Green Light for Coffee

"Last year the IARC said that bacon is carcinogenic, but it became clear that when eaten in moderation it is not very risky. In the case of very hot drinks, the IARC concludes they are probably hazardous, but can't say how big the risk might be."
"This may be interesting science, but makes it difficult to construct a sensible response."
David Spiegelhalter, professor, Public Understanding of Risk, University of Cambridge, UK 

A cup of coffee served at a coffee shop in Caracas, Venezuela, February 26, 2015.

Reuters/Jorge Silva/File Photo

The International Agency for Research on Cancer (IARC) is comprised of 23 experts meant to bring their scientific expertise to officially proclaim on behalf of the World Health Organization their collective finding on whether carcinogens exist as a threat to human beings in products we take for granted. Take the morning/afternoon/evening beverage favoured the world over, hot or cold, strong or weak, dark-roasted or light, organic and/or fair-trade (or not) -- the latest finding has been to downgrade the risk of cancer derived from coffee.

Following what the WHO understands to have been an exhaustive review of the data on the part of their agency, the word is now a reversal of their earlier finding; no conclusive evidence of harm. Previously the IARC had issued the finding that drinking "very hot beverages", whose temperatures exceed 65C is a likely cause of cancer of the esophagus, one of the very most deadliest and feared of cancers. That caution remains.

Yet while this latest review saw "no conclusive evidence for a carcinogenic effect" of drinking coffee, the review did point to studies that show coffee may in fact reduce the risk of developing certain types of cancer. "(This) does not show that coffee is certainly safe ... but there is less reason for concern today than there was before", said Dana Loomis, deputy head of IARC's Monograph classification department.

But there is a caution where epidemiological studies out of China, Iran, Turkey and South America indicate that beverages such as tea, mate or coffee traditionally served so hot it can burn the tongue, may lead to esophageal cancer. Studies out of this hot-drink culture indicate that an increased risk of esophageal cancer does indeed exist; the higher temperature does pose a real risk.

But for coffee alone, no clear indication was found of risk associated with coffee drinking -- kind of. "This means simply that the data did not permit a conclusion either that it is safe or that it is dangerous", explained Dr. Loomis. Over one thousand studies in humans and animals were reviewed by the working group. The evidence was found to be "inconclusive" for 20 different cancers.

Studies showed that coffee probably does not increase the risk of breast and prostate cancer and it may on the other hand lower the risk of endometrial and liver cancers significantly. This represents a sea-change from the accepted wisdom in 1991 that coffee was a possible cause of bladder cancer. Coffee now moves from Category 2b ("possibly" carcinogenic to humans) to Group 3 ("not classifiable as to carcinogenicity").

The conclusion is that while "very hot" drinks are likely carcinogenic based on studies from countries where beverages are taken at extremely hot temperatures (around 70C; roughly ten degrees hotter than in North America and Europe), the fear of carcinogenicity in merely drinking coffee itself is groundless. Maybe.

"We say: be prudent, let hot drinks cool down", said Gregory Hartl the WHO's official spokesman in Geneva. The WHO's advice was to "not consume foods or drinks when they are at a very hot - scalding hot - temperature".

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