Coffee isn’t likely to give you cancer after all, the World Health Organization’s cancer agency announced on Wednesday, and might reduce the risk of some cancers.
Unless it’s really, really hot — like 150 degrees Fahrenheit or higher, or almost too hot to drink — in which case it might indeed promote cancer.
That somewhat confusing message emerged from the latest assessment of coffee and other hot drinks by the International Agency for Research on Cancer, which periodically assesses the carcinogenicity of substances from red meat (“probably carcinogenic to humans”) to the radiation from cell phones (“possibly” so).
Back in 1991, IARC classified coffee as “possibly carcinogenic” to people. That determination was based on studies finding “limited evidence” that coffee drinkers had a higher incidence of bladder cancer than people who did not. The qualifier “possibly” reflected countervailing studies finding that coffee drinkers had lower rates of breast and colorectal cancer, as well as little evidence of carcinogenicity when lab animals were given coffee.
Looking to update that assessment, IARC last month convened 23 scientists from 10 countries to reevaluate the carcinogenicity of coffee, as well as mate (a tea-like, high-caffeine drink popular in South America), and “very hot beverages.”
This time, the body of evidence — which has “become much larger and much stronger” since 1991, IARC’s Dr. Dale Loomis told reporters — exonerated coffee.
More than 1,000 observational studies have compared coffee drinkers to abstainers. The 23 scientists advising IARC gave the greatest weight to research that followed coffee drinkers and coffee abstainers over many years. They also looked closely at studies that compared drinkers and abstainers at a single point in time but did a good job of separating out other factors that might account for any differences in cancer incidence. Perhaps coffee drinkers also smoke more, for instance.
The totality of such evidence produced “no consistent evidence” linking coffee to bladder cancer, which had been the chief concern back in 1991, IARC said in a statement issued on Wednesday. Nor was there evidence that drinking more coffee raised the risk of cancer more than drinking a little.
What’s more, a 2012 analysis of 16 individual studies found that coffee drinking was associated with a lower risk of endometrial cancer. A 2016 analysis of 12 earlier studies found that the risk of liver cancer falls about 15 percent for each cup of coffee drunk per day. And some 40 studies found either no connection between coffee and breast cancer or a slightly protective effect.
And so it went for some two dozen other cancers from lung and colorectal to ovarian and pancreatic.
A handful of studies did find a higher rate of cancer in coffee drinkers, but only in men, which could be explained by the fact that coffee-drinking men were more likely to be smokers or to be exposed to chemical carcinogens at work than peers who didn’t drink coffee.
All that led IARC to conclude “that there is inadequate evidence in humans for the carcinogenicity of coffee drinking.” But the agency did not go so far as to give coffee its “probably not carcinogenic” label. In nearly 1,000 carcinogenicity assessments, IARC has exonerated only a single substance — caprolactam, a compound used to make nylon — which has made it the target of vehement criticism.
Mate, the South American drink, was, like coffee, classified in 1991 as “probably carcinogenic to humans.” That was largely based on single-point-in-time studies finding that South Americans hospitalized for cancer of the esophagus were more likely to be mate drinkers.
But further analysis showed that the mate-cancer link held only for mate that was drunk “hot” or “very hot,” IARC said.
That got IARC looking at scalding-hot drinks in general, partly because a link to cancer wasn’t completely crazy, biologically: very hot drinks can damage the cells of the throat and digestive tract, possibly in ways that could trigger cancer. The experts indeed found a 2000 analysis of case-control studies — the weakest kind — finding a “significantly increased” risk of esophageal cancer from very hot tea and other drinks.
“There is limited evidence in humans for the carcinogenicity of drinking very hot beverages,” the IARC experts concluded. That includes (based on experiments in lab animals) water hotter than about 150 degrees Fahrenheit, making very hot water also “probably carcinogenic to humans.”
Although coffee masters recommend a water temperature of 195 to 205 degrees Fahrenheit for brewing, and it is often served nearly that hot, for most people a drinkable temperature is about 136 degrees. “Surveys show that people in Europe and North America prefer a temperature for their coffee or tea of less than 60 degrees Celsius,” or 140 degrees Fahrenheit, Loomis said. If java addicts wanted to reduce their risk of developing esophageal cancer from scalding liquids scouring their tissue, he added, “they could wait a few minutes” and let their brew cool off a little.