In the study, published Monday in the Annals of Internal Medicine, drinking "hot" or "burning hot" tea was associated with a two- to fivefold increase in esophageal cancer, but only in people who also smoked or drank alcohol.
Esophageal cancer is the eighth most common cancer in the world and is often fatal, killing approximately 400,000 people every year, according to the International Agency for Research on Cancer. It is usually caused by repeated injury to the esophagus due to smoke, alcohol, acid reflux and -- maybe -- hot liquids.
The study, the largest of its kind, followed close to 500,000 adults in China over an average of 9½ years. Because of the large size, it may set the bar for years to come, according to Neal Freedman, senior investigator at the National Cancer Institute in Bethesda, Maryland, who was not involved in the new research.
Participants who drank tea on a weekly basis were asked to describe its temperature as "warm," "hot" "or "burning hot." Drinking "hot" or "burning hot" tea was not, by itself, a predictor of esophageal cancer, which is good news for tea aficionados.
However, for people who smoked tobacco or drank alcohol -- both of which are known to cause esophageal cancer -- drinking "hot" or "burning hot" tea made their risk of cancer even higher, according to Jun Lv, a professor in the Department of Epidemiology and Biostatistics at Peking University and a lead author on the study.
"Drinking hot tea contributed to cancer only when it clustered with smoking and drinking alcohol excessively," Lv said.
The researchers collected information about tobacco and alcohol consumption at the beginning of the study. "Excessive alcohol consumption" was defined as 15 grams or more of alcohol per day -- slightly more than that found in a 12-ounce glass of beer, a 5-ounce glass of wine or a 1.5-ounce shot of distilled spirits. Tobacco use was defined as one or more cigarettes per day.
Very hot drinks could make the esophagus more vulnerable to known cancer-causing agents such as alcohol and smoke, Freedman said.
"Irritating the lining of the esophagus could lead to increased inflammation and more rapid turnover of the cells," he said. "Alternatively, hot liquids may impair the barrier function of the cells lining the esophagus, leaving the tissue open to greater damage from other carcinogens."
Participants did not objectively measure the temperature of their tea, one of the study's main limitations. However, previous research has suggested that drinking hot beverages at temperatures above 149 degrees Fahrenheit (65 degrees Celsius) could lead to esophageal cancer.
In a 2016 review in The Lancet Oncology, drinking beverages this hot was classified as "probably carcinogenic to humans." The review looked at all types of hot beverages, including coffee and tea. Only some of the studies in the review took alcohol and tobacco use into account.
In the United States and Europe, tea is rarely consumed at temperatures above 149 degrees -- but in places like Russia, Iran, Turkey and South America, it is common to drink tea that hot or even hotter.
"If you go to the Middle East or to Russia, they drink it out of a samovar that's constantly under heat," said Peter Goggi, president of the Tea Association of the USA. "It's very, very hot."
By contrast, "80% of the tea here is iced, so that's a completely different story," he said. "But even in the hot areas, which is in the Northeast and West Coast, most people will be adding something to it, whether it's a little sweetener or lemon," slightly decreasing the liquid's temperature.
Tea also has many health benefits. According to a 2009 study in the journal Nature Reviews Cancer, components of tea leaves have been shown to have antioxidant properties and may protect against other types of cancers, particularly colon and prostate cancer.
"Tea is probably one of the most studied food and beverages in the world today," Goggi said. "Green tea has been shown to be a little more effective in cancer inhibition versus black tea, but black tea has been more effective in cardiovascular health."
So tea drinkers who don't smoke or drink alcohol excessively probably don't need to switch to a different beverage anytime soon, according to Lv.
"Of course, keeping away from both tobacco and excessive alcohol use is the most important means for esophageal cancer prevention," she added.
CNN
