People should stop wasting their money on dietary supplements, some physicians said today, in response to three large new studies that showed most multivitamin supplements are ineffective at reducing the risk of disease, and may even cause harm.

The new studies, published today (Dec. 16) in the journal Annals of Internal Medicine —including two new clinical trials and one large review of 27 past clinical trials conducted by the U.S. Preventive Services Task Force — found no evidence that taking daily multivitamin and mineral supplements prevents or slows down the progress of cognitive decline or chronic diseases such as heart diseases or cancer.

"The message is simple: Most supplements do not prevent chronic disease or death, their use is not justified and they should be avoided," the physicians wrote in an editorial published along with the studies.

This message is especially aimed at people who have no signs of nutritional deficiency — meaning most supplement users in the United States, the researchers said.

"Study after study comes back negative — yet people continue to take supplements, now at record rates," said Dr. Edgar Miller, one of the five authors of the editorial and a professor of medicine and epidemiology at Johns Hopkins University in Baltimore.

There may be a psychological component to taking supplements, Miller said. Despite evidence showing supplements hold no benefit for the general population, some people may rationalize they need supplements because their diets lack necessary nutrients, Miller told LiveScience.

The new findings are in line with those of previously published studies that have found no benefits from dietary supplements, including B vitamins and antioxidants, and even suggested possible harms. Results of clinical trials involving tens of thousands of people have shown that beta-carotene, vitamin E and possibly high doses of vitamin A supplements actually increase death rates, the researchers said.

"We believe that the case is closed — supplementing the diet of well-nourished adults with most mineral or vitamin supplements has no clear benefit and might even be harmful," the researchers wrote in their editorial.

The use of multivitamin and mineral supplements among Americans has increased to about 50 percent in the mid-2000s, up from 40 percent in the early 1990s, according to the Centers for Disease Control and Prevention.

For some supplements, such as beta-carotene and vitamin E, studies have found declines in use, following reports of their negative effects on lung cancer and mortality.

In contrast, sales of multivitamins and other supplements have not been affected by major studies that didn't find benefits, the researchers said. The U.S. supplement industry continues to grow, and reached $28 billion in annual sales in 2010. Similar trends have been reported in the United Kingdom and in other European countries.

The dietary-supplement industry maintains that for many Americans, diet alone may not provide the necessary vitamins they need daily, Miller said.

"The industry tries to create the impression that we are deficient, but randomized trials show that we are not all deficient and we don't benefit from supplements," Miller said, adding that clinical trials include people with varied diets from the general population.

The new review study looked at clinical trials that included a total of 450,000 older adults. All together, the researchers didn't find clear evidence of a beneficial effect of supplements on cancer and heart diseases.

In another study, researchers looked at the effects of taking a daily combination of nutrients —including vitamins A, C, E, beta-carotene and B vitamins — in 6,000 men ages 65 and older who were followed for 12 years. The cognitive performance and verbal memory of participants who took multivitamin supplements didn't differ from those of participants who took placebo.

In the third study, the researchers examined whether high doses of multivitamins and minerals could prevent heart attacks, strokes and death in 1,700 people who have already had a heart attack. After an average follow-up of five years, the results didn't show a difference between participants who took dietary supplements and those who didn't.

Email Bahar Gholipour or follow her @alterwired.

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