Does yerba mate cause cancer?
Scientifically, there has never been a study that showed yerba mate to conclusively cause cancer. That’s the simple answer. No one has ever shown yerba mate to cause cancer. However, there is a growing body of research that takes a deeper looking into the mate and cancer situation. As you’ll soon find out from the research video below, there has been a lot of misinformation and confusion around the “mate causing cancer” debate, and today our goal is to shine some light on the situation.
A Fresh Looking into Yerba Mate and Cancer
What is Yerba Mate?
Yerba Mate (pronounced YER-bah MAH-tay) is a shrub native to Argentina, Brazil, Paraguay, and Uruguay. Scientifically named Ilex Paraguariensis, it’s of the Aquifoliaceae family (a Holly plant).
Traditionally, the herb is consumed from a small vessel (also called a “mate” or gourd); a metal straw with a filter (bombilla) is used to draw up the infused mate after warm or cold water has been added. Drunk for thousands of years by the indigenous peoples of South America, the Guaraní, mate has been a staple drink of the continent from untold times. It’s now acclaimed as the National Drink of several South American countries.
Yerba Mate in the United States
Over the past decade there has been an increasing interest in yerba mate, particularly in the associated health benefits of the herb. There has been a great deal of association of yerba mate with weight loss, which has been scientifically proven to help increase metabolism and have anti-obesity effects (Mejia, 2007). However, mate’s ability to increase wellbeing, concentration, provide natural energy, as well as safely increase productivity without the negative side effects of coffee, has become a new focal point of mate in the West.
The term Mateology, coined from the first North American book published on mate, is associated with an erupting philosophy—a way of life—of Mate Drinkers (Materos) who have a deep-rooted relationship with the herb; it’s more than a drink for them, but a way of life. Mate has become a tool of communication and a natural device of sharing and bonding. Never before in Western history have we seen an herb unite North Americas such as mate is beginning to do, especially in the last 3 years (2010—2013).
Pharmacology of Yerba Mate
Though yerba mate has been scientifically studied for over 100 years, it has only been in the last 10-20 years that a renewed, and relatively vigorous, interest into the pharmacology of the herb has begun.
With the work of Elivra de Mejia, Department of Food Science and Human Nutrition, Univ. of Illinois, Urbana, and other notable scientists, we now have a better insight into the chemical makeup of this ancient herb.
We know that mate has a unique array of minerals, antioxidants, vitamins, polyphenols, flavonoids, and acids. It’s becoming generally accepted, through empirical and anecdotal evidence, that mate is significantly more effective than green tea, due to its high concentration of chlorogenic acid, Caffeoyl derivatives, and saponins which have anticancer, anti-inflammatory, lipid-lowering (lower cholesterol), and anti-diabetic properties (regulate glucose levels).
The beginnings Yerba Mate and Cancer Discussion
As Americans, we love our Google. So naturally the term “yerba mate” has over 3M global monthly searches. And the term “yerba mate safety” has over 250K. We’re curious about what we put in our bodies. And rightly so! On the first page of search results, we find several articles which implicate yerba mate in causing cancer of the esophagus or other parts of the upper aerodigestive tract: mouth, oral cavities, throat, etc.
The primary article, in Los Angeles Times, is “Yerba mate tea: Drink in moderation,” by Elena Conis. It states:
…Scientists disagree about the bottom line on yerba mate, says K. Simon Yeung, clinical coordinator and research pharmacist at Memorial Sloan-Kettering Cancer Center in New York City. The tea does contain a long list of vitamins, minerals and antioxidants, including B vitamins and vitamin C; manganese, potassium and zinc; and the beneficial plant compounds quercetin, theobromine and theophylline.
One study of roughly 1,000 adults in Uruguay, published in the journal Cancer Epidemiology Biomarkers & Prevention in 1996, found the risk of lung cancer to be 60% higher among mate drinkers. Another Uruguayan study, published in the same journal in 2003, found that in a group of about 800 adults, mate drinking tripled the risk of esophageal cancer.
Though Conis did not explicitly state the researchers involved in the studies, her references stem from the work of Eduardo De Stefani. Conis was referring to his 1996 publication “Mate drinking and risk of lung cancer in males: a case-control study from Uruguay.”
That study, as well as several subsequent studies by De Stefani and his team, encompass nearly 15 years (1990—2004) of case study investigations looking into the connection between mate and cancer.
I will be referring to the cumulative body of De Stefani’s work moving forward, in particular with his recent publication “Maté Consumption and Risk of Cancer: a Multi-site Case-Control Study in Uruguay” (Asian Pacific Journal of Cancer Prevention, 2011), where he incorporates his previous studies.
Eduardo De Stefani’s Cancer Research
Between the years 1990—2004 De Stefani and his team of social workers in Montevideo, Uruguay, studied 13,201 participants (8,875 cases and 4,326 controls), from four major public hospitals. De Stefani used a statistical measurement called an OR (odds ratio) to evaluate the odds of someone getting cancer as a result of drinking mate compared with others who did not consume mate or had consumed it in a particular way.
Using interviews and questionnaires, patients were asked about their age, sex, education, income, weight, height, history with alcohol, cigarettes, yerba mate consumption (amount, hot, cold), etc.
From this retrospectively gathered information, De Stefani suggested that due to chemicals known as PAHs (Polycyclic Aromatic Hydrocarbons), yerba mate may be responsible for an increase in certain cancers (we’ll discuss PAHs in more detail later).
Flaws, Biases, and “Adjustments” of De Stefani’s Cancer Research
However, what Elena Conis irresponsibly and carelessly omitted from her article in the Los Angeles Times, “Yerba mate tea: Drink in moderation,” were the limitations of De Stefani’s research. Which we’ll discuss in 4 principal segments: Socioeconomic status, Diet, Currently Sick Patients, and Subjective responses to questions.
With any given epidemiological and scientific study, there are limitations which invariably confound (or confuse) the results of the experiments. Scientists use the term “adjusting” in an attempt to compensate for these inherent biases and limitations, but there is only so much adjusting that could be done.
From the start, it should be stated that there has NEVER been a population-based, or any scientific study, that has conclusively proven yerba mate to cause cancer. Such a basis is critical to begin the dissection of De Stefani’s work.
Currently Sick Patients
It is important to understand that all of the participants in these studies were already sick with a slew of diseases: skin diseases, blood disorders, eye disorders, disease of the nose, goiter, disease of the mouth; various cancers of the mouth, colon, esophagus, prostate, bladder, kidney, etc.
Many of these patients consumed alcohol and smoked black tobacco as well, which may have been the primary contributors in these aforementioned diseases. David Goldenberg, MD, states in his paper “The Beverage Maté: A Risk Factor for Cancer of the Head and Neck,” (HEAD & NECK, July 2003):
The main problem in evaluating the effect of maté consumption as a carcinogenic agent is the difficulty in obtaining the appropriate control of confounding risk factors such as alcohol and tobacco use.
Dora Loria, in the paper “Cancer and yerba mate consumption: a review of possible associations,” (Rev Panam Salud Publica, 2009) adds to the discussion:
Choosing to use hospitalized controls could be a cause of confounding in the results. From a methodological point of view, it would have been more appropriate to use subjects from the general population in the control groups…
De Stefani admits that “perhaps selection bias and recall bias are the major limitations. Since both groups were drawn from low socioeconomic strata…”
To speak bluntly, the participants in the study were poor. With abject-poverty comes poor diet and nutrition, as well as poor education and and lack of full comprehension of the questions being asked. There are literally incalculable and immeasurable variables that participate in acquiring a disease, not to mention the genetic predispositions that cannot be well quantified nor comprehensively controlled in the studies. Such information is out of the scope of the researcher’s parameters.
Participants were asked if they drunk mate warm or hot. The hypothesis of hot mate being the culprit of cancer through thermal carcinogenesis, has been widely accepted within the community of researchers involved in the matter.
The fact is that most of the participants could not truly gauge what “warm” or “hot” (similar experiments used “warm,” “hot,” and “very hot”) was, since these terms are relative to the drinker, thus resulting in highly subjective responses. One man’s “warm” may be another woman’s “hot.”
I know from 3 years of personal experience, living in Argentina and Uruguay, that many mate drinkers consume it with scolding hot temperatures, exceeding 190oF, which is very normal to many drinkers of the Southern Cone.
Loria (2009), referring to a Brazilian study (Silva de Barros S, 2000), stated that “The temperature of the beverage was, in general, self-evaluated, defined subjectively as “warm,” “hot,” and “very hot,” and these categories presented only limited correlation with thermometer readings.”
From various studies on the dangers of drinking ANY hot beverage —well documented in Japan, China, and Iran (Ghadirian P. Thermal irritation and esophageal cancer in Northeastern Iran, Cancer, 1987; Wang JM, Diet habits, alcohol drinking tobacco smoking, green tea drinking…Eur J Gastroenterol Hepatol, 2002), we know that the substance alone isn’t to blame, but the procedure of how it’s prepared—with very hot temperatures. This inflammation of the throat lining causes esophagitis, a precursor to esophageal cancer.
In a similar case study conducted in Brazil, researchers admitted that the evaluation of the role of temperature may have been biased because of the unclear classification of beverage temperature (Goldenberg, 2003).
A consequence of poverty is poor diet. It is firmly established that a high intake of fresh fruits and vegetables are responsible for attenuating the chances of developing cancers or any disease of the body.
It is highly likely that the lack of vegetables coupled with the high intake of charred meats, prepared in the traditional BBQ (asado) methods of South America, play critical roles in the development of the already-diseased patients in the study.
15 polycyclic aromatic hydrocarbons (PAHs), known carcinogens, have been identified in 11 brands of mate (Zuin, 2005); however, these chemicals are found in all roasted (BBQ) foods, green tea, tobacco smoke, and common soap products.
Some researchers believe that the high intake of meat from the participants played a role in disease: Referring to a Brazilian study, Loria (2009) discussed the PAHs in association with BBQ meats:
Concentrations [PAHs] varied according to cigarette and mate consumption with the exposure to asados (or open fire used for barbecuing meat). This observation led the authors to conclude that the population could be exposed to certain levels of PAHs through tobacco smoking, as well as mate drinking and inhaling asado smoke.
Subjective Responses to Questions
Participants were asked to recall past actions, which were used as data points to draw conclusions by De Sefani and his team. The problem with this is multifaceted. As previously mentioned as per the temperature of the mate drunk, the room for error is incredible. Moreover, as of yet, there remains no standard method to properly gauge the exact amount of mate consumed by each participant, as each drinker consumes mate in various size gourds, cups, tea bags, etc.
And to expect the (very sick) participants to recall the exact amount of mate consumed over any duration of time, in this case, years, is unrealistic. Further standardization of measurements and temperatures need to be undertaken for such epidemiological studies to carry more validity.
Validity of Cancer and Mate Possible Association
Hot Mate with Tobacco and Alcohol Usage
Notwithstanding the obvious flaws and limitations of De Stefani’s research, which from all subsequent studies linking mate to esophageal cancer stem, a connection between the consumption of (hot?) yerba mate coupled with smoking and alcohol, cannot be ignored.
De Sefani, as well as other isolated case studies in South America, have consistently linked higher incidences of cancer with smokers and drinkers who also drunk hot mate.
- “Most studies in humans strongly suggested that maté acts as carcinogen due to the high temperature of the ingested liquid… Cancers [esophageal, bladder and lung] were strongly positively associated with hot maté drinking. ” (De Stefani, 2011)
- “The synergistic action between mate, alcohol, and tobacco was a clear result in several studies.” (Loria, 2009.)
- Referring to a Brazilian study (Putz, Int J Cancer, 2002), “the authors postulated that the presence of these mutational differences could be explained, as least partially, by the presence of chronic inflammatory process due to mucosal irritation caused by very hot mate commonly drunk in this area.” (Loria, 2009)
- Rolon (Cancer Epidemiol Biomarkers, 1995) “found that those who drunk cold maté did not have an increased risk of esophageal cancer, whereas drinkers of very hot maté did have an increased risk of esophageal cancer, even after adjustment for the effects of alcohol and tobacco.” (Goldenberg, 2003)
- “It has been proposed that maté may act as a solvent for the chemical carcinogens found in tobacco or that phenolic compounds contained in maté may act as cancer promoters.” (Goldenberg, 2003)
It is clear that more research needs to be done in this area, but there does seem to be a connection between mate (which is mostly drunk very hot in South America) and the usage of tobacco and alcohol, combined with the high intake of charred meat and BBQ smoke (which contains PAHs).
I hypothesize that the powerful antioxidant compounds found in mate act to increase the solubility of already-present carcinogens found in the body from alcohol and tobacco, as mate does in like manner with increasing the solubility of health-promoting nutrients and vitamins, with the powerful aid of saponins and chlorogenic acid.
Perhaps the mate is attempting to rid the body of these toxins, and as the drinker continues to consume alcohol and smoke in excess, the mate never fully gets a chance to do its job. I speculate this may have something to do with mate being used as a temperance drink at the turn of the 20th century. Even today, we are able to find anecdotal evidence of mate’s ability to curb the desire of alcohol consumption and replace tobacco.
The body is attempting to alkalize and return to homeostasis, but with the abundance of toxins bombarding the system, subsequently building up due to the increased solubility factors of the mate, they have no effective way to leave the body; this may result in oxidative stress, which in turn, may be responsible for these correlations found with mate and alcohol and tobacco consumers. And the fact that most of this mate is being consumed hot, leading to the inflammation of the mucosa lining of the throat and lungs, the factors continue to compound in favor of cancer initiation.
The PAHs identified in mate perhaps now become more of a threat in such a toxic and susceptible environment. Though, it has been widely hypothesized that the PAHs in mate result from improper drying methods and storing, as well as the leaves being smoked or burned over direct flames.
Based upon these studies, it is suggested to consume mate below180oF, preferably closer to the 155-170ºF range, as well as limiting tobacco and alcohol consumption, effectively assuaging potential associated risks.
Discussion and Conclusion
Is Yerba Mate Safe to Drink?
Yerba mate has been well established as a powerhouse of health and nutrition. With antioxidants significantly higher in concentration than green tea, in addition to the significant amounts of chlorogenic acid and saponins unique to mate (Mejia, 2007), yerba mate has shown to be an effective drink (when consumed with the right temperature) of health, both socially and scientifically.
Several studies have actually shown mate to destroy cancer cells (Bixby, et al, 2005). In 2011, in a study conducted by Elivra de Mejia, mate was shown to destroy colon cancer cells in vitro.
“Several studies have been conducted on the anticancer properties of Mate tea and comparisons have been made with other teas such as green tea, believed to have high anticancer potential. Mate was shown to possess the highest cytotoxicity against human liver cancer cells compared to green tea.” (Yamamoto, 1997; Ramirez- Mares, 2004).
- “[Mate] has been shown that oral cancer cells can be completely inhibited by treating them with 375 μg of Mate extract/mL.” (Mejia, 2007).
- “In 1991, the International Agency for Research of Cancer (IARC) evaluated the carcinogenic risk of mate and concluded that there is limited evidence for carcinogenicity of hot mate in humans.”(Loria, 2009).
- Yerba Mate has been placed on the U.S. Food and Drug Association’s GRAS list as an items that is “Generally Recognized as Safe to Consume.”
- Yerba mate has been historically consumed for thousands of years by the Guaraní peoples of South America, and revered for its healing and naturally energizing effects. They prayed to the God of Mate and called it the “Drink of the Gods.”
Elvira de Mejia (2007), the foremost mate scientist, taking into consideration the cancer studies as well as the wide array of health benefits of yerba mate, presents a concluding thought:
Yerba mate has been consumed for centuries but it has only been scientifically studied in the last 2 decades. The growing worldwide interest in Mate has made it paramount that research on this herbal tea continues, as it has shown extraordinary possibilities not only as a consumer beverage but also in the nutraceutical industry. In regard to carcinogenesis, the most recent information suggests that the association between Mate consumption and the occurrence of cancer may not be due to the raw material itself but to contaminants that may be present in processed Mate. The high temperature at which Mate tea is consumed may also play a role. Therefore, postharvest technologies need to be improved—especially the drying process needs to be optimized to completely eliminate contaminants. Additionally, good quality control, including [thorough] analytical testing becomes imperative to insure its safety.
Suggested Safety Measures when Consuming Mate
- Know where and how your mate is processed. Taking into account these studies discussed, particularly with the understanding that PAH levels can be controlled by limiting flame contact to leaves during postharvet, and removing contaminants from the storage facilities, it would be wise to select the cleanest, non-smoked, organic yerba mate available to you. Being able to ask the company owner such questions as to the quality control of the mate has never been more critical.
- Don’t drink your mate very hot. Properly gauge the water temperature used to drink mate. Never drink boiling water. A suggested temperature of around 165ºF is recommended.
- Understand the building correlation between alcohol and tobacco consumption with yerba mate. If you do smoke and drink, then take extra precaution not to drink very hot mate.
- Mate may work best in addition to a healthy diet and lifestyle. Eating plenty of fresh fruits and vegetables, combined with sufficient exercise and relaxation, may help offset the chances of developing disease and boost mate’s ability to reduce oxidative stress (proliferation of free radicals).
Updates and Recent Studies
As of March 2018, from BMC Cancer, “Comparative esophageal cancer risk assessment of hot beverage consumption (coffee, mate, and tea): the margin of exposure of PAH vs very hot temperatures” by Okaru, Gonzalez de Mejia, et al.
Below are citations from the study, that further corroborate that there is no evidence to associate yerba mate with cancer, apart from drinking “very hot water” (65ºC | 150ºF), despite the medium of herbs (yerba mate, tea, coffee etc). The most important take away here is the International Agency for Research on Cancer (IARC), which has formerly associated yerba mate with cancer as of 1991, has, as of 2016, reclassified yerba mate from a potential carcinogen to a group of “very hot beverages at above 65ºC drinking” that may lead to cancer, not due to the material being consumed, but the temperature at which it’s consumed.
This is quite important to clearly grasp: it’s not the yerba mate, it’s the temperature that may be dangerous, which “may start at [149ºF]”.
The temperature effect but not PAH exposure may pose an esophageal cancer risk. Consumer education on risks associated with consumption of ‘very hot’ beverages and policy measures to threshold serving temperatures should be discussed.
Considering that there is very little evidence that [yerba mate] contain high amounts of PAH, it has become the prevailing hypothesis that the risk might not be inherent to the natural compounds contained in mate, or to compounds produced during processing, but rather due to temperature effect.
…very hot drinking temperatures are probably causally related to esophageal cancer whereas low temperature mate is not.
…the assumption [is] implausible that PAH and temperature may act synergistically.
…a large pooled analysis was conducted that reported estimates of association between mate drinking and esophageal cancer stratifying by temperature and showed little evidence of association when mate was consumed warm [below 149ºF degrees], regardless of the amount consumed, thus supporting a role of very hot temperatures and not mate per se.
The author of this report, David Askaripour (aka “Dave Mate”) is the founder of an International Yerba Mate Community (since 2011), Circle of Drink, and a provider of organic yerba mate and yerba mate products at circleofdrink.com. There was an unavoidable bias towards the consumption of mate; however, the author, before being associated with selling mate products, had lived in Argentina for over 2 years studying the herb. In total, the author has close to 5 years experience of personal daily consumption (>1L/day), interviews of mate consumers, dozens of published videos discussing the health effects of mate (youtube.com/circleofdrink), and has published the first U.S. based yerba mate book, Mateology (2013) (circleofdrink.com/mateology).
- Elvira de Mejía, “Yerba Mate Tea (ilex Paraguariensis): A Comprehensive Review on Chemistry, Health Implications, and Technological Considerations.” Journal of Food Science 72, no.9 (2007): R138–R151.
- Goldenberg D, “The Beverage Maté: A Risk Factor for Cancer of the Head and Neck.” Head Neck 25, no. 7 (2003): 595–601.
- Elena Conis, “Yerba Mate tea: Drink in Moderation.” Los Angeles Times, 2009.
- Eduardo de DeStefani, “Maté Consumption and Risk of Cancer: a multi-site Case-constrol Study in Uruguay.” Asian Pacific Journal of Cancer Prevention 12, no.4 (2011):1089-93.
- Dora Loria, “Cancer and yerba mate consumption: a review of possible associations.” Rev Panam Salud Publica 25, no.6 (2009):530-9.
- Ghadirian P, “Thermal irritation and esophageal cancer in northern Iran.” Cancer 60, no.8 (1987):1909-14.
- Wang JM, “Diet habits, alcohol drinking, tobacco smoking, green tea drinking, and the risk of esophageal squamous cell carcinoma in the Chinese population.” Eur J Gastroenterol Hepatol 19, no.2 (2007):171-6.
- Zunin, “Stir bar sorptive extraction and high-performance liquid chromatography-fluorescence detection for the determination of polycyclic aromatic hydrocarbons in Mate teas.” J Chromatogr A. 1091, no. 1–2 (2005):2-10.
- Bixby M.,“Ilex paraguariensis extracts are potent inhibitors of nitrosative stress: a comparative study with green tea and wines using a protein nitration model and mammalian cell cytotoxicity.” Life Sci. 77, no.3 (2005):345-58.
- Takehiko Yamamoto, “Chemistry and Applications of Green Tea,” New York: CRC Press. p61–73.
- FDA’s GRAS List, “Botanicals Generally Recognized As Safe,” FDA, http://www.ars-grin.gov/duke/syllabus/gras.htm (accessed July 1, 2012).
Statements have not been approved by FDA
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