The temperature of our tea or coffee could matter more than we think for our health.
Researchers from the University of Oxford analyzed the habits of 977,282 adults in the United Kingdom. Participants indicated whether they preferred their hot drinks “lukewarm,” “hot,” or “very hot.” Their health was then monitored for an average of more than ten years using medical records.
A cup containing hot coffee.
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The result concerns a specific form of esophageal cancer. Among people who reported drinking their beverages “very hot,” the risk of developing this cancer was about three times higher than among those who preferred them lukewarm. For beverages that were simply “hot,” the risk was about 1.7 times higher.
The esophagus is the tube that carries food and drinks from the mouth to the stomach. The cancer studied develops in the cells lining its wall. It is called esophageal squamous cell carcinoma. The researchers did not find the same association for the other major form of cancer in this organ, adenocarcinoma.
It does not appear to be the tea or coffee itself that is responsible. The association remained linked to heat, regardless of the type of beverage consumed. One possible explanation is that very hot liquids regularly damage the lining of the esophagus. Over time, these repeated injuries could promote the development of cancerous cells.
The amount consumed also seems to matter. After accounting for temperature, drinking at least six hot beverages a day was associated with a 71% increase in the risk of this form of cancer. The study also accounted for known factors such as smoking and alcohol consumption.
However, relative risk must be distinguished from actual risk. This form of cancer remains rare in the United Kingdom, with a lifetime risk close to 1%. A multiplication of the risk therefore does not mean that someone who drinks very hot beverages will inevitably develop the disease. In addition, this study observed an association and does not directly prove that heat causes cancer.
Another important limitation is that the researchers did not measure the temperature of the beverages. Each participant described what they considered lukewarm, hot, or very hot. As a reference point, since 2016 the International Agency for Research on Cancer has classified beverages consumed above 65 °C as probably carcinogenic to humans.
The researchers now want to better determine the temperatures at which the risk actually begins to increase in Western drinking habits. Available studies indicate that tea and coffee are often consumed at around 60 °C in the United Kingdom and the United States, below the 65 °C threshold used in this classification.