12 January - 20 June 2016

Coffee no longer associated with cancer but hot drinks might be

The World Health Organization’s International Agency for Research on Cancer (IRAC) has removed coffee as a carcinogen. For the past twenty-five years coffee has been classified as a possible carcinogen leading to bladder cancer.

The World Health Organization’s International Agency for Research on Cancer (IRAC) has removed coffee as a carcinogen.  For the past twenty-five years coffee has been classified as a possible carcinogen leading to bladder cancer. 

Reporting in the Lancet, the review evaluated the carcinogenicity of drinking coffee, mate and very hot beverages. In 1991 IRAC assessed coffee and classified it as “possible carcinogenic to humans.”  The review states the 1991 classification was based “on limited evidence of 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 more recent evaluation, over 1000 observational and experimental studies were assessed. The Working Group gave more weight to well conducted prospective cohort and population based case control studies which took into account confounding factors such as smoking and alcohol consumption.  Regarding coffee and bladder cancer, the review found, after reviewing 10 cohorts studies and several population based case control studies, no consistent evidence and those that suggested a risk were reported to not have taken adequate “control for tobacco smoking.” For endometrial cancers, the team found that coffee may reduce the risk of liver and uterine cancers. The review notes that some human studies have reported coffee to have a strong antioxidant effect with some reporting coffee to promote apoptosis in human cancer cell lines.

The review also evaluated mate – an infusion made from dried leaves of llex paraguariensis - which is consumed mainly in the Middle East, Europe and North America.  It is traditionally drunk very hot at temperatures of >65oC although the drink can be consumed warm or cold.  In 1991 mate was also classified as “probably carcinogenic to human.”  In this current evaluation the Working Group report studies that show the risk of oesophageal cancer increasing with the quantity of mate consumed.  However the group notes that this association was statistically significant for hot or very hot drinks, with cold mate having no association.  To investigate this further they also analysed other studies which examined drink temperature and oesophageal cancer risk.  They found that drinking very hot tea and very hot beverages similar to very hot mate showed similar results. A rat study found that cold mate reduced the incidence of oesophageal and liver tumours. The Working Group note that “the evidence for very hot beverages and human cancer has strengthened over time with positive association and trend that considered qualitative gradations of temperature.”  New studies indicate that hot water over 65oC can act as a tumour promoter, although the mechanism as to why isn’t clear.  The working group in this current review have therefore classified very hot beverages at above 65oC “as probably carcinogenic to humans “whereas drinking mate that is not very hot was evaluated as not classifiable to its carcinogenicity to humans.”

Another review published in IFT’s Comprehensive Reviews in Food Science and Food Safety has investigated the health effect of drinking coffee and found that that moderate coffee drinking (defined as 3-4 cups per day) essentially has a neutral effect on health, or can be mildly beneficial.  The researchers from Ulster University came to these findings after systematically reviewing 1277 studies from 1970 to date on coffee and health outcomes including mortality, cardiovascular disease, cancer, metabolic health, neurological disorders, gastrointestinal conditions and other miscellaneous health outcomes. 

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