Multivitamins do not have any impact on postmenopausal women's risk of dying, getting cancer or cardiovascular disease, said the most extensive study to date on the subject, released Monday.
The research examined 161,808 women, age 50 to 79, who took part in clinical trials on hormone therapy, dietary modification and vitamin D supplements, as well as 93,676 women who were part of an observational study.
"Analyses revealed no significant associations between multivitamin use and the likelihood of developing cancer or cardiovascular disease, or of dying," said the findings, published in the Archives of Internal Medicine.
In all, 41.5 percent of participants took multivitamins over a period of about 15 years.
The authors of the study pointed out that about half of Americans take vitamin supplements, even though there is little evidence to back up the health benefits of the 20-billion-dollar per year industry.
"The motivations for supplement use vary, but common reasons include the belief that these preparations will prevent chronic diseases, such as cancer and cardiovascular disease," wrote the authors of the study led by Marian Neuhouser of the Fred Hutchinson Cancer Research Center in Seattle, Washington.
"These views are often fueled by product health claims, consumer testimonials and an industry that is largely unregulated."
The only exception the researchers found related to "a possible lower risk of myocardial infarction (heart attack) among users of stress-type supplements.
"Many stress supplements include high doses of folic acid and other B vitamins; previous studies have supported a protective role for folic acid in relation to cardiovascular disease and its antecedent risk factors."
The researchers recommended that "nutritional efforts should remain a principal focus of chronic disease prevention ... but without definitive results from a randomized controlled trial, multivitamin supplements will not likely play a major role in such prevention efforts."