Many people like to start their day with a cup of tea or coffee, but the temperature of your favorite beverage may matter a lot more than you think.
Ten years ago, the International Agency for Research on Cancer (IARC) made headlines by classifying very hot drinks at temperatures above 65°C (149°F) as “probably carcinogenic to humans.”
This 2016 finding followed evidence that mate, a herbal beverage popular in South America and often drunk in very hot temperatures, was associated with an increased risk of esophageal cancer.
Mate is typically consumed at temperatures up to 70°C (158°F), but until now the evidence for consuming hot beverages at cooler temperatures has been inconclusive.
“International research has shown for some time that drinking drinks like mate at very high temperatures, as is the case in South America, is linked to an increased risk of certain oesophageal cancers,” says Keren Papier, a nutritional epidemiologist from the University of Oxford.
“What was less clear was whether this also applied to the temperatures at which hot drinks are typically consumed by Western populations.”
To examine the question, Papier and his fellow researchers analyzed data from two large British cohorts, the Million Women Study and the UK Biobank.
In total, the researchers integrated data from 977,282 participants, in what they claim is the largest study to date examining associations between hot drinks and esophageal cancer.
In both studies, participants were asked similar questions about hot beverage consumption, including how hot they liked their drinks to be (“very hot,” “hot,” “warm,” etc.) and how many cups of tea and coffee they consumed each day.
Researchers found that participants who preferred “piggy hot” drinks had a 3.17 times higher relative risk of developing esophageal squamous cell carcinoma (SCC) during the study period, compared to people who had their drinks “hot,” after accounting for frequency of consumption.
People who reported preferring “hot” drinks had a 69% higher risk of SCC than those who drank “hot” drinks, the researchers found.
Additionally, the data showed that the amount of hot drinks participants consumed was also associated with cancer risk, with those who consumed six or more hot drinks per day experiencing a 71 percent increase in SCC risk compared to people who drank fewer than six hot drinks per day, after accounting for the temperature of the drinks.
The association was similar whether participants primarily drank tea or coffee, and the addition of milk (which was recorded in the Million Women Study) did not appear to significantly change the identified risks associated with temperature.
Although the observational results do not establish that hot drinks cause cancer, the researchers suggest that even a slight reduction in the temperature of hot drinks could potentially prevent a significant number of cases of SCC.
“Assuming a causal association between preferred beverage temperature and esophageal SCC risk, the estimated proportion of esophageal SCC cancers that would be avoided if people consuming beverages at a very hot temperature instead consumed their beverages at a hot temperature is 14 percent,” the study authors write.
“Based on national incidence rates for SCC oesophageal cancers in the UK, these attributable risks translate into an absolute number of cancers that could be prevented each year, which is 440.”
An important limitation of the study, however, is that the researchers did not collect absolute measurements of the temperature of the drinks the participants were drinking – only their self-reported preferences of “very hot”, “hot”, “lukewarm”, etc.
The researchers say future studies could clarify this, but for now they suggest their results could indicate that temperature ranges lower than those cited in the IARC report (above 65°C) may increase cancer risk.
Although their own study did not examine the biological mechanisms involved, the researchers say their results – with similar risks observed with tea and coffee, with or without milk – suggest that the temperature of the drink is the main risk factor, rather than what it contains.
“Animal studies confirm this, showing that very hot water (70°C) promotes precancerous lesions and necrosis of the esophagus, unlike low temperature drinks,” write the researchers.
“The most likely mechanism is thermal injury, which can alter mucosal integrity and promote carcinogenic processes.”
The results are reported in the International Journal of Cancer.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. Although we are proud of our process, we are only human. If you spot an error, please let us know.
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