Piping hot beverages have been linked to cancer of the esophagus.

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Twenty-five years ago, the World Health Organization rated coffee as "possibly carcinogenic." Now the agency is reversing its longstanding warning, declaring that evidence is lacking. (Whew!) But the WHO is also saying that hot drinks, of any kind, may cause esophageal cancer.

In a report published today in The Lancet Oncology, the WHO's International Agency for Research on Cancer said a working group of 23 scientists had classified drinking very hot beverages at or above 65 degrees C (149 degrees F) as "probably carcinogenic to humans." (A cup of coffee or tea is typically served between 160 and 185 degrees F.)

The IARC’s job is to classify foods, chemicals, and other items into one of five categories: carcinogenic to humans, probably carcinogenic to humans, possibly carcinogenic to humans, not classifiable, and probably not carcinogenic. Things like tanning beds and smoking are in the first category because evidence indicates they definitely cause cancer. Hot beverages are now in the second category because the research linking them to cancer isn't as strong.

The working group's conclusion was based in part on studies done in countries (including China, Turkey, and South America) where tea or mate is traditionally drunk piping hot. The research showed that the risk of esophageal cancer "increased with the temperature at which the beverage was drunk," according to a statement from the WHO.

The IARC also cited studies done on animals that suggested water hotter than 65 degrees C can promote the growth of tumors.

Esophageal cancer is the eighth most common cancer worldwide, causing 5% of all cancer deaths. About 15,000 Americans are diagnosed with the disease each year.

"Smoking and alcohol drinking are major causes of esophageal cancer, particularly in many high-income countries," Christopher Wild, Director of the IARC, said in the statement. "However, the majority of cases occur in parts of Asia, South America, and East Africa, where regularly drinking very hot beverages is common and where the reasons for the high incidence of this cancer are not as well understood."

The WHO's spokesman in Geneva, Gergory Hartl, told Reuters that the new classification was based on limited evidence, and that more research is needed. But in the meantime, the agency is suggesting people avoid sipping anything scalding hot: "We say: be prudent, let hot drinks cool down."