Vitamins sit on the shelf of a CVS pharmacy.
Vitamins sit on the shelf of a CVS pharmacy. - 
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Kai Ryssdal: Most of us know that you can, in fact, get too much of a good thing.

Today, the Archives of Internal Medicine gave us the science -- at least as it relates to dietary supplements. Daily multivitamins and minerals might actually do more harm than good, the research shows.

Kind of disheartening, given that we spend $28 billion a year on all that stuff. Jennifer Collins reports has the story.

Jennifer Collins: By some estimates, as many as half of all Americans take some kind of supplement. And the habit starts early. Remember this jingle?

Flintstones vitamins ad: We are Flintstones Kids, 10 million strong and growing.

Susan Fisher chairs the Department of Preventive Medicine at the University of Rochester. She says its in our nature to go overboard.

Susan Fisher: In America, we have the tendency to think, 'gee, if one vitamin pill is good, maybe I'll take two today because I didn't eat very well.'

But more isn't better. The new study looked at nearly 40,000 older women over a two-decade period. Researchers found women who took multivitamins or iron were slightly more likely to die during that period.

Jaakko Mursu is the lead author of the study. He says the increase in risk wasn't dramatic, but:

Jaakko Mursu: People think or they take supplements that they would get benefits, so this is contrary to that belief.

Mursu says more studies are needed to know whether other factors, like illness, played a role in the deaths. Studies like this have done little to dent the supplement business.

Steve Mister heads an industry group that represents the supplement makers.

Steve Mister: People look at supplements as kind of an insurance policy that they're getting all the nutrients that they need.

Mister says sales continued to rise, even during the recession.

I'm Jennifer Collins for Marketplace.

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