average of seven years and found that a daily regimen of vitamin D and calcium did not offer any protection against invasive breast cancer.
Almost half of all adults in the U.S. take vitamins daily, but the results should prompt some of them to reconsider their rationale for doing so, said Howard Sesso, who led the cardiovascular disease study appearing in the Journal of the American Medical Assn.
"You don't know whether something is really true until you test it in one of these large-scale, long-term clinical trials," said Sesso, an epidemiologist at Brigham and Women's Hospital in Boston and a professor at Harvard Medical School.
But Dr. David Heber, director of the UCLA Center for Human Nutrition, said the studies didn't prove vitamins were useless, especially considering that observational studies and experiments with animals had produced mixed results.
"Absence of evidence is not evidence of absence," said Heber, who was not involved with the latest studies.
The heart study was prompted by basic research showing that antioxidants such as vitamins E and C kept the formation of atheroschlerotic plaque in check and helped prevent tissue damage that causes cardiovascular disease.
Sesso's team tested the effect of 400 international units, or IUs, of vitamin E every other day and 500 milligrams of vitamin C daily. Doctors who participated in the study received either both vitamins, one vitamin and one placebo, or two placebos.
Among the 7,315 people who took vitamin E, there were 620 cases of heart attacks, strokes and deaths from heart disease compared with 625 such cases among the 7,326 people who took the dummy pills, the study said.
The only difference the researchers found was a 74% increase in hemorrhagic strokes among those who took vitamin E, though Sesso said that the strokes were rare in both groups and that the finding could have been a fluke.
