BOSTON—Dietary supplements sold on military bases often have misleading labels, and the amount of caffeine they actually contain can vary widely, according to a recent study.

Unknown caffeine levels can especially be a problem when the supplements are combined with other caffeine sources, such as energy drinks or coffee, according to the authors.

“Excessive caffeine consumption, particularly when combined with other stimulants, may increase the risk of hypokalemia, rhabdomyolysis, and other heat-related injuries among athletes and military personnel,” according to the research letter published by JAMA Internal Medicine.

“Caffeine is consumed in a wide range of popular items including coffee, teas, sodas, energy drinks, energy gels, chocolate, gums, and over-the-counter medications,” the authors point out. “Dietary supplements, which are commonly consumed by military personnel are a poorly characterized source of caffeine. Only with accurate information about the quantity of caffeine in dietary supplements can consumers and clinicians be assured of safe use.”

The researchers from Harvard Medicine School analyzed the caffeine content of 31 dietary supplements sold on military bases that are known to either have added caffeine or herbal ingredients that naturally contain caffeine.

Of the 11 supplements that listed herbal ingredients, all had either no caffeine or only traces of the substance. With the other 20 products:

• Nine had labels with accurate caffeine information;
• Five had caffeine levels much lower or higher than the amounts listed on their labels;
• Six didn’t list caffeine on their labels but had very high amounts of between 210 and 310 mg per serving, two to three times an eight-ounce cup of coffee.

“Our chemical analysis of the caffeine content in dietary supplements popular on military bases found that less than half of the analyzed supplements’ labels provided clinically useful information regarding caffeine,” the authors write.

They note that a limitation of the study was that researchers tested only one sample of each supplement.

Suggesting that “the law regulating the manufacturing and sales of dietary supplements in the United States has loopholes that allow manufacturers to avoid listing the quantity of caffeine on the label,” the authors conclude, “Given the lenient legal framework and inaccurate labels, military personnel are unable to determine if a supplement can be safely combined with other products or foods containing caffeine.”

An accompanying editor’s note from Mitchell H. Katz, MD, called the research letter “provocative,” noting, “Recent media reports of deaths related to consumption of drinks high in caffeine¹ remind us that substances that are safe and even beneficial at usual doses (how many of us would have survived residency without caffeinated beverages?) may be harmful when consumed to excess.”

Katz added, “This report contributes to other reports in this journal and other journals indicating that to protect the public we need tighter regulation of dietary supplements.”