Your morning tea or coffee may seem harmless, but drinking it extremely hot could carry an unexpected cancer risk, new research involving nearly 1 million adults suggests

For millions of people, tea or coffee is part of the morning routine. But new research suggests that the temperature at which people drink tea or coffee may be more important to esophageal cancer risk than whether the beverage is tea or coffee.

A large study of nearly one million UK adults has found that people who preferred their hot drinks “very hot” had a substantially higher risk of developing esophageal squamous cell carcinoma (SCC), compared with those who preferred their drinks warm. The findings were published in the International Journal of Cancer by researchers from the University of Oxford’s Nuffield Department of Population Health.

Esophageal squamous cell carcinoma is a type of cancer that begins in the thin, flat cells lining the esophagus, the tube that carries food from your mouth to your stomach.

Nearly 1 million people studied

Researchers Keren Papier, Kezia Gaitskell, Sarah Floud and Gillian Reeves studied the data of 977,282 individuals from the UK Biobank and Million Women Study. Individuals described what they prefer for their hot drinks: "warm", "hot" or "very hot". They also reported daily intake of tea and coffee.

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During the period ranging from 14.2 years in the Million Women Study to 11.1 years in UK Biobank, 2,348 cases of esophageal cancer occurred, including 1,045 cases of squamous cell carcinoma and 1,303 cases of adenocarcinoma.

Subsequently, individuals who prefer hot drinks have 1.7 higher risk of developing esophageal SCC than people who prefer warm drinks, whereas the risk is 3.2 times higher in people preferring very hot drinks.

No similar connection was observed between preference of drink temperature and esophageal adenocarcinoma which is a type of cancer that develops in glandular cells, usually in the lower part of the esophagus near where it joins the stomach.

Temperature, not tea or coffee

The study does not suggest that tea or coffee themselves are responsible for the increased SCC risk. The association remained when researchers considered whether participants primarily consumed tea or coffee, pointing instead toward the temperature of the beverage.

Frequency also appeared to matter. After accounting for drink temperature, people consuming six or more hot drinks a day had a 71% higher risk of SCC than those drinking fewer than six.

However, the researchers did not directly measure the temperature of participants’ drinks. Their categories were based on people's descriptions of how hot they preferred their beverages, meaning the study cannot establish an exact temperature at which the risk begins.

A possible explanation

Scientists believe that frequent exposure to very hot liquids can lead to thermal damage to the lining of the esophagus, which may be part of the mechanism responsible for cancer formation. The scientists from Oxford stated that the temperature association was confined to SCC, which is consistent with a possible thermal-damage mechanism.

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The new results complement previous international studies. The International Agency for Research on Cancer classified consumption of hot beverages at a temperature of more than 65°C as "probably carcinogenic to humans" due to the correlation between the intake of very hot beverages and the development of esophageal cancer.

The risk remains relatively low

Cancer Research UK estimates the lifetime risk of being diagnosed with oesophageal cancer at around 1% for women and 2% for men in the UK. It also stressed that more research is needed because the Oxford study relied on self-creported drink temperature rather than measurements.

Experts speaking to the Science Media Centre similarly said the research demonstrates a robust association but does not by itself prove causation, and warned against interpreting ordinary hot drinks as a major cancer threat. Smoking and alcohol remain much more established risk factors for esophageal cancer.