Very hot drinks triple the risk of food-pipe cancer - critical summary review

The esophagus, also called the food pipe, is the muscular tube that carries everything you swallow from your mouth to your stomach. Two very different cancers can develop in it. One, adenocarcinoma, starts in the glands of the organ and is associated with reflux disease and Barrett's esophagus. The other, squamous cell carcinoma, begins in the flat cells that line the tube, and it is the most common form of esophageal cancer worldwide. It is also the one associated with smoking and alcohol.

That distinction matters for what follows, because it is the second type, and only the second type, that keeps turning up in studies about hot drinks.

Why heat is suspected in the first place

The leading hypothesis is simple: a scalding liquid injures the cells lining the food pipe on its way down, and repeated injury opens the way to cancer. The study behind this week's headlines notes that these tumors typically arise from squamous cells in the upper two thirds of the esophagus, precisely the stretch most exposed to hot liquids.

Aaron Sasson, chief of surgical oncology at Stony Brook Cancer Center in New York, who was not involved in the research, described the mechanism to Fox News Digital by analogy with a skin burn: a burned area of the hand carries a higher risk of squamous cell carcinoma, and drinking very hot liquids amounts to "constantly repeating a burn to the esophagus." Ian Johnson, an epithelial physiologist and emeritus fellow at the Quadram Institute in England, told CNN by email that there is prior evidence that hot liquids damage those cells and cause inflammation, "so there is a plausible explanation for the findings."

None of this is new. In 2016 the International Agency for Research on Cancer, the World Health Organization's cancer agency, classified very hot drinks as "probably carcinogenic to humans" and "one probable cause of oesophageal cancer." The agency set the line for "very hot" at above 65 degrees Celsius. The evidence behind that classification came largely from studies in South America, Asia, Africa and the Middle East, where drinking tea or mate, a caffeinated herbal drink widely consumed in Argentina, Uruguay and southern Brazil, at or above 70 degrees was linked to higher risk.

That is the backdrop against which the new research arrives.

What the study measured: temperature, not the drink

Researchers at the University of Oxford analyzed data from 977,282 middle-aged adults in the United Kingdom, drawn from two long-running cohorts that routinely log participants' health, the Million Women Study and the UK Biobank. Participants in the first were followed for an average of 14 years, those in the second for 11. The work was published in the International Journal of Cancer and funded by Cancer Research UK.

The questions were blunt. People said whether they took their hot drinks "very hot," "hot" or "warm," or that they did not drink hot drinks at all, and whether they had fewer than six or six or more hot drinks a day. Roughly 15 percent said they liked their drinks very hot, and just under half reported six or more a day.

The central finding is that the association attached to the temperature, not to what was in the cup. The result held regardless of the type of drink, which the authors read as evidence that heat, rather than the composition of tea or coffee, is the risk factor at issue. Adding milk, a British habit that cools a cup slightly, did not change the picture either, as long as the drink was still hot.

The numbers behind the "triple risk"

Compared with people who drank their beverages warm, those who drank them hot had around 1.7 times the risk of squamous cell carcinoma, and those who drank them very hot around three times the risk, lead author Keren Papier, a senior nutritional epidemiologist at Oxford Population Health, told Fox News Digital. Frequency mattered on its own: after controlling for temperature, six or more hot drinks a day was associated with a 71 percent higher risk than fewer than six.

There was no evidence of any association between drink temperature and adenocarcinoma, the other form of the disease, in either cohort.

The researchers also put the finding in preventive terms. If the association reflects a genuine cause and effect, they estimate that about 14 percent of squamous cell cases in the UK, roughly 440 diagnoses a year, could be avoided if people who take their drinks very hot switched to merely hot. And because risk rose steadily across the temperature categories, the authors write that pushing consumption temperatures "well below average for this population may well avoid an even greater proportion" of cases.

Why this one is different

Papier has been explicit that the link itself is not novel. What is new is where the data come from. "This is currently the largest study to look at this question in a UK population, where many people consume tea and coffee daily," she said in a statement, adding that it "reinforces the existing evidence." Earlier work, she noted, was mostly carried out in South America, Asia and the Middle East, where drinking cultures differ. The authors describe the analysis as the largest and broadest on the subject to date.

In other words, the risk does not belong to mate gourds or to a specific Asian tea ritual. It showed up in a Western population whose daily routine is a kettle and a mug, and among people who are not going to give up breakfast.

The caveats the researchers make themselves

The biggest one is the study's own instrument. Nobody measured a single cup. Temperature was self-reported, and the team says it cannot determine how a person's "very hot" relates to an absolute temperature. The study also flags the limits of relying on fixed thresholds such as 65 degrees given real-world variability in thermal exposure, and notes that higher risk tends to appear alongside three other habits: burning your mouth more often, drinking faster, and waiting less time before the first sip.

Muy-Teck Teh, a professor of molecular oral oncology at Queen Mary University of London, said in a statement released through the Science Media Centre that because perceived temperature is subjective and participants' oral sensitivity is unknown, "the results should be interpreted as robust associations rather than causal proof." He raised a further possibility that cannot be excluded: that people who tolerate or prefer very hot drinks may have altered heat sensation or mucosal sensitivity that itself reflects an underlying biological predisposition to this cancer, which complicates any reading of causality. Papier said more research is needed to identify the exact drink temperatures linked to the increased risk.

A rare cancer, surrounded by bigger risks

A tripled relative risk sounds alarming until you see the baseline. Squamous cell esophageal cancer is rare, affecting a few thousand people a year in the UK, where esophageal cancer overall accounts for about 2 percent of cancer cases and carries roughly a 1 percent lifetime risk of diagnosis, according to Cancer Research UK. In the United States the lifetime risk of this specific subtype is under 1 percent, Sasson said, and about 85 percent of esophageal cancers there are adenocarcinomas, the type the study found no link to.

Papier said smoking remains the biggest risk factor for this form of cancer. Fiona Osgun, head of health information at Cancer Research UK, put it the same way: "The most important ways to reduce the risk of this cancer type are not smoking and cutting down on alcohol."

What to do with this information

The practical adjustment is not giving anything up. It is moving the first sip.

Water off a fully boiled kettle is at 100 degrees, and once poured into a cup it sits around 90 to 95, comfortably above the threshold the study is concerned with. Waiting a few minutes brings it down. Papier told CNN that for anyone worried by the findings, "a simple step is to let the drink cool down," by letting it sit, adding milk or cold water, blowing on it, or taking small sips. Osgun said it is hard to put an exact time on how long to wait, and suggested waiting "until it's comfortable to drink rather than drinking it while it's still very hot." Note the wrinkle there: heat tolerance varies from person to person, which makes comfort a rougher guide than it sounds.

Frequency is a separate lever. Because the 71 percent figure held after temperature was accounted for, staying under six hot drinks a day appears to matter on its own terms.

Two things the findings do not license. Cancer Research UK, which funded the study, does not believe cafés, coffee shops and restaurants should start serving tea and coffee cooler. And the heat of your cup is not the main item on the list. Johnson said he was inclined to take the research at face value and that it would be prudent to drink cooler beverages, "but whether people who favour hot drinks can change their habits so easily is another matter." Sasson was blunter about proportion: for most people, it is not the predominant risk factor, and limiting alcohol and eliminating cigarettes is what does "wonders for your esophagus."