Relax, your cup of tea isn’t trying to kill you. Probably. Photo: Getty

There are few better things on a blustery cold day than a spot of hot tea. But a new study published Monday in the Annals of Internal Medicine suggests that some people’s tea habits—in particular, those who drink and smoke regularly—might be raising their chances of developing esophageal cancer. The findings also highlight how complicated it can be to figure out what exactly causes cancer.

Researchers examined data from an ongoing population study known as the China Kadoorie Biobank study. The study collected physical measurements and health-related questionnaires from more than half a million adults living throughout the country from 2004 to 2008. Ever since then, it’s kept track of their health outcomes. The researchers focused on some 400,000 people free of cancer at the start of the study. By 2015, there were 1,731 people who were diagnosed with esophageal cancer.

They found that people who said they drank hot or burning hot tea were more likely to get esophageal cancer, but only if they also drank alcohol or smoked often. Both drinking and smoking are already known risk factors for that type of cancer.

People who drank both burning hot tea and more than 15 g of alcohol (about a standard serving) daily were five times as likely to develop esophageal cancer than those who drank tea and alcohol less than once a week. Similarly, current smokers who drank burning hot tea daily were twice as likely to develop cancer. And the risk was higher still for people who engaged in all three habits.

“I think the results are really important,” Catherine Carpenter, an associate professor of clinical nutrition at UCLA, told me. “[But] there isn’t any question about whether tea in of itself is carcinogenic. It’s not about that, it’s about having a lifetime history of drinking very hot beverages.”

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Regular tea consumption is even linked to a lower risk of some cancers, she added.

China has long been known to have relatively high rates of esophageal cancer, which has led to speculation that the country’s love of hot tea might play a part. But the findings also illustrate how complex cancer can be.

“Probably all cancers have more than one cause, and what makes it so challenging that some people can develop the same cancer, but for different reasons,” Carpenter said. “That’s what makes the study of cancer so hard.”

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The study suggests that smoking, drinking, and the scalding damage caused by hot temperatures seem to build on top of one another to substantially increase our chances of esophageal cancer, creating a “lethal cocktail,” Carpenter said. But studies conducted elsewhere have also found an increased cancer risk from hot drinks alone. Based on that evidence, the World Health Organization’s International Agency for Research on Cancer classified hot beverages as a Group 2A agent in 2016, deeming it was “probably carcinogenic” to people. (At the same time, it also absolved just plain old coffee as being specifically problematic.)

So it might be the case there’s still a small risk from constantly drinking hot things, or that previous research was somehow flawed and didn’t adequately control for other risk factors like drinking and smoking.

The connection between hot tea and cancer was also much shakier for women, even when smoking and drinking was taken into account. That could mean that gender plays an inherent role in causing esophageal cancer. But because much fewer women drank tea, had esophageal cancer, and smoked and drank regularly, it might just mean there wasn’t a large enough sample size from which to draw any solid conclusions. While 40 percent of men were regular tea drinkers, for instance, only around 16 percent of women were.

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It’s also worth remembering that although esophageal cancer is a very serious and often fatal disease that is estimated to kill around 400,000 people annually, it’s relatively rare. According to the National Cancer Institute, an estimated 0.5 percent of men and women are expected to be diagnosed with esophageal cancer during their lifetime. Breast cancer for comparison—the risk of which is also raised by drinking and smoking—will affect around 12 percent of women.

The researchers, based on their results, advocate that alcohol drinkers and smokers think about cooling down their tea. The study didn’t ask about the specific temperature of tea that drinkers regularly had, but research elsewhere has found that the cancer risk drops off completely for beverages under 65 degrees Celsius*—a level most people already drink tea and coffee at.

And while that’s sound enough advice, it’s also true that at the end of the day, you’d get more bang for your buck by cutting down on the other two things. Not only would you be doing your throat a favor, but the rest of your body will appreciate it, too.

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[Annals of Internal Medicine]

*This article originally cited 65 degrees Fahrenheit as the upper limit for people to safely drink their hot beverages at. The actual limit referenced by the linked research is 65 degree Celsius, which equates to 149 degrees Fahrenheit. We regret the error.