An exhaustive review of research finds no conclusive evidence of a risk of cancer from drinking coffee, said the International Agency for Research on Cancer in its first look at the hot drink since 1991, when it found a weak link to cancer of the bladder. On the five-point scale used by the WHO agency, the only lower rating than “not classifiable” for coffee is “probably not carcinogenic.”
A panel of 23 experts from around the world, including 12 from U.S. institutions, was appointed by IARC to carry out the review of coffee, mate and very hot beverages. It met for a week in France in late May. On coffee, the experts looked at more than 1,000 studies. There was inadequate evidence of carcinogenicity from coffee in general and inconclusive evidence for 20 types of cancer, said IARC.
“Many epidemiological studies showed that coffee drinking had no carcinogenic effects for cancers of the pancreas, female breast, and prostate, and reduced risks were seen for cancers of the liver and uterine endometrium,” said IARC.
The experts ruled drinking very hot beverages was probably carcinogenic to humans, based on limited evidence linking cancer of the esophagus, the eighth-most common cause of cancer worldwide, and consumption of scaldingly hot beverages. Consumption of mate, an herbal infusion popular in South America, was determined to be “not classifiable” as a cancer risk, the same rating as coffee.
The IARC focuses on evidence of whether an agent is capable of causing cancer, which it calls the hazard. IARC does not measure the likelihood, which it calls the risk, that cancer will result from exposure to the agent. “The distinction between hazard and risk is important,” says IARC. The risk associated with agents given the same classification “may be different, depending on factors such as the type and extent of exposure and the strength of the effect of the agent.”
Critics say the IARC ratings are misleading because they don’t take dosage levels into account. The IARC says exposure levels may change over time.
In October 2015, IARC said processed meat, such as cured or smoked products, is carcinogenic, its strongest categorization. It also said that red meat, which includes raw beef, mutton, horse or goat meat, is probably carcinogenic, the second-strongest rating on its five-point scale.
And in March 2015, IARC said glyphosate, the most widely used weedkiller in the world, is probably carcinogenic to humans. Global use of the herbicide soared following genetic engineering by Monsanto of corn, soybeans, cotton and sugar beets to tolerate the weedkiller.
As with meat, the rating raised howls of protest that continue to reverberate. The European Union is at an impasse over whether to extend approval of use of the weedkiller. Its license expires at the end of the month.
The IARC results were published in the journal Lancet Oncology.