How much caffeine in that supplement? Hard to tell

Some of these products—also sold at health-food stores across the county—didn't provide any information about caffeine on their labels despite being packed with it, and others had more or much less caffeine than their labels indicated.

"Fewer than half of the supplements had accurate and useful information about caffeine on the label," said study lead author Dr. Pieter Cohen, assistant professor of medicine at Harvard Medical School. "If you're looking for these products to help ... your performance, some aren't going to work and you're going to be disappointed. And some have much more caffeine than on the label."

Researchers launched the study, funded by the U.S. Department of Defense, to add to existing knowledge about how much caffeine is being consumed by members of the military. Athletes and members of the military, they said, face a risk of health problems when they consume too much caffeine and exercise in the heat.

Cohen emphasized that the supplements were purchased in civilian stores: "Why is it that 25 percent of the products labels with caffeine had inaccurate information at a mainstream supplement retailer?"

He also explained the specific military concern.

"We already know that troops are drinking a lot of coffee and using a lot of energy drinks and shots," Cohen said. "Forty-five percent of active troops were using energy drinks on a daily basis while they were in Afghanistan and Iraq. We're talking about large amounts of caffeine consumed, and our question is: What's going on on top of that?"

In the worst-case scenario, people could become jittery and even develop rapid heartbeats if they use the supplements in conjunction with other caffeine products such as energy drinks or coffee, said Dr. John Higgins, who studies caffeine as the chief of cardiology at Houston's Lyndon B. Johnson General Hospital.

The study has some holes, however. For one, it didn't identify the 31 supplements that it examined. The researchers said only that they're the most popular supplements sold as pills on military bases with labels that indicate that they include either caffeine or herbal ingredients that include caffeine.

Of the 31 supplements, 20 listed caffeine on their labels. Of those 20, only nine correctly listed the amount, according to the researchers. Five listed amounts between 27 percent and 113 percent off from the actual amount.

Six products listed caffeine as an ingredient but didn't say how much. The researchers found that they had 210 to 310 milligrams per serving—the same amount that is in two to three cups of coffee.

People often drink coffee or take energy supplements to become more alert, and Cohen said it's true that the caffeine in two to three cups of coffee can improve performance. But people lose the boost at about five cups, he said.

What to do? Higgins, the Texas cardiologist, said manufacturers need to be required to state properly how much caffeine is in supplements, and the amounts need to be independently verified.

Another expert said that giving consumers consistent, accurate information could benefit their health.

"If consumers had a better idea about how much caffeine they were getting from various sources—from energy drinks and supplements—they would count it up. They would take notice and realize that they may be overdoing it," said pharmacist Philip Gregory, editor of the Natural Medicines Comprehensive Database.

The study appeared in the Jan. 7 issue of the journal JAMA Internal Medicine.

More information: For more about supplements, try the U.S. National Library of Medicine.

Journal reference: JAMA Internal Medicine

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