Drinking tea regularly, especially green and black tea, has been associated with a number of health benefits, mainly due to their high content of polyphenols. Polyphenols are plant-based chemicals (including catechins, flavonoids, tannins, etc.) that promote anti-inflammatory properties and improved overall long-term health1.
However, it has been suggested that over-consumption of certain teas can cause health risks. Excess consumption of yerba maté tea has been associated with mouth, throat and esophageal cancers; while excess consumption of green tea and green tea concentrates like matcha (powdered green tea) have been associated with cases liver damage from toxicity.
Today we’re breaking down the evidence for yerba maté and matcha powder and their potential health risks. It’s important to remember that all of the research presented refers to associations, which means there is no proven cause and effect, but there may be a significant relationship between these types of tea and certain health risks.
Esophageal cancer is most strongly associated with yerba maté consumption. One study found that the greatest risk was present in women drinking more than 1L of yerba maté per day2. Research has found that risk for developing cancer significantly increases when drinking yerba maté is associated with increased alcohol and tobacco use. Drinking temperature of the tea may also be important, but this has been harder to prove. Drinking tea that is hot or very hot may increase risk for developing esophageal cancer associated with yerba maté. Other cancers, like cancer of the mouth and throat, have been associated with drinking higher volumes of maté (1.5L and 2L per day, respectively).
The method of how yerba maté may be associated with risk of certain cancers is unknown. One theory is that high temperatures of the tea may be associated with damage to the mouth and throat. Another suggestion is that yerba maté leaves contain poly-aromatic hydrocarbons (PAHs), a compound also found in processed meats that has been associated with increased cancer risk.
This review consisted of studies that involved subjects who were interviewed about their habits around yerba maté consumption. Some things to keep in mind about the research reviewed are subjectivity of responses from participants and concentrations of yerba maté consumed by individuals. Subjects in these studies were asked to remember a) how much maté they drink, and b) how hot their maté typically is. This is important because volume is not always measured or remembered consistently, and because temperature is often very subjective. As well, depending on how each person prepares yerba maté, the concentration of substances in the tea can be very different and may play a role in causing damage to the throat and esophagus.
Yerba maté consumption might increase risk of mouth, throat and esophagus cancers, especially in addition to alcohol and tobacco use. However, the amounts of yerba maté (estimated) that are associated with increased risk are high: At least 1L per day (if not more) – that’s 4 measured cups of yerba maté every day over a prolonged period of time. If you do drink yerba maté consistently, try switching it up between other types of tea and enjoy yerba maté in moderation!
Green Tea & Matcha3
Green tea is often marketed as an herbal supplement aimed at several benefits, including weight loss. This could include tea preparations, extracts or supplements containing green tea.
Excess consumption of green tea (leaves or powder) either alone or in combination with other substances has been associated with some cases of liver damage1,3. Research is still not clear on why this might be the case, however, it seems that consuming high amounts of green tea by concentration or volume, over long periods of time may cause liver damage in some people. The risk may also increase if green tea is consumed on an empty stomach (particularly supplements).
Cases of liver damage with green tea are extremely isolated and most often related to using green tea as an herbal supplement, rather than a normal beverage. Green tea and matcha powder are still safe and even beneficial to consume when enjoyed in moderation. People who have liver conditions should be cautious and consult a doctor about green tea consumption with their condition.
1Hayat K, Iqbal H, Malik U, Bilal U & Mushtaq S. Tea and its consumption: Benefits and risks. Critical Reviews in Food Science and Nutrition 2015;55:7 939-954.
2Loria D, Barrios E & Zanetti R. Cancer and yerba mate consumption: A review of possible associations. Rev Panam Salud Publica/Pan Am J Public Health 2008;25:6 530-539.
3Mazzanti G, Di Sotto A & Vitalone A. Hepatotoxicity of green tea: An update. Arch Toxicol 2015;89 1175-1191.