LONDON, UK — Regularly drinking tea, coffee and other beverages at very high temperatures may increase the risk of oesophageal cancer, a major UK study suggests, with researchers warning that scalding liquids can damage the lining of the food pipe.
The study by researchers at the University of Oxford involved nearly one million middle-aged men and women and is described as the largest study to date examining the relationship between hot drink consumption and oesophageal cancer.
People who reported drinking beverages that were “very hot” had about three times the risk of developing the cancer compared with those who drank their beverages at warmer temperatures.
Researchers, however, stressed that the overall risk of developing oesophageal cancer remains relatively low.
The findings were published in the International Journal of Cancer.
Drinks above 65°C classified as very hot
The study defined beverages served at 65°C or above as “very hot”.
Researchers said repeated exposure to steaming-hot liquids may damage the cells lining the oesophagus as the drink travels from the mouth to the stomach.
The findings were based on data from 977,282 participants, making the research one of the largest investigations into the possible association between beverage temperature and oesophageal cancer.
The researchers also found that consuming six or more hot drinks a day was associated with a higher risk.
Adding milk may reduce the temperature of tea or coffee slightly, but researchers cautioned that a drink can remain dangerously hot even after milk has been added.
Boiling tea can be much hotter than 65°C
A freshly brewed drink can reach temperatures considerably higher than the level identified in the study.
Water reaches about 100°C when it boils. Tea or coffee prepared immediately after a kettle has boiled may initially be around 90°C to 95°C, depending on how it is prepared and the container used.
That means a drink that feels comfortably warm after several minutes may be significantly cooler than one consumed immediately after preparation.
Health experts therefore advise people to allow very hot beverages to cool before drinking them.
Cancer Research UK says there is no single exact waiting time that applies to every drink because cooling depends on factors such as the volume of liquid and the type of cup.
Its advice is simply to wait until the drink is comfortable to consume rather than drinking it while it is still extremely hot.
How hot is too hot?
The Oxford study’s 65°C threshold provides a useful research benchmark, but the researchers said more work is needed to establish precisely which temperatures are associated with increased cancer risk.
Lead researcher Dr Keren Papier said previous research in South America had also identified a possible relationship between consuming extremely hot drinks and oesophageal cancer.
The region has long had a tradition of drinking mate, a herbal beverage that is sometimes consumed at very high temperatures.
Papier said further research was needed to determine the exact beverage temperatures that may be linked to the increased risk.
The issue is particularly relevant because people’s perception of whether a drink is too hot can vary considerably.
A separate study involving 118 young adults found that participants generally considered black coffee too hot at temperatures of about 70°C or higher after tasting beverages at different temperatures.
Commercial coffee temperatures can also vary widely.
One takeaway coffee cup manufacturer cited an ideal serving range of approximately 49°C to 60°C, while coffee requested as “extra hot” may be served at temperatures exceeding 82°C.
Overall cancer risk remains low
Despite the apparent association, researchers stressed that the absolute risk of developing oesophageal cancer remains relatively small.
The study suggests that approximately one or two out of every 10 oesophageal cancer cases could potentially be avoided if people stopped consuming beverages at very high temperatures.
Squamous cell oesophageal cancer is relatively uncommon, affecting a few thousand people each year in the UK.
The lifetime risk of developing this type of cancer is estimated at around 1pc of the population, meaning that even a substantial increase in relative risk does not mean that most people who drink hot tea or coffee will develop the disease.
The distinction between relative risk and absolute risk is important.
A threefold increase in risk can sound alarming, but when the underlying probability of a disease is low, the resulting individual risk may still remain comparatively small.
Smoking and alcohol remain major risk factors
Very hot beverages are only one of several factors that may influence the risk of oesophageal cancer.
Smoking and alcohol consumption are established risk factors and can have a greater impact on an individual’s likelihood of developing the disease.
Cancer Research UK researcher Fiona Osgun said the most important steps people can take to reduce their risk include avoiding smoking and reducing alcohol consumption.
The advice means people should not interpret the new findings as suggesting that beverage temperature is the primary cause of oesophageal cancer.
Instead, the research adds to evidence that repeated exposure to extremely hot liquids may be one factor contributing to the development of the disease.
Symptoms to watch for
Oesophageal cancer develops in the food pipe, the tube connecting the throat to the stomach.
Possible symptoms include:
- Persistent heartburn or indigestion
- Pain or discomfort in the throat or chest
- Difficulty swallowing
- Unexplained weight loss
These symptoms can have many causes and do not necessarily indicate cancer.
However, people experiencing persistent or unusual symptoms should seek medical advice rather than attempting to diagnose themselves.
Simple step can reduce exposure
For tea, coffee and other hot beverages, allowing the drink to cool before consuming it is a simple way to reduce exposure to extremely high temperatures.
The researchers do not suggest that people need to stop drinking tea or coffee altogether.
Instead, the evidence points towards avoiding beverages that are hot enough to cause discomfort or scalding.
The findings also highlight the importance of considering how hot a drink is, rather than focusing only on the type or quantity consumed.
For most people, waiting a few minutes before drinking a freshly prepared beverage may substantially reduce its temperature.
The Oxford study provides further evidence of a possible link between very hot beverages and oesophageal cancer, but researchers say more work is needed to establish the precise temperatures and mechanisms involved.
For now, experts say the practical message is straightforward: if a drink is too hot to comfortably sip, allow it to cool first.
