The list of cancer-causing agents is long—and getting longer. Experts already tell us to avoid smoking, exposure to UV radiation from the sun and even air pollution because these can increase the risk of cancer. Now the World Health Organization says that hot drinks like coffee, tea and maté belong on that list too. The group’s International Agency for Research on Cancer (IARC), made up of 23 scientists from 10 countries, reviewed around 1,000 studies that investigated a connection between high-temperature beverages and their potential link to cancer. Based on the available evidence, they conclude that drinking very hot beverages, which they defined as anything above 149F (65C)—cooler than a cup of coffee from most take-out spots—is linked to higher risk of cancer of the esophagus.
They based their conclusion, which is published in Lancet Oncology, on studies that found higher rates of esophageal cancer among people who drank extremely hot tea or coffee compared to those who consumed their drinks at lower temperatures. The link to cancer remained strong even after they adjusted for things like smoking and other possible cancer risk factors. Animal studies also seem to hint that even very hot water can increase the risk of this type of cancer, presumably because the temperature scalds delicate tissues in the esophagus; that damage may then trigger more rapid turnover of the cells, which can in some cases lead to out-of-control malignant growth.
The report also concludes, however, that there isn’t adequate evidence to classify coffee itself as a carcinogen. That’s a downgrading of the risk for coffee from its previous analysis, done in 1991, when studies linking coffee consumption to a higher risk of bladder cancer led the IARC to deem coffee as "possibly" carcinogenic to people. Now, says Dana Loomis, deputy head of the IARC, “the available scientific evidence base is much larger and stronger. There are quality studies available today that are significantly better than those in 1991.” Recently, more studies that control for such factors support the benefits of coffee in lowering risk of cancer in certain parts of the body. But for 20 other types of cancer, the evidence isn’t strong enough to suggest either a benefit or risk, so the IARC is changing the designation to “inadequate evidence for carcinogenicity of coffee drinking overall.”
That seems to contradict the finding about hot beverages, since most people drink their coffee hot. But the classifications aren’t necessarily mutually exclusive. People who drink more coffee seem to have lower rates of certain cancers, including liver and endometrial cancers. But, says Dr. Otis Brawley, chief medical and scientific officer at the American Cancer Society, “that’s not where hot beverages hit. Hot beverages hit the mouth, throat, esophagus and stomach.” So that means that even though coffee may be hot, as long as it’s not too hot, there doesn’t seem to be evidence linking coffee to higher risks of cancer other than esophageal cancer.
In the studies the group reviewed, there seemed to be an increased risk of esophageal cancer only when people drank very hot beverages, usually above 149F. The National Coffee Association USA recommends holding coffee at 180 to 185F; most coffee sellers serve their drinks at about 10 degrees below that after a lawsuit by a customer who was scalded by cup at the holding temperature at McDonald’s—but that's still higher than experts now recommend to avoid cancer risk.
The people who might want to discuss the latest classification change with their doctors are people with Barrett’s esophagus, a condition that often precedes esophageal cancer. For almost every else, says Brawley, the risk from the higher temperature drinks is much smaller than the risk from other, more common risk behaviors. “I would say anybody who drinks alcohol shouldn’t even worry about this because alcohol is far more of a cancer-causer than coffee or hot drinks. Anybody who smokes cigarettes also shouldn’t worry about this because cigarettes are a far greater cause of cancer than alcohol.”
“Basically this is a reassuring message for coffee drinkers,” says Dr. Alberto Ascherio, professor of nutrition and epidemiology at Harvard T. H. Chan School of Public Health. Just don’t drink it too hot.