Carcinogenicity of drinking coffee, mate, and very hot beverages.
www.thelancet.com/oncology Published online June 15, 2016 http:/dx.doi.org/10.1016/S1470 2045(16)30239 X 1 In May, 2016, a Working Group of 23 scientists from ten countries met at the International Agency for Research on Cancer (IARC) in Lyon, France, to evaluate the carcinogenicity of drinking coff ee, mate, and very hot beverages. These assessments will be published in volume 116 of the IARC Monographs. Coffee is one of the world's most widely consumed beverages. It contains many diff erent compounds and its composition varies depending on how it is produced and prepared for drinking. After consumption, caff eine, chlorogenic acids, and other compounds contained in coffee are absorbed and distributed throughout the body. The carcinogenicity of coff ee drinking was last assessed by IARC in 1991. At that time coffee was classified as "possibly carcinogenic to humans" (Group 2B) based on limited evidence of an association with cancer of the urinary bladder from case control studies, and inadequate evidence of carcinogenicity in experimental animals. However, there was also evidence suggesting a lack of carcinogenicity for cancers of the female breast and the large intestine. For this re evaluation, a much larger database of more than 1000 observational and experimental studies was available. In assessing the accumulated epidemiological evidence, the current Working Group gave the greatest weight to well conducted prospective cohort and population based case control studies that controlled adequately for important potential confounders, including tobacco and alcohol consumption. For bladder cancer, there was no consistent evidence of an association with drinking coffee, or of an exposure response gradient from ten cohort studies and several population based case control studies in Europe, the USA, and Japan. In several studies, relative risks were increased in men but were null or decreased in women, consistent with residual confounding from smoking or occupational exposures among men. The Working Group concluded that positive associations reported in some studies could have been due to inadequate control for tobacco smoking, which can be strongly associated with heavy coff ee drinking. By contrast, for endometrial cancer, the fi ve largest cohort studies showed mostly inverse associations with coff ee drinking. These results were supported by the fi ndings of several case control studies and a meta analysis. Inverse associations with coff ee drinking were also observed in cohort and case control studies of liver cancer in Asia, Europe, and North America. A meta analysis of prospective cohort studies estimated that the risk of liver cancer decreases 15% for each 1 cup per day increment. More than 40 cohort and case control studies and a meta analysis including nearly 1 million women consistently indicated either no association or a modest inverse association for cancer of the female breast and coffee drinking. Similarly, numerous cohort and case control studies of cancers of the pancreas and prostate consistently indicated no association between these cancers and coffee drinking. Data were also available for more than 20 other cancers, including lung, colorectal, stomach, oesophageal, oral cavity, ovarian, and brain cancers, and childhood leukaemia. Although the volume of data for some of these cancers was substantial, the Working Group judged the evidence to be inadequate for all of the other cancers reviewed for reasons including inconsistency of findings across studies, inadequate control for potential confounding, potential for measurement error, selection bias or recall bias, or insuffi cient numbers of studies. The combination of evidence suggesting lack of carcinogenicity for cancers of the female breast, pancreas, prostate, uterine endometrium, and liver, with inverse associations for the latter two and inadequate evidence for all the other sites reviewed led to the conclusion that there is inadequate evidence in humans for the carcinogenicity of coff ee drinking. Coffee has been evaluated for carcinogenicity in several long term studies in mice and rats, and has been tested for both tumour promoting and cancer preventing activity in a number of co carcinogenicity studies in rats and hamsters. The Working Group concluded that these studies provided inadequate evidence in experimental animals for the carcinogenicity of coff ee. Coffee drinking exhibited strong antioxidant effects in studies in humans, including in randomised controlled trials. Results for genotoxicity from studies in humans were inconsistent, and coffee did not induce chromosomal damage in rodents. Nonetheless, coffee gave positive results in bacterial mutagenesis assays, but only without metabolic activation. Coff ee promoted apoptosis in human cancer cell lines. Moderate evidence of an association of coffee drinking with reduced risk of colorectal adenoma was noted. Coff ee has also been associated with benefi cial eff ects on liver fi brosis and cirrhosis. Overall coffee drinking was evaluated as unclassifiable as to its carcinogenicity to humans (Group 3) Mate is an infusion made from dried leaves of Ilex paraguariensis. It is consumed mainly in South America and to a lesser extent in the Middle East, Europe, and North America. Mate is traditionally drunk very hot >65degC) but it can also be consumed warm or cold. The carcinogenicity of mate was previously evaluated in 1991, when Carcinogenicity of drinking coff ee, mate, and very hot beverages
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