A Study Showing The Dangers Of Hot Tea Reveals How Complex Cancer Risks Can Be

There are few better things to help soothe a stressful day than a spot of hot tea. But a new study published yesterday 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 oesophageal cancer. The findings also highlight how complicated it can be to figure out what exactly causes cancer.

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

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 1731 people who were diagnosed with oesophageal cancer.

They found that people who said they drank hot or burning hot tea were more likely to get oesophageal 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 15g of alcohol (about a standard serving) daily were five times as likely to develop oesophageal 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."

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 oesophageal 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."

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 oesophageal 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 Organisation's International Agency for Research on Cancer classified hot beverages as a Class 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 control for other risk factors such as 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 oesophageal cancer. But because much fewer women drank tea, had oesophageal 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 per cent of men were regular tea drinkers, for instance, only around 16 per cent of women were.

It's also worth remembering that while oesophageal cancer is a very serious and often fatal disease that killed 1329 people in Australia in 2015, it's relatively rare. According to the US National Cancer Institute, an estimated 0.5 per cent of men and women are expected to be diagnosed with oesophageal cancer during their lifetime. Breast cancer for comparison - the risk of which is also raised by drinking and smoking - will affect around 12 per cent 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 18C - 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 favour, but the rest of your body will appreciate it, too.

[Annals of Internal Medicine]

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