Warnings about yerba mate tea in U.S.

People advised to drink in moderation

People who drink a lot of yerba mate tea may have higher risk of certain cancers, researchers have cautioned. The tea of the moment in the U.S. is attracting fans for its allegedly jitter-free caffeine boost and high antioxidant content.

Lab research suggests some potential health benefits from drinking yerba mate, but studies of lifelong yerba mate drinkers in the tea's native South America suggest the brew increases the risk of some cancers – a fact most marketing campaigns omit.

Yerba mate from the leaves of the Ilex paraguariensis tree, is traditionally brewed and served in a dried out gourd and sipped through a metal straw with a filter on one end to stop drinkers from ending up with a mouthful of leaves.

People talk about yerba mate's clean buzz – a caffeine high without the shakes and ‘crash’ that sometimes follows. It could be because yerba mate contains about 80 milligrams of caffeine per cup – almost twice the amount in black tea but less than half that of coffee, which usually contains 100 to more than 200 milligrams per cup.

But scientist K. Simon Yeung, clinical coordinator and research pharmacist at Memorial Sloan-Kettering Cancer Center in New York City points to a 2003 review of all existing studies on yerba mate, published in the journal Head and Neck, confirmed that people who regularly drink large amounts of the tea – as much as a liter or more each day – had significantly increased risk of cancers of the esophagus, lungs, mouth, pharynx and larynx.

In addition, a study published in the journal Epidemiology in 1994 found that drinking mate regularly increased a person's risk of respiratory or digestive cancers by 60% - leading the authors to conclude that heavy tea consumption could be responsible for as many as 1 in 5 cases of such cancers in southern South America.

In the U.S., he advises, ‘people don't need to stop drinking it, but they do need to know something about it . . . and drink in moderation.’

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