Does drinking very hot tea cause oesophageal cancer?

Tuesday February 6 2018

"Hot tea linked to deadly cancer in smokers and drinkers," The Daily Telegraph reports.

Researchers found daily tea drinkers in China who also drank 15g of alcohol (almost 2 units) a day and were smokers were more likely to get cancer of the oesophagus (the long tube that carries food from the throat to the stomach) if they drank very hot tea.

People who drank hot tea daily but didn't smoke or drink alcohol every day had no increased risk of oesophageal cancer.

It's unclear whether this study is relevant to people in the UK. The specific type of oesophageal cancer common in China (squamous cell carcinoma) is much less common in the UK, where most cases are adenocarcinoma.

And people in the UK may be less likely to drink scalding-hot tea, especially if they add milk. The practice is reported to be relatively common in China.

The main risk factors for oesophageal cancer are smoking, drinking alcohol, obesity and acid reflux.

People who want to reduce their risk of developing oesophageal cancer would be better advised to tackle these than worry about how much tea they drink.

Of course, it's not a good idea to repeatedly burn your mouth and throat with hot drinks of any sort, so drinking beverages at a sensible temperature is recommended to avoid injury.

Where did the story come from?

The researchers who carried out the study were mostly from China (Peking University, Beijing Institute of Technology, Suzhou Center for Disease Control and Prevention, and the China National Center for Food Safety Risk Assessment) and the University of Oxford in the UK.

The study was funded by grants from the National Natural Science Foundation of China and the National Key Research and Development Program of China.

It was published in the peer-reviewed journal Annals of Internal Medicine.

The Daily Telegraph and The Guardian made it clear in their headlines that the potential risk of drinking hot tea was only relevant to people who smoke and regularly drink alcohol.

This wasn't the case with the Mail Online, running with the headline: "Drinking hot tea increases your risk of oesophageal cancer 5-fold, new study claims".

The story added: "Even those who don't touch alcohol or cigarettes appear to have a higher risk," although the study's results don't bear this out.

The researchers actually stated: "In the absence of both excessive alcohol consumption and smoking, daily tea drinking was not associated with oesophageal cancer risk, regardless of tea temperature."

While the Mail's story goes on to add expert comment stating that people in the UK shouldn't worry, the reporting appears to be designed to alarm readers.

What kind of research was this?

This prospective cohort study is based on a long-running health study of half a million people in China.

Researchers wanted to look at links between hot tea, cigarette smoking and alcohol consumption, as previous studies have shown conflicting results.

Observational studies like this can show links between factors – such as tea drinking and cancer – but can't prove that one causes another, as it's not possible to account for all the potential alternative explanations for the link.

What did the research involve?

Researchers used data from the China Kadoorie Biobank project, which measures health data in half a million participants across China.

They selected 456,155 people aged 30 to 79 who didn't have cancer at the start of the study.

They were asked about their lifestyle – including tea consumption habits – and followed for an average of 9.2 years.

Researchers looked at how many people got oesophageal cancer and whether they were more likely to drink hot tea, drink alcohol regularly, or smoke cigarettes.

"Heavy" alcohol consumption was classified as 15g of alcohol a day – almost 2 units (1 unit is 8g). The recommended limit for men and women in the UK is 14 units a week, or 2 a day.

People were asked how often they drank tea, how strong they made it (in grams of tea leaves), the type of tea (for example, black or green tea), and whether they drank it at "room temperature, warm, hot or burning hot".

Researchers excluded people who'd reduced their tea or alcohol consumption or stopped smoking in the 6 months before the study started.

The researchers adjusted their figures to take account of the following potential confounding factors:

  • age and sex
  • education, marital status and household income
  • tobacco smoking and alcohol consumption
  • physical activity
  • dietary intake of red meat, fruit and vegetables
  • body mass index
  • family history of cancer
  • menopausal status

What were the basic results?

Of the 456,155 people in the study, 42% of the men and 16% of the women drank tea daily.

There were 1,731 cases of oesophageal cancer over 9.2 years, nearly two-thirds of which were in men.

Cases were identified from cancer and death registries and self-report during follow-up.

Researchers were only able to confirm oesophageal cancer from laboratory records for 569 people, and most of these were squamous cell cancer cases.

For those who drank more than 15g of alcohol a week, drinking burning hot tea daily doubled the risk of oesophageal cancer, compared with alcohol drinkers who drank tea less than once a week (hazard ratio (HR) 2.16, 95% confidence interval (CI) 1.49 to 3.14).

For people who drank less than 15g of alcohol a week, the additional risk of cancer from hot tea consumption (compared with tea less than weekly) was only on the borderline of statistical significance (HR 1.26, 95% CI 1.00 to 1.86). This shows a lot of uncertainty about this result.

For smokers, drinking burning hot tea increased the risk of cancer by 53%, compared with smokers who drank tea less than once a week (HR 1.53, 95% CI 1.15 to 2.03).

Drinking burning hot tea wasn't linked with risk of oesophageal cancer in non-smokers.

Compared with people who didn't drink alcohol daily, smoke or drink hot tea, people who did all of these had a 5-fold increased risk of oesophageal cancer (HR 5.01, 95% CI 4 to 6.28).

The researchers also found that people who reported taking their tea burning hot were also more likely to smoke, drink alcohol daily, drink more cups of tea a day, and take stronger tea.

How did the researchers interpret the results?

The researchers said that people who "drank high-temperature tea, consumed alcohol excessively, and smoked had an oesophageal cancer risk more than 5 times greater than those who had none of these 3 habits.

"However, in the absence of both excessive alcohol consumption and smoking, daily tea drinking was not associated with oesophageal cancer risk, regardless of tea temperature."

They said: "Abstaining from hot tea might be beneficial for preventing oesophageal cancer in persons who drink alcohol excessively or smoke."

Conclusion

In comparison with the harms of drinking excessive alcohol or smoking tobacco, drinking tea is an innocuous pastime.

This study shows that drinking very hot tea every day might exacerbate the risks posed by alcohol and tobacco, perhaps by damaging the skin cells so the throat has less protection against the harms they cause.

But drinking tea isn't linked to higher cancer risk on its own.

This study has some limitations. As an observational study, it can't prove whether one factor causes another.

People were only asked about tea, alcohol and tobacco consumption at the start of the study. We don't know if they changed their habits over the course of 9 years of follow-up.

The reports about alcohol, tobacco and tea consumption weren't independently verified.

Similarly, the temperature of the tea wasn't checked – researchers relied on people saying whether they usually drank tea warm, hot or burning hot.

Even in this sample, oesophageal cancer was relatively rare – and the absolute increase in risk from hot tea was quite small.

For example, for those who drank more than 15g of alcohol a week, there were around 1.2 cancers per 1,000 people per year, rising to 1.7 per 1,000 for those who drank burning hot tea.

For non-drinkers and non-smokers, the risk was less than 0.5 per 1,000 per year, regardless of how much tea they drank or how hot they drank it.

It's not clear whether these results apply to the UK. Our tea drinking habits (where the majority of people drink black tea with milk) and other lifestyle risk factors for oesophageal cancer may differ from China.

As several experts have commented, most oesophageal cancers in the UK are adenocarcinoma rather than squamous cell. The different disease development may be the result of different exposures and risk factors.

The researchers' conclusion that people who smoke and drink excessively might want to cut out hot tea seems odd.

People would be far better advised to stop smoking and drink less alcohol to avoid the many risks that these habits carry. Drinking tea is unlikely to be the biggest of their health problems.

Analysis by Bazian
Edited by NHS Website