Half of us are taking dietary supplements on a daily basis but what you may not know is that some of them come with a kick of caffeine -- and it may not even be listed on the label.

Agricultural Research Service (ARS) scientists analyzed a number of caffeine-containing products including supplements. You see, caffeine is a natural alkaloid in more than 60 plants (including tea and coffee) and in plant derivatives known as "botanicals." These botanicals, such as guarana, yerba mate, kola nut, and green tea extract, are common dietary-supplement ingredients and are printed on the label's ingredient list -- although you might not see any amount of caffeine listed on the label. According to the Agricultural Research Service online report on "Caffeine In Selected Dietary Supplements," there is no requirement to state the amount of caffeine present in a food, beverage, or supplement on the product's label. If caffeine in its pure form is added to a product, however, there is a requirement to add the word "caffeine" to the label's ingredient listing, the report explains.

Dietary supplements -- predominantly weight-loss and sports-nutrition products containing at least one caffeine-containing ingredient -- were chosen for the ARS analysis. Here's what they found:

[Note: According to the Nutrient Data Laboratory, one 8-ounce cup of coffee (240 milliliters) contains about 95 milligrams of caffeine.]

• Of the 53 products analyzed, 27 products provided -- by way of a daily serving defined on the label -- the caffeine equivalent of about one to two cups of coffee.


• Eleven products had caffeine equivalents ranging from two to four cups of coffee.


• Eleven more products had equivalents ranging from four to six cups of coffee.


• Four products provided an amount of caffeine ranging from seven to eight cups of coffee.


• Of the 28 analyzed products that voluntarily listed a caffeine amount on the label, 25 were found to contain caffeine levels within 20% of the label amount.

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