Why hot drinks could raise your risk of cancer – and how to make sure they’re safe

It can feel like every week, a risk of cancer emerges from an aspect of daily life. The latest threat may come from the ubiquitous experience of drinking a hot cup of tea or coffee. Not all forms of hot drinks, fortunately – only if they are drunk at too high a temperature. A new study suggests that those who drink very hot beverages could triple their risk of getting oesophageal cancer – the tube that connects our throat with our stomach. But how hot is too hot, and how worried should we be? Shorts Why could hot drinks cause oesophageal cancer? The tissues of the mouth and tongue are thicker than the lining of the oesophagus, so a drink temperature that feels tolerable in the mouth could harm the oesophagus. That could lead to inflammation and cells multiplying to repair the damage. The more cells multiply, the greater the chance that some of their DNA randomly develops mutations – the root cause of cancer. “The repair mechanism is constantly replacing dead cells,” said Professor Muy-Teck Teh, an oncologist at Queen Mary University of London, who was not involved with the study. “That predisposes to cancer formation.” How hot is too hot? Concerns first stemmed from higher rates of oesophageal cancer in countries such as Iran, Turkey and South America, where people tend to drink their tea and coffee extremely hot – on average at about 70°C, or sometimes as high as 80°C. That led the World Health Organisation to say drinks over 65°C are “probably carcinogenic”, or cancer-causing, in 2016. But it wasn’t known then that hot beverages could also damage the oesophagus, said Professor Gillian Reeves, a cancer expert at the University of Oxford, who led the study. The average temperature of the hot brews we drink in Britain is about 60°C – although there is great variation. In the new study, published in the peer-reviewed International Journal of Cancer, the subjects didn’t measure the temperature of their drinks – they just reported if they usually had their drinks “very hot”, “hot” or “warm”. Over 14 years, the “very hot” group had three times the rate of a type of oesophageal cancer called squamous cell carcinoma. “It suggests that if we were to reduce the temperature at which those individuals consume tea and coffee, it could lead to a reduction in risk,” said Reeves. Drinking six or more hot beverages a day also increased the risk compared with those who drank fewer, the study found. “More research is now needed to identify the exact drink temperatures linked to this increased risk,” added Dr Keren Papier, senior nutritional epidemiologist at the University of Oxford and lead researcher. What can you do about it? Few people would want to use a thermometer every time they make a brew. But common sense suggests that leaving the drink to cool a little is safer, said Reeves. This is more important with herbal teas, black coffees or other drinks that don’t have added milk, which will bring the temperature down. “Milk is one way of reducing the temperature, but you could also just leave it sit for a few minutes before you start drinking,” said Reeves. How great is this risk? A tripling of the rate of any cancer sounds alarming. But it needs to be set against the relative rarity of this kind of tumour, with about 1 per cent of people ever getting such a diagnosis. An individual’s risk will vary with other factors, such as their genetics and whether they smoke or drink heavily – both of which also cause oesophageal cancer. So, the tripling of risk seen in this study could represent hot drinks raising someone’s lifetime risk from 0.5 to 1.5 per cent, for instance – which still means nearly 99 people out of 100 will not get the cancer. How certain is this cancer link? This kind of study can only show a correlation between drink temperature and cancer, not that one causes the other. Something else could be causing both things; for instance, people with thicker skin lining the throat and oesophagus might tolerate hotter drinks as well as being more naturally predisposed to cancer, said Teh. On the other hand, this kind of correlation-based study is commonly used to identify many other cancer risk factors. And there are several reasons to think this particular one has found a real cause of cancer. One is that there is a plausible mechanism of damage to the oesophagus, supported by animal research. The researchers also found that the “very hot” drink group had the highest cancer rate (three times), the “warm” group had the lowest and the “hot” group were in the middle (1.7 times). This is called a “dose-response relationship” and is seen as further support for the theory being right. Finally, the study showed an increased risk for cancers in the top part of the oesophagus but not for those in the bottom third, which would make sense, as hot drinks would cool by the time they slosh their way down. “It is consistent with the idea that this may well be causal,” said Reeves. “So it adds to the biological plausibility.”