In June 2016, the International Agency for Research on Cancer (IARC) reported on their evaluation of studies of coffee, maté (a caffeine-rich tea drink made from steeping yerba mate [Ilex paraguariensis] ground-up leaves in hot water), and other hot beverages and their relationship to esophageal cancer. The 23 scientists that produced the study published the findings in the Lancet Oncology; the detailed findings will be published in volume 116 of the IARC monographs.
Drinking coffee does not cause cancer
The working group found no conclusive evidence that drinking coffee or maté causes cancer. However, the scientists did conclude from their studies that drinking very hot beverages of almost any type probably causes cancer of the esophagus in humans. Consequently, their results suggest that drinking very hot beverages is one possible cause of esophageal cancer. They concluded that drinking very hot beverages should be classified as probably carcinogenic to humans. The investigators were very clear that the evidence suggested that "very hot" temperatures were responsible for this probable carcinogenic effect. The scientists were specific about the temperature required to cause this effect; it was determined that beverage temperature of 65 C (or about 149 degrees Fahrenheit) or above was required for the effect. Experiments involving animals showed "limited evidence" that even very hot water was responsible for the carcinogenicity. Furthermore, the majority of esophageal cancers that occur in Asia, South America, and East Africa may be linked to the consumption of drinking very hot beverages since drinking them very hot temperatures (about 70 C) is a common practice. However, in the U.S. and Europe, coffee, tea, hot chocolate, and other beverages are commonly consumed at temperatures below 65 C. The 65 C temperature is hot enough to cause burns on the tongue.
In their report, they dropped coffee from the list of possible carcinogens. This was a change from their previous 1991 classification that linked coffee drinking to bladder cancer. The researchers came to this decision after better studies were completed years later and showed no clear relationship to drinking coffee and bladder cancer development. In addition, the scientists suggested that drinking maté that is not very hot or cold (below 65 C) was not classifiable as to its carcinogenicity in humans.
Prevalence of esophageal cancer
While many scientists are awaiting the detailed findings that are yet to be published, it is significant that the World Health Organization and others consider these findings provide enough evidence to conclude that very hot fluids (65 C and above), no matter what the composition, transfer heat to the esophagus and thus provide a cause for the development of esophageal cancer. Esophageal cancer causes about 5% of cancer deaths worldwide, or about 400,000 deaths related to esophageal cancer.
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Dana, L., et al. "Carcinogenicity of drinking coffee, mate, and very hot beverages." Lancet Oncology June 15, 2016. <http://www.thelancet.com/journals/lanonc/article/PIIS1470-2045%2816%2930239-X/fulltext>.