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Dangers of Dietary Supplements: A Closer Look continued...

The possible problems listed for each are based on either case reports or clinical research, Metcalf tells WebMD. The report updates a previous investigation on supplements done by Consumer Reports, Metcalf says. The publication thought it important to update the information, she says, as ''half the adult population takes some supplement."

In 2009, more than $26 billion was spent in the U.S. on supplements, according to the Nutrition BusinessJournal, a trade publication. In the last five years, supplement sales have increased by nearly 6% a year, according to Carla Ooyen, a spokeswoman for the publication.

Despite the popularity of supplements, Metcalf says, "You need to be extremely careful about buying nutritional supplements, because there are several different ways they can be harmful."

Some supplements, she says, include ingredients that can be ''inherently harmful" and lack proof of effectiveness.

In other cases, manufacturer error may lead to excess amounts of ingredients in products. That was the case for a Tennessee man who took a supplement and experienced diarrhea, joint pain, hair loss, lung problems, and had fingernails and toenails fall off. In his case, detailed in the report, an inspection of the supplement maker's facilities found the samples had more than 200 times the labeled amount of selenium and up to 17 times the recommended intake of chromium, according to the report, citing FDA information.

Dietary supplements are regulated under the Dietary Supplement and Health Education Act of 1994. Under an amendment effective in 2007, manufacturers are now required to report serious adverse events.

But Metcalf and others think the FDA needs more regulatory power. ''The FDA should be given more power to yank these things form the market [when found ineffective]," Metcalf says.

Dietary Supplements: Industry Views

The report is termed ''a little bit sensationalized" by Andrew Shao, PhD, a spokesman for the Council for Responsible Nutrition, a trade group.

"Any time you pick adverse experiences from a handful of individuals, you know it is being sensationalized,” he says. “It doesn't represent the totality of the evidence."

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