Yerba mate is an herbal tea that has been touted for a number of health benefits but has also been linked to an elevated risk of cancer. Commonly used in South America, the tea has been hitting the shelves of health food stores in the United States and other countries where it is marketed as a supplement to improve energy levels and assist in weight loss.
Despite having anti-oxidant properties, population studies have demonstrated increased rates of esophageal, head and neck, bladder, and some other cancers among users of the tea. We will look at these properties, as well as cell, animal, and epidemiological studies to date.
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What Is Yerba Mate Tea?
Yerba mate is a tea made of dried leaves from the plant Ilex paraguariensis. Consumed predominantly in South America in the past, it is now widely available in the United States. The leaves are dried with a heat source and stored, then steeped with hot water (usually very hot) to make tea.
In addition to a beverage, it is sold as a supplement in pharmacies and health food stores. There have been many claims made, with most of these asserting that the tea can help raise energy levels and assist with weight loss.
The tea goes by many different names including Cimmaron, St. Bartholomews’s tea, and more.
Mate: Classification as a Carcinogen
In 1991, the International Agency for Research on Cancer (IARC) classified hot mate drinking as a Group 2A carcinogen, meaning that the tea was “probably carcinogenic to humans.” This was based on studies showing an increased risk of esophageal cancer, though the relationship was only significant for those who drank their mate hot or very hot.
Subsequent analysis (after 1991) found that not only mate—but other beverages—appeared to be carcinogenic when consumed hot or very hot. In addition, animal studies found that hot water-induced esophageal tumors in nitrosamine treated rodents, but cold mate reduced the incidence of these tumors.
On the basis of these considerations and on the totality of the evidence, drinking very hot beverages at above 65°C was classified as “probably carcinogenic to humans” (Group 2A) in 2016. This evaluation of very hot beverages includes drinking of very hot mate. Drinking mate that is not very hot was reclassified as “not classifiable as to its carcinogenicity to humans” (Group 3).
Yerba Mate and Cancer
Yerba mate contains components good and bad that may be associated with either an increased or reduced risk of developing cancer. Some components may actually be good or bad depending on the individual person. For example, Yerba mate contains caffeine which may be good if you experience headaches or need a pick-me-up, but bad if you are sensitive to caffeine and experience palpitations and other symptoms.
Potentially Beneficial Components
On the positive side, Yerba mate contains some nutrients that may be beneficial for health. For example, mate contains phytonutrients such as polyphenols that act as free radical scavengers.
Free radicals are unstable molecules that are produced during metabolism or due to exposure to toxins that can, in seeking out electrons to become stable, cause molecular damage such as changes to DNA.
Researchers wondered whether these phytonutrients may reduce oxidative damage in cells, and hence, help reduce the DNA damage that can lead to cancer.
Using mice that were regularly fed Yerba mate, and comparing that group with non-mate consumers, they evaluated DNA in both groups after exposure to a chemical that causes DNA damage. The mice who consumed Yerba mate had less damage (fewer breaks in DNA), as well as an improvement in DNA repair.
Of course, since this experiment was done on rodents, it doesn’t necessarily translate to humans.
Potentially Dangerous Components
Yerba mate tea also contains potentially dangerous components. One of these, polycyclic aromatic hydrocarbons (PAHs) are a group of over 100 compounds. One PAH, in particular, bento[a]pyrene is considered a group I carcinogen (the category of substances most likely to cause cancer) or “carcinogenic to humans.”
Several other PAHs, some of which are found in mate, have been labeled as “probably carcinogenic” by the IARC. Of note, is that it is PAHs (along with heterocyclic amines) that are the compounds produced when grilling meats that are thought to increase cancer risk.
A 2019 study noted that when the leaves of Ilex paraguariensis are dried by smoking (a very common method), the products produced may have high amounts of PAHs. In a sampling of 10 specimens, it was found that nearly all had high mass fractions of these chemicals. That said, since the compounds are hydrophobic (avoid water), they may not readily enter the liquid state of the brewed tea. The researchers recommended further studies to determine if PAHs in Yerba mate are of concern or not.
A different study performed in 2018 concluded that it was likely the temperature effect of hot Yerba mate tea rather than the presence of PAHs that was of most concern, at least with regard to the risk of esophageal cancer.
Yet other researchers have postulated that both high temperatures and PAHs may be a problem and that high temperatures may actually increase the carcinogenicity of PAHs in mate.
The temperature could damage the sensitive lining (mucosa) of the esophagus so that metabolic reactions or direct damage to the esophagus from mate would be more likely to occur.
Overall, the jury is still out on whether or not we should be concerned about the amount of PAHs in yerba mate tea.
Research on Yerba Mate
Research looking at how a substance may affect humans when ingested can be gathered from cell studies in the lab and animal studies. Since it would be unethical to actually test a substance on humans directly, researchers look at population studies.
For example, do people who drink yerba mate appear to have a higher or lower risk of any types of cancer? In regions where drinking mate is common, are there increased or decreased risks of cancer relative to other regions?
Several cell studies have evaluated the effect (either positive or negative) of yerba mate both on normal human cells and on human cancer cells.
Potentially Beneficial Effects
An older study tested the hypothesis that components found in Yerba mate (caffeolquinic acids) might have anti-inflammatory and anti-cancer properties.
In the lab, an isolate of these acids from Yerba mate reduced inflammation of a type of immune cell that led to increased cell death (apoptosis) of human colon cancer cells. These results suggested that yerba mate contained potential anti-cancer agents (and might also help with diseases caused by inflammation), but it’s difficult to know if results obtained in a lab would have any relationship to what might be seen in the human body.
In another study with human cancer cells (colon, esophageal, and bladder) and regular cells, the main components of mate in high concentrations decreased the viability of cancer cells. When they looked at concentrations of these substances at normal dietary concentrations, however, no effect was seen.
Yet another study looking at the components of Yerba mate (primarily caffeoylquinic acids), found pretreatment of cells with these components reduced oxidative stress caused by tumor necrosis factor-alpha.
While these studies are encouraging, none can tell us what might be expected when yerba mate enters the much more complex system of the human body.
One study in rats treated with a concentrate of Yerba mate had a positive effect, but not with regard to cancer. In this study, rats were treated with an extract of Yerba mate prior to exposing their hearts to low oxygen (ischemia) such as would be seen with a heart attack.
The extract of yerba mate appeared to reduce the heart damage caused by lack of oxygen and then reperfusion.
There is potential that the tea could help with oxidative damage caused by carcinogens in humans as well, yet it’s well known that animal studies don’t necessarily translate to humans.
Sadly, what has been seen in cell studies and animal studies doesn’t translate well to epidemiological studies in people, where the consumption of yerba mate tea (at least high and prolonged use) has been linked to an increased risk of cancers of the:
- Head and neck
As is the case with so many cancers, the ultimate cause is usually multifactorial, meaning that several factors usually work together to either increase or decrease risk. For example, with esophageal cancer, heavy alcohol use or smoking combined with yerba mate tea appears to increase the risk by a factor of three to seven.
We will look at some of the individual studies looking at various cancers to appreciate the relative magnitude of risk with different cancers.
Overall Cancer Risk
A 2018 review of 569 studies studies to date looked at the association of yerba mate with a number of different cancers. The study found an association between drinking Yerba mate tea and cancers of the upper airway and upper digestive tract including:
- Oral cancer
- Pharyngeal cancer
- Esophageal cancer
- Laryngeal cancer
Unlike some studies that appear to implicate temperature, no differences were found between those who drank the tea cold or warm and those who drank their tea hot or very hot.
Drinking larger amounts of the tea was linked to a greater risk, with those consuming one liter or more daily having 1.72 times the risk of those who drank less than one liter daily.
Several studies have looked at the possible association between drinking Yerba mate and the incidence of esophageal cancer.
Since drinking liquids at high temperatures is a risk factor for these cancers, it can be challenging to separate out the role of yerba mate specifically and the drinking of hot beverages alone when assessing risk.
For example, a 2015 study found that hot beverage or food consumption was associated with a significantly increased risk of developing esophageal cancer, especially in countries in South America and Asia.
It’s also important to note that there are two primary types of esophageal cancer that have different risk factors:
- Squamous cell carcinoma
Squamous cell carcinoma of the esophagus is of greatest concern and has other risk factors including:
- Heavy alcohol use
- Environmental exposures such as to polycyclic aromatic hydrocarbons
Genetic factors can also play a role. Adenocarcinoma of the esophagus has different risk factors, with gastroesophageal reflux disease (GERD) being of the greatest concern.
A review of studies found that consumption of yerba mate tea was associated with a risk of esophageal squamous cell carcinoma that was 2.57 times that of non-drinkers of the tea. Heavy drinkers of mate were also more likely to develop cancer than light drinkers of the tea.
Studies suggest that people who consume yerba mate (at least in South America) have more than twice the risk of developing squamous cell carcinoma of the esophagus.
In a study in Uruguay looking at a number of foods and prostate cancer risk, mate consumption was associated with almost a doubling (OR of 1.96) in prostate cancer risk.
In an older study done in Uruguay, heavy drinkers of Yerba mate were found to have 1.6 times the risk of developing lung cancer when compared with light drinkers of the tea. Lending further support that this was a true increase was that risk increased with the duration of use (referred to as a dose-response pattern).
Heavy drinkers of mate were more likely to be diagnosed with small cell lung cancer (the less common form of the disease, responsible for around 20% of lung cancers), but not lung adenocarcinoma. Small cell lung cancer is the type of lung cancer most strongly linked with smoking (similar to what is seen with esophageal cancers), but the researchers controlled for this variable in the study.
Head and Neck Cancers
A review of studies found that drinking Yerba mate tea was associated with a risk of oral and oropharyngeal cancer slightly more than twice as high of that for non-drinkers of the tea, though temperature was not controlled for in these studies.
Based on the review, it was felt that the population attributable risk for mate drinking (number of total cases of oral and oropharyngeal cancer that were directly “caused” by drinking mate) was 16%.
In a relatively small study, researchers looked at the incidence of bladder cancer in people who had consumed mate in the distant past (20 to 40 years prior). For people who had smoked (ever smokers), the risk of bladder cancer was almost four times higher in mate users than in non-mate drinkers.
No increase in bladder cancer was seen in lifelong non-smokers, even those who consumed large amounts of mate. The particular type of Yerba mate may also be important. The increase in risk was seen in those who consumed the strain mate con bombilla but not mate cocido.
Mate may increase bladder cancer risk in people who smoke or smoked in the past.
Side Effects and Contraindications
Like almost any beverage and supplement, there are potential side effects related to drinking yerba mate as well as reasons why some people should avoid it completely (contraindications).
Yerba mate contains caffeine which can have a stimulant effect. Some people can experience:
- Rapid heart rate
- Digestive upset
In large amounts (more than 12 cups daily), people may experience:
- Ringing in their ears
Some children who have been born to mothers who consumed Yerba mate tea have experienced withdrawal, similar to caffeine withdrawal.
While adverse effects are uncommon, at least one case of severe hepatitis (liver inflammation) and subsequent liver failure has occurred.
Cautions and Contraindications
Due to the stimulant effects of yerba mate tea, caution should be taken (or the tea avoided altogether) in people who have:
- Heart disease
- Heart arrhythmias
- High blood pressure
People who have inflammatory bowel syndrome should likewise be careful, as yerba mate tea may increase diarrhea.
For people who have diabetes, especially type I diabetes, blood sugars should be closely monitored for changes. Yerba mate can also increase pressure inside the eye (due to caffeine) and should be avoided in people with glaucoma.
Caffeine has been noted to result in slow clotting for some people, and the tea should be used with caution (and only under medical advice) in people who have bleeding disorders or are on medications that can increase or decrease clotting.
Due to its antioxidant effects, yerba mate tea should not be consumed by people undergoing chemotherapy.
Yerba mate tea may interact with medications and drugs that have stimulant effects such as:
- Amphetamines (eg. Adderal)
- Ephedrine (in many cold and cough preparations)
Pregnancy and Breastfeeding
Yerba mate tea is considered possibly unsafe in pregnancy, as consuming over 300 mg of caffeine daily (around 6 cups of mate tea) is associated with an increased risk of miscarriage and preterm labor. It is also considered possibly unsafe during breastfeeding as it’s not known if components of the tea enter breast milk or not.
If you decide to consume yerba mate tea, consider reducing other risk factors for cancer. Some measures that may reduce risk include:
- Stopping smoking
- Avoiding excess alcohol intake
- Limiting intake of grilled meats (a source of PAHs)
- Reducing your risk for human papillomavirus infection (HPV)
- Eating a wide range of vegetables and fruits daily
- Minimizing your intake of red and processed meat
A Word From Verywell
Despite having some properties and actions in cell cultures that suggest a lower risk of cancer, drinking yerba mate tea is associated with an increased risk of developing several types of cancer, especially esophageal cancer.
If you do enjoy the tea, consider looking at other risk factors that you can control, and avoid overly hot tea. Keep up to date on the latest research on the tea as well as new findings that may emerge. Certainly, there are risks related to many of the foods we eat and activities in which we take part. But being aware of potential risks and minimizing our exposure is an important part of being our own health advocates in a world in which one in two men and one in three women are expected to develop cancer during their lifetime.