Coffee is one of the favorite beverages of the western world. It also has been rated since 1991 as “possibly carcinogenic to the human urinary bladder” by the WHO’s cancer agency, which will open a week-long review of coffee, mate and “very hot beverages” on Tuesday.
The International Agency for Research on Cancer named a panel of 23 specialists from around the world, including 12 from U.S. institutions, to assess research on coffee over the past quarter-century. The coffee industry says its product is safe and has health benefits.
The session on coffee was announced last June and followed IARC classification of glyphosate, the most widely used weedkiller in the world, as probably carcinogenic to humans in March 2015. Last Oct. 26, IARC listed processed meat as carcinogenic and red meat as probably carcinogenic. Cancer epidemiologist Geoffrey Kabat said last Oct. 30 that coffee is a prime example of how IARC is inclined to find danger everywhere.
The IARC uses a five-point scale to indicate the weight of evidence that an agent can cause cancer, but not the likelihood that cancer will occur; on its website it says it looks at the hazard but not the risk. The rating for coffee is in the middle of the IARC scale. At the top of the scale is “carcinogenic to humans” and at the bottom is “probably not carcinogenic to humans.”
“The IARC gives greater weight to positive results than to negative results, even when the latter are from higher-caliber studies,” wrote Kabat. “Coffee is one of the most widely consumed beverages in the world and one of the most extensively studied components of diet. If we can’t declare coffee to be ‘unlikely to cause cancer,’ what does that say about our ability to assess much more difficult and subtle risks?”
“So which is it — good or bad? The best answer may be for most people the health benefits outweigh the risk,” wrote Dr. Donald Hensrud on a Mayo Clinic website in 2014. “Recent studies have generally found no connection between coffee and an increased risk of cancer or heart disease. In fact, most studies find an association between coffee consumption and decreased overall mortality and possibly cardiovascular mortality, although this may not be true in younger people who drink large amounts of coffee.”
In its 1991 classification, the IARC said “there is limited evidence of carcinogenicity in coffee drinking in the urinary bladder,” and no evidence or inadequate evidence of a relationship with other cancers such as colon, breast, pancreas, ovary “and other body sites.”
Some of the 22 studies examined in the 1991 assessment indicated “a weak positive association” with coffee consumption compared to non-consumption. “Taken as a whole, these data are consistent with a weak positive relationship between coffee consumption and the occurrence of bladder cancer, but the possibility that this is due to bias or confounding cannot be excluded,” said an IARC summary of its 523-page report on coffee, tea and mate.