Drinking very hot tea and coffee triples the risk of developing cancer of the gullet, the world’s largest study of the link between them has found.
The findings show that people should let very hot cups of tea and coffee cool down until they are comfortable to drink, in order to reduce their risk of the disease, cancer experts said.
The temperature of the drink and the number of very hot drinks someone consumes increase the chances of getting oesophageal squamous cell carcinoma (SCC), the research found. However, hot drinks do not heighten the risk of getting adenocarcinoma (AC), the other form of oesophageal cancer.
“Consumption of drinks at a ‘very hot’ versus ‘warm’ temperature was associated with a threefold greater SCC risk but not with AC risk, after adjustment for consumption frequency”, according to the study, which was published on Wednesday in the International Journal of Cancer.
“After controlling for drink temperature, daily consumption of six or more versus fewer than six hot drinks was associated with a 71% increase in SCC risk, with little association with AC risk”, said researchers. The study was led by Dr Keren Papier, a senior nutritional epidemiologist at the University of Oxford’s population health department.
The findings are based on analysis of the consumption of hot drinks by almost 980,000 people in the UK – the largest number of people globally in any related studies to date. It followed participants over 14 years to give a long-term picture of their habits and health.
They were asked how they preferred to consume hot drinks. Available answers included “very hot”, “hot”, “warm” and “do not drink hot drinks”. The conclusions were based on people’s estimation of how hot the drinks were that they had consumed rather than their exact temperatures.
The study produced conclusions for a western European population that mirrored similar findings already seen in studies conducted in Asia, Africa, South America and the Middle East, which found that drinking tea or mate – a caffeinated herbal drink popular in South America – at or above 70C increased the risk of oesophageal cancer.
The International Agency for Research on Cancer, part of the World Health Organization, said in 2016 that hot drinks were “probably carcinogenic to humans” and “one probable cause of oesophageal cancer”. They are thought to heighten the risk of the disease by causing heat damage to the cells which line the oesophagus, which is also known as the body’s foodpipe. Alcohol and smoking are other major risk factors for that type of cancer.
Health authorities could use these latest findings to encourage the public to consume cooler drinks and fewer very hot drinks to help ensure that fewer people are diagnosed with that form of oesophageal cancer, the study team said.
For example, one in seven cases of SCC in the UK “could be avoided if individuals who reported consuming their drinks at a ‘very hot’ temperature instead consumed them at a temperature more representative of the temperature range described as ‘hot’.
The researchers said: “The fact that we observed a clear trend in risk across self-reported temperature categories suggests that further limiting the temperature at which individuals consume their drinks to something well below average for this population may well avoid an even greater proportion of SCC cases.
“This large UK study of middle-aged adults, amongst whom hot drinks are widely consumed, provides clear evidence that temperature and frequency of hot drink consumption represent useful targets for SCC prevention.”
Fiona Osgun, the head of health information at Cancer Research UK, which funded the study, said: “It’s difficult to put an exact time on how long a hot drink should be left to cool. But if you’re worried, we’d suggest just waiting until it’s comfortable to drink rather than drinking it while it’s still very hot.”
However, the charity does not believe that cafes, coffee shops and restaurants should start serving tea and coffee at a lower temperature in order to reduce the risk of SCC.
Muy-Teck Teh, a professor of molecular oral oncology at Queen Mary University of London, said the research’s reliance on self-reported temperatures may have affected the findings.
“A key limitation, however, is that perceived drink temperature is inherently subjective, and it remains unclear whether individuals who tolerate or prefer very hot drinks have altered thermosensation or mucosal sensitivity that might itself reflect underlying biological predisposition to squamous cell carcinoma and lead them to prefer hotter drinks.
“This possibility cannot be excluded and complicates interpretation of causality”, he added.
