An observer’s perspective: IARC’s evaluation of coffee and very hot beverages

July 5, 2016
Expert comment from Dr Hatzold, ‎an independent consultant in nutrition and scientific affairs that attended IARC’s monograph meeting on drinking coffee, maté, and very hot beverages as an official observer.

The International Agency for Research on Cancer (IARC) is part of the World Health Organization. Its mission is to coordinate and conduct research on the causes of human cancer and the mechanisms of carcinogenesis, and to develop scientific strategies for cancer control. In June, IARC published its review into the scientific evidence related to drinking coffee, maté, and very hot beverages in The Lancet Oncology. Shortly before, over the period of a week, an international Working Group of 23 scientists, convened by IARC, met to evaluate the evidence – over 1000 articles. Official observers, of which I was one, were also in attendance.

This was the first time I had attended an IARC review. I was impressed by the scientific scrutiny demonstrated by the experts as they reviewed each study in detail, identifying individual strengths and shortcomings. The process of the review was clearly set out in advance with scientific rules that helped the experts make objective judgments.

IARC classifies chemicals, common foods and beverages into 5 categories based on the strength of evidence that they may cause cancer. These groups are:

  • Group 1: Carcinogenic to humans
  • Group 2A: Probably carcinogenic to humans
  • Group 2B: Possibly carcinogenic to humans
  • Group 3: Not classifiable as to carcinogenicity
  • Group 4: Probably not carcinogenic

Regarding coffee, the review of the extensive scientific literature found no clear association between coffee intake and cancer at any body site and, in some cases, found some evidence that coffee drinking may actually help reduce occurrence of certain cancers, citing reduced risks for cancers of the liver and uterine endometrium.

Coffee drinking’s classification was therefore revised from “possibly carcinogenic to humans” (Group 2B) previously categorised as such due to limited evidence of an association with cancer of the urinary bladder from case-control studies, to “not classifiable as to its carcinogenicity to humans” (Group 3). It is important to note however, that IARC’s role is to evaluate the science, not assess consumption habits in everyday life and thus does not make any risk assessment, or provide any form of public health advice.

IARC classified drinks consumed at very high temperatures, over 65°C, as Group 2A: “probably carcinogenic to the human oesophagus”. This new classification defined ‘very hot beverages’ as drinks consumed at temperatures significantly hotter than those at which most people can comfortably drink coffee without scalding their mouth and tongue. When IARC assessed evidence for a link between oesophageal cancer and coffee specifically, it found insufficient evidence of an association. Coffee is one of the most widely consumed hot beverages worldwide and it is typically drunk at temperatures well below IARC’s definition of ‘very hot’.

Although IARC has, in recent times, come under criticism for the way in which it communicates its reviews, I feel it is important to note that the agency made every effort to conduct a professional and objective process, and I believe the thorough review and findings presented in The Lancet Oncology demonstrate this. The full monograph is to be published at a later date.


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