Abstract:
A large-scale study by researchers at the University of Oxford in the UK found that drinking hot drinks such as tea and coffee that are too hot may increase the risk of esophageal squamous cell cancer. The study, which tracked nearly 980,000 British adults for up to 14 years, showed that those who said they liked drinking "very hot" drinks were about three times more likely to develop this type of esophageal cancer than those who liked warm drinks.
This study, recently published in the International Journal of Cancer, is one of the largest studies to date on the relationship between the temperature of hot drinks consumed and the risk of esophageal cancer in the UK. Researchers say the study's real focus isn't on the tea or coffee itself, but the temperature at which the beverage is consumed.
The research team used data from the British Biobank and the Million Women Study to conduct long-term follow-up of approximately 980,000 adults. Participants were previously asked at what temperature they usually preferred drinks such as tea and coffee, and researchers then compared this information with long-term health records to see if they were ultimately diagnosed with esophageal cancer.
The results showed that compared with people who said they usually drink "warm" drinks, people who like to drink "hot" drinks have a nearly doubled risk of esophageal squamous cell carcinoma, while people who like to drink "very hot" drinks have an approximately triple risk.
The researchers emphasized that this result does not mean that drinking tea or coffee itself will cause esophageal squamous cell carcinoma. The factor that really correlates with increased risk is the temperature of the drink. In other words, for the same cup of tea or coffee, if you wait for a period of time to cool down, the potential risk may be significantly different from drinking it immediately after boiling.
Esophageal squamous cell carcinoma is one of the main types of esophageal cancer and occurs in the squamous cells that make up the lining of the esophagus. The other major type is esophageal adenocarcinoma, and this study did not find an equally clear link between drinking hot beverages and esophageal adenocarcinoma.
Scientists believe that repeatedly allowing high-temperature liquids to contact the inner wall of the esophagus may cause long-term and repeated thermal damage. During the repeated injury and repair processes of the esophageal mucosa, cells may continue to change, which may increase the probability of cancer after long-term accumulation.
This mechanism may also explain why the relationship between high-temperature beverages and esophageal cancer has also been observed in past studies conducted in other parts of the world. For example, in parts of South America, people have the habit of drinking high-temperature yerba mate, and relevant studies have long found that drinking very high-temperature beverages is associated with the risk of esophageal cancer.
Previous research has also directly measured the temperature of people actually drinking tea. A long-term study of more than 50,000 people in Iran found that people who actually drank at or above 60 degrees Celsius had a higher risk of esophageal squamous cell cancer than those who drank at a temperature below 60 degrees Celsius; if they drank large amounts of high-temperature tea at the same time, the risk would further increase.
The International Agency for Research on Cancer, a subsidiary of the World Health Organization, has previously listed "very hot drinks" with temperatures exceeding 65 degrees Celsius as "possibly carcinogenic to humans". However, 65 degrees Celsius does not mean that a cup of freshly brewed ordinary tea or coffee must reach this temperature, and the drinking habits of different people vary greatly.
This is also one of the important limitations of this British study. Because the study involved nearly a million participants and lasted more than a decade, it was impossible for the researchers to actually measure the temperature of the cup of tea or coffee in the participants' hands at every survey. Therefore, “hot” and “very hot” come primarily from participants’ own subjective descriptions rather than precise temperatures in degrees Celsius.
The researchers were therefore unable to determine a clear "safe temperature line" based on this study. What one person considers a "warm" drink may still be quite hot to another, and there are significant differences in tea and coffee drinking habits in different countries and regions.
The study also suffers from limitations common to observational studies. What the researchers found was a statistical association between drink temperature and cancer risk, not proof that hot drinks directly cause cancer. Therefore, the findings cannot rule out the possibility that other lifestyle factors may have an impact.
However, the findings are generally consistent with a large number of previous studies from other countries and regions, leading the researchers to believe that high temperature itself is likely to be a risk factor for esophageal squamous cell carcinoma.
Notably, the overall absolute risk of esophageal cancer remains relatively low. The lifetime chance of being diagnosed with esophageal squamous cell carcinoma in the UK is around 1%. So even if drinking very hot beverages increases the relative risk several-fold, the absolute increase in risk for someone who is already at very low risk may still not be as large as a "3-fold" number seems.
At the same time, there are some more clear and influential risk factors for esophageal cancer. Smoking and heavy drinking are considered very important risk factors. The importance of quitting smoking and reducing alcohol intake in reducing the risk of esophageal cancer is clearer than simply avoiding a cup of tea that is too hot.
The researchers are therefore not suggesting that people stop drinking tea or coffee entirely, nor are they suggesting that tea and coffee themselves are carcinogenic beverages. On the contrary, tea and coffee themselves contain a variety of bioactive substances, and their health effects have always been an important topic in nutritional research. This study reminds people to focus on "temperature" rather than "beverage type."
For people who like to drink hot tea and coffee, the simplest way is to wait for a while and let the beverage cool naturally to the extent that it will not burn the mouth and esophagus before drinking. This will neither change the drink itself nor significantly increase the cost of daily life, but may reduce the potential risks caused by long-term repeated high temperature irritation to the esophagus.
Scientists are still studying how high temperature causes esophageal cells to become cancerous step by step. An important direction is to observe whether the inner wall of the esophagus will develop persistent inflammation, DNA damage, and abnormal cell repair mechanisms under long-term thermal stimulation. Only by further clarifying these biological mechanisms can we more accurately determine the causal relationship between drinking temperature and cancer risk.
Therefore, the real message of this study is not that "drinking tea and coffee can cause cancer", but rather that "the hotter, the better" should not be regarded as a healthy habit. For those who regularly drink hot beverages, rather than rushing to drink them as soon as they are brewed, it is better to simply wait a few minutes for the temperature to drop to a comfortable level. Existing evidence increasingly supports the view that the real cause for alarm is not tea and coffee, but long-term, repeated exposure to high-temperature beverages that burn the esophagus.
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