MONDAY, Feb. 9 (HealthDay News) -- In yet another blow to the dietary supplement industry, researchers find no evidence that multivitamin use helps older women ward off heart disease and cancer, the top two killers of women, respectively.

"Women can be encouraged by the fact that these vitamins seem to do no harm, but they also seem to confer no benefit," said study co-author Sylvia Wassertheil-Smoller, a professor of epidemiology and population health at Albert Einstein College of Medicine in New York City. "The kind of vitamins you get from diet is quite different, because foods are very complex and have a lot of chemicals we don't know about that interact with each other. [Eating a varied diet] is not the same as distilling it into a pill. The message is to eat a well-balanced diet, exercise and maintain weight."

Other recent studies have suggested that supplement forms of vitamins B, C, D and E, along with folic acid and beta carotene, don't seem to have cancer-fighting abilities, especially in women.

And just last week, other researchers reported that many healthy U.S. children and teenagers may be popping vitamins and mineral supplements they don't need, even while children who may actually need the supplements aren't getting them.

However, all these findings, including the latest one, come with a caveat from another expert.

"There are a lot of variables associated with this study, and unless there is an actual randomized, controlled trial, we can't say anything," said Rajat Sethi, an assistant professor of pharmaceutical sciences at Texas A&M Health Science Center Irma Lerma Rangel College of Pharmacy in Kingsville. "There have been a mixture of studies where vitamins indeed have indirectly shown benefit."

And Andrew Shao, vice president for scientific and regulatory affairs at the Council for Responsible Nutrition, stated, "Multivitamins, like all other dietary supplements, are meant to be used as part of an overall healthy lifestyle; they are not intended to be magic bullets that will assure the prevention of chronic diseases, like cancer... From a practical standpoint, this study does not change the fact that the majority of consumers could benefit from taking an affordable multivitamin, particularly as the majority of Americans fail to consume the recommended amounts of a variety of essential nutrients established by the Institute of Medicine."

According to background information in the study, which was published in the Feb. 9 issue of Archives of Internal Medicine, half of Americans regularly use dietary supplements, to the tune of $20 billion a year.

Many people believe multivitamins will prevent chronic conditions such as cancer and heart disease. Yet "convincing scientific data . . . are lacking," the researchers stated.

Two exceptions are folic acid use in women of childbearing age to prevent neural tube defects in babies, and avoiding beta carotene supplements if you're a smoker.

These researchers looked at 161,808 postmenopausal women participating in the government-sponsored Women's Health Initiative who were followed for about eight years. Some 41.5 percent of participants reported using multivitamins.

There appeared to be no association between multivitamin use and risk of breast, colorectal, endometrial, lung or ovarian cancers; cardiovascular disease; or overall death.

"There was some hint that stress vitamins, which are mostly high doses of B vitamins, may have been protective for some forms of cardiovascular disease," Wassertheil-Smoller said.

And the study does come with other caveats, Wassertheil-Smoller said.

"Most of the women in the study probably did eat a fairly decent diet, meaning we don't yet necessarily know how vitamins affect women eating poorly," she said. "The other thing is we didn't measure other things about diet such as sense of energy and well-being."

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• Cancer
• Dietary Supplements
• Heart Disease in Women