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"By denying scientific principles, one may maintain any paradox." – Galileo Galilei

IARC’s Botched Classifications on Coffee

The International Agency for Research on Cancer’s (IARC) Monographs Program has gotten it wrong again – this time on coffee. In 1991, IARC classified coffee as “possibly carcinogenic” to humans based on “a weak positive relationship between coffee consumption and the occurrence of bladder cancer.” Fast forward a quarter of a century later, and IARC (sort of) admitted that its determination was not accurate, and downgraded coffee to “not classifiable as carcinogenic to humans.” In 2016, IARC announced its classification change from “2B” to “3” on its cancer classification scale,
backpedaling its original conclusion:

“The Working Group found that there was inadequate evidence for the carcinogenicity of coffee drinking overall,” its press release reads.

The Many Health Benefits of Coffee

A large body of evidence shows that coffee can be beneficial to your health, casting doubts on IARC’s initial determination. Researchers from the Imperial College London (and, ironically, IARC) recently-published a multinational cohort study, which found an association between consuming coffee and a reduced risk of death from diseases, like circulatory and digestive diseases. IARC scientist and lead author of the study Dr. Marc Gunter even admitted that drinking coffee can be beneficial to your health:

“Our results suggest that moderate coffee drinking – up to around three cups per day – is not detrimental to your health, and that incorporating coffee into your diet could have health benefits.” [emphasis added]

Researchers also found evidence that increased consumption was associated with a reduced risk of death and certain cancers. According to a new study by the University of Southern California (USC), drinking coffee could contribute to a longer life, and may bring additional health benefits. In the July 2017 study, people who drank coffee daily reduced their risk of dying due to heart disease, cancer, stroke, diabetes, and respiratory and kidney disease by 12%. USC’s Dr. Veronica Setiawan even encouraged people to drink coffee:

“If you like to drink coffee, drink up. If you’re not a coffee drinker, then you need to consider if you should start.” Dr. Setiawan continued: “Coffee contains a lot of antioxidants and phenolic compounds that play an important role in cancer prevention.” (emphasis added)

These new studies build upon a vast body of existing research that shows coffee is not a credible cancer risk. Over the past few years, scientists have found that coffee consumption is:

These new findings also complement a wide-body of research that shows how consuming extra coffee helps to curb other ailments and diseases, all-the-while positively impacting brain function:

  • Liver Cirrhosis: A 2016 study, which reviewed data on over 400,000 research participants, found that “two extra cups of coffee a day “was linked to a 44% lower risk of developing liver cirrhosis,” a “potentially fatal” disease. (Those with cirrhosis have an increased risk of liver cancer.)
  • Parkinson’s Disease: Data indicates that “higher coffee and caffeine intake is associated with a significantly lower incidence of PD.”
  • Type 2 Diabetes: According to a study by the American Diabetes Association, there is a “striking (60%) reduction in risk of incident type 2 diabetes in coffee drinkers.”

No wonder an estimated 3.5 billion cups of coffee are consumed worldwide every day.

IARC’s Name Game

Despite the Imperial College London and USC studies, and the numerous other scientific studies that found no link between coffee and cancer, IARC still hasn’t categorized coffee – the second most widely consumed beverage in the world – as Group 4 “probably not carcinogenic to humans,” IARC’s lowest cancer classification. So why is IARC still failing to classify coffee as Category 4: “probably not carcinogenic”? IARC refuses to label coffee — not to mention the hundreds of other substances that it has evaluated with questionable conclusions — as “not carcinogenic” because of its insistence on proving a negative. This was the case with its latest evaluation of coffee, as IARC’s deputy section head Dana Loomis explained:

“We can’t say that it’s completely safe because proving a negative is very difficult, but it has moved down a step in terms of the hierarchy of concern.”

IARC’s insistence not to label substances as “probably not carcinogenic” is because the agency only examines substances that it believes are carcinogenic, based on existing evidence. IARC Director Chris Wilde drives the point home in a letter to NIH director Francis Collins:

“The IARC Monographs only evaluate agents for which there is evidence of human exposure and an existing body of scientific literature indicating a degree of carcinogenic hazard to humans. The non-random selection of agents explains why the evaluations extremely rarely ever find there is ‘evidence suggesting lack of carcinogenicity.’”

So IARC’s puzzling stance on coffee continues: Even though the weight of the evidence does not support that coffee consumption is carcinogenic, IARC has moved coffee down its “hierarchy of concern” rather than removing it completely. Yet, the science supports it should be removed.