How hot is too hot? Oxford study flags cancer risk from very hot drinks

Coffee and tea are a daily ritual for several people, and they are very particular about the choice of milk and sweetener added to their beverages, but according to scientists, there's another factor worth considering. Are you drinking your beverage too hot?

Research on hot beverages

As per a research led by scientists at the University of Oxford, people who regularly consume beverages at very high temperatures may have a greater risk of developing oesophageal squamous cell carcinoma (SCC), a form of cancer affecting the food pipe.

The findings came from a study involving nearly one million adults in the UK. Participants who described their drinks as “very hot” were found to have roughly three times the risk of developing oesophageal SCC compared with those who generally consumed their beverages warm.

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However, the study does not mean tea or coffee itself causes cancer.

What did the study find?

Researchers from Oxford Population Health analysed information from approximately 980,000 adults participating in the UK Biobank and Million Women Study.

Participants who consumed hot drinks were asked to describe their usual drinking temperature as “warm”, “hot” or “very hot”. Their health records were then followed for more than a decade to identify cases of oesophageal SCC.

The analysis showed a clear difference between the groups. Compared with people who preferred warm drinks, those who reported drinking hot beverages had an approximately 1.7-fold greater risk of oesophageal SCC. For those who preferred their drinks very hot, the risk was about three times higher.

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Dr Keren Papier, lead researcher and senior nutritional epidemiologist at Oxford Population Health, said "International research has shown for some time that drinking beverages like maté [a drink popular in South America] at very high temperatures … is linked to increased risk of certain oesophageal cancers," as quoted by Cancer Research UK. "What was less clear was whether this also applied to the temperatures at which hot drinks are usually consumed in western populations. This is now the largest study to look at that question in a UK population, where many people drink tea and coffee daily. It adds to existing evidence that drinking very hot drinks could increase the risk of oesophageal squamous cell carcinoma."

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How can hot drinks affect oesophagus?

The researchers classified a beverage at 65 degrees Celsius or above as “very hot”. That is considerably cooler than freshly boiled water. Water coming directly from a kettle can reach approximately 100 degrees Celsius, while tea or coffee immediately after preparation can still be around 90-95 degrees Celsius after being poured into a cup.

The oesophagus is the muscular tube that transports food and liquid from the mouth to the stomach. Extremely hot liquids can expose its lining to thermal injury, and as per scientists, repeatedly exposing the tissue to very high temperatures could cause irritation and damage. Continued injury and repair may, over time, contribute to cellular changes associated with cancer development.

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"More research is now needed to identify the exact drink temperatures linked to this increased risk," Papier said.

The researchers also observed a link between consuming larger quantities of hot beverages and oesophageal SCC. People who reported drinking six or more hot beverages a day had a higher risk than those consuming fewer.

However, that finding should not be interpreted as meaning that drinking several cups of tea or coffee will inevitably result in cancer.