Hot coffee could cause oesophageal cancer

The cooler it is, the safer

A steaming hot drink may feel invigorating or comforting. But research suggests that it is best to let it cool off before you take a sip. A study published on September 8th in the International Journal of Cancer adds to a growing body of evidence that drinking very hot beverages of any kind increases the risk of cancer of the oesophagus (the part of the alimentary canal connecting throat to stomach).

The cooler it is, the safer (unsplash)

This new investigation is an analysis of data on the tea- and coffee-drinking habits of nearly 1m adults in Britain. Those who said they preferred their beverages “hot” or “very hot” rather than “warm”, it found, had an increased risk of subsequently developing a type of oesophageal cancer that is called squamous-cell carcinoma.

The risk was three-fold higher for those drinking “very hot” tea or coffee. For those drinking them “hot” it was elevated to a lesser degree. If all those who drink their beverages very hot cooled them to hot, that might prevent 440 of the 3,200 British cases a year.

The results held regardless of whether people’s usual drink was tea or coffee, or whether they added milk—evidence that it was the temperature of the drink that mattered, rather than what was in it. And studies from other parts of the world have linked other hot drinks, including green tea and mate (a herbal infusion popular in South America), to oesophageal cancer. In 2016 the International Agency for Research on Cancer, or IARC (part of the World Health Organisation), classified the drinking of very hot beverages as “probably carcinogenic”, meaning that the evidence for a causal effect was substantial, even though not fully definitive. The evidence from human studies is based on observational data (which cannot prove that the link with cancer is causal). But experimental studies in animals point in the same direction.

How hot is too hot? At the time IARC reviewed the scientific evidence, the available data suggested that the cancer risk goes up at drinks temperatures above 65°C. The new British study did not record drinks’ temperatures. Rather, it was up to participants to judge what drink temperature was warm, hot or very hot. Other investigations have found that the typical temperature of hot drinks in Britain and America is around 60°C. The study participants who said they drank their brew “warm” were, therefore, probably sipping it cooler than that. The takeaway message is, though, that the less hot your drink is, the better, says Gill Reeves from Oxford University, one of the study’s authors.

Carrying a thermometer around to dip in your take-away cappuccino is not particularly practical and may earn you odd looks. What you can do, instead, is simply wait for your drink to cool down.

For useful guidance on how long to wait, consider the “cupping protocol” for professional coffee tasters published by the Specialty Coffee Association, a trade group. After brewing the grinds for four minutes, the pros wait and sniff for eight to ten minutes, which they reckon is enough time for the coffee to cool down to about 70°C. That is the temperature prescribed for doing the first slurp, from a spoon (known as the “is this acceptable” pass). They then wait five to eight more minutes, which usually brings the coffee to about 55°C. That, according to boffins, is the best temperature for rating the flavour and taste. If you are in a hurry, though, and simply looking for a caffeine boost, adding some cold water or milk from the fridge would do.