The International Agency for Research on Cancer, part of the World Health Organization, revised this week its 1991 determination that classified coffee as possibly carcinogenic. Since then, there have been a lot of studies on the health effects of coffee, so the agency decided to re-evaluate the evidence. On review, the agency determined that coffee drinkers have no reason to worry.
Is this flip-flop a reason to dismiss studies linking cancer to eating bacon, using cell phones or other habits, on grounds that science doesn't prove anything? On the contrary. Scientific understanding of an issue conforms to the best available knowledge, which is constantly progressing. As our knowledge grows and changes, so too might our conclusions.
The 1991 classification was based on a few studies that found associations between drinking coffee and bladder cancer. The World Health Organization noted at the time that the evidence was limited.
Historically, coffee drinkers also tend to be smokers and smoking is a strong risk factor for bladder cancer. Coffee was classified as a possible carcinogen because researchers couldn't confirm whether the association with bladder cancer was an artifact of smoking.
More recent studies have far more robust assessments of smoking as well as more complete evaluations of occupational exposures and other risk factors. When these risk factors are more accurately controlled, a link between coffee and bladder cancer is no longer seen. Taking this new information into account is what caused the agency to revise its previous assessment and conclude coffee drinking is “unclassifiable as to its carcinogenicity"—in other words, there's no evidence it causes cancer.
But the news gets even better for coffee drinkers.
Recent studies have found some evidence that drinking coffee regularly may reduce the risk of liver cancer and endometrial cancer. Other evidence shows coffee may be beneficial in reducing liver disease and type 2 diabetes.
One thing we know for sure: what we eat and drink has a tremendous impact on our health. For more information on healthy eating, visit EWG's Food Scores.
Enjoy your coffee—just go easy on the cream and sugar.
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