Millions of women take multivitamins, often in the hope the popular supplements will prevent cancer and other diseases.
But the largest study ever conducted in post-menopausal women has found "convincing evidence" that multivitamin use has "little or no influence" on the risk of common cancers, cardiovascular disease or dying from any cause in post-menopausal women.
The research involved 161,808 American women, age 50 to 79, who are part of the ongoing Women's Health Initiative, the largest study of women's health. A total of 41.5 per cent of the women used multivitamins. The most popular was a multivitamin with minerals.
The women were enrolled in the trial between 1993 and 1998. After an average eight years of followup, researchers found no evidence multivitamins either increased or decreased the risk of cancers of the breast (invasive), colon/rectum, endometrium, ovary, kidney, bladder, stomach or lung.
They also found no significant effect on the risk of heart attack, stroke and blood clots in the veins.
There was also no association between multivitamin use and total mortality.
The findings held after researchers took body mass index, smoking, blood pressure, a history of heart disease and other factors into account.
"You don't need to take multivitamins if you want to protect yourself against cancer, heart disease or stroke. It won't do it for you," says Sylvia Wassertheil-Smoller, professor of epidemiology and population health at Albert Einstein College of Medicine in New York and co-author of the study, published this week in the journal Archives of Internal Medicine.
"Do the things you already know are protective -- exercise, maintain a healthy weight and eat a good diet."
Nearly half of Canadian women were taking vitamins in 2004, according to the most current data from Statistics Canada, and the supplements are even more popular among women 50 and older. Canadians together spend nearly $300 million annually on vitamins, with about a third of that for multivitamins, according to NDMAC, the Non-prescription Drug Manufacturers Association of Canada.
Wassertheil-Smoller says the supplements are heavily advertised, they seem harmless and people prefer "to take one little pill than do the things they know are good for them."
"Everyone is looking for a magic bullet."
But the new study is the latest in a run of bad news suggesting vitamin supplements have been oversold. Last month, researchers reported that women who take vitamin C, vitamin E or beta carotene are no less likely to get cancer than women who don't take the supplements.
In November, researchers who have been following 15,000 male doctors for 10 years reported that vitamin E and C supplements have no effect on the risk of heart attacks, stroke, cardiovascular death, cancer or congestive heart failure in middle-aged and older men.
Multivitamins are the most frequently used dietary supplement, but most studies have looked at specific vitamins. "People take Cs and Es and Ds and all kinds of single supplements," Wassertheil-Smoller says, and the results from smaller studies have been conflicting, with some showing benefits, others none.
The question has been, what if you put them together in a multivitamin supplement?
The women in the study were older, and the researchers caution against extrapolating the results to the general public.
But even when the researchers dug further, looking at fruit and vegetable intake, taking a multivitamin still didn't make a difference.
"Even if they had a diet that wasn't optimal, taking a multivitamin did not reduce their risk," of cancer or cardiovascular disease, says lead author Marian Neuhouser, of the Fred Hutchinson Cancer Research Center in Seattle. "Really, it's a kind of a wash for these particular outcomes."
Dr. Robert Hegele is a cholesterol specialist and heart researcher at the Robarts Research Institute at the University of Western Ontario.
Hegele, who treats men and women at high risk for heart attack or stroke, says that some of the same people who are reluctant to go on a prescription drug that's been proven effective will go out "and spend their own money, and sometimes a lot of money, every month on vitamin supplements with the idea, and the hope, it would reduce their risk of heart attack and stroke.
"This paper is just one piece of the puzzle, but it looks like all the data is lining up to show that taking supplements is not going to have a major impact."
-- Canwest News Service