Is "piping hot" dangerous? Insights from a study of about 1 million people on esophageal cancer risk and the real reason to let your food cool

Is "piping hot" dangerous? Insights from a study of about 1 million people on esophageal cancer risk and the real reason to let your food cool

The Shocking "3 Times Risk with Hot Drinks"

Morning coffee, tea during work breaks, tea after meals. A steaming cup is a daily ritual for many to switch gears. However, a large-scale study suggesting a link between the "heat" of these drinks and a type of esophageal cancer has been published, drawing attention with the figure "3 times the risk."

The study was led by Dr. Keren Papier and her team at Oxford University, with the results published in the medical journal 'International Journal of Cancer.' The analysis involved 977,282 adults participating in the UK Biobank and Million Women Study. Using approximately 14 years of follow-up data, the study examined the relationship between preferences and consumption of hot drinks and the incidence of esophageal cancer.

To summarize the conclusion, what needs attention is not the type of beverage like "coffee" or "tea," but the habit of repeatedly drinking them at temperatures so hot they could burn the mouth or throat. However, it is incorrect to simplistically conclude that "drinking hot beverages causes esophageal cancer" or that "exceeding 65°C once is dangerous." The study indicates a statistical correlation within a population, not a prediction of individual fate.


The 3.17 Times Increase Was Not for All Esophageal Cancers

Esophageal cancer is broadly divided into "esophageal squamous cell carcinoma," arising from the squamous cells lining the esophagus, and "esophageal adenocarcinoma," arising from glandular cells. In this study, a clear association with the heat of beverages was observed only with the former.

Compared to those who described their drinks as "warm," those who described them as "very hot" had a 3.17 times higher relative risk of esophageal squamous cell carcinoma. The 95% confidence interval was 2.49–4.03, and the association remained even after adjusting for factors like consumption frequency. On the other hand, a similar association was hardly observed with esophageal adenocarcinoma.

Furthermore, in analyses considering beverage temperature, those who drank six or more cups of hot drinks a day had a 71% higher risk of esophageal squamous cell carcinoma compared to those who drank fewer than six cups. This suggests that not only "how hot" but also "how frequently the esophagus is exposed to heat" might be important.

The research team estimated that about one in seven cases of esophageal squamous cell carcinoma in the UK could potentially be prevented if people who prefer very hot drinks switched to a lower "hot" level. However, this is a preventable proportion calculated from group data and does not guarantee the same effect for everyone.


Why Heat Might Lead to Cancer

The proposed mechanism is relatively straightforward. Repeated damage to the esophageal mucosa by high-temperature liquids can lead to repeated inflammation and repair. During this process, DNA damage and abnormal cell proliferation may occur more easily, making cells more susceptible to the effects of carcinogens.

The International Agency for Research on Cancer (IARC), a specialized cancer agency of the World Health Organization, classified "very hot beverages" as probably carcinogenic to humans (Group 2A) in 2016. IARC's "very hot" refers to temperatures exceeding 65°C. Studies in regions like China, Iran, Turkey, and South America, where tea or mate is consumed at around 70°C, have shown a tendency for esophageal cancer to increase with higher temperatures.

It is important not to misunderstand that IARC's classification is not a ranking of "how dangerous" something is, but an evaluation of "how much evidence there is for carcinogenic potential." Moreover, IARC classifies coffee itself as Group 3, meaning it cannot be classified as carcinogenic. The current topic is more about the physical irritation from heat rather than the components of coffee or tea being dangerous.


"65°C" Is Not a Measured Threshold in This Study

The figure of 65°C has been prominently featured in reports, but it requires careful interpretation. In the Oxford study, the temperature of each participant's cup was not measured with a thermometer. Participants self-reported their preference as "very hot," "hot," "warm," or "do not drink hot beverages."

Therefore, it cannot be strictly rephrased that the 3.17 times result applies to "those who drank above 65°C." The 65°C is an international guideline by IARC and may not completely align with the self-reported categories in this study. The perception of heat can vary among individuals, and factors like the material of the cup, quantity, room temperature, and whether milk is added can affect how quickly a drink cools.

It is also important to note that this is an observational study. Researchers have statistically adjusted for many factors like smoking, alcohol consumption, and socioeconomic status, but cannot completely rule out the influence of unmeasured lifestyle habits. Additionally, people who prefer "very hot" drinks might have a dulled sense of heat or different mucosal properties, so it has not been proven that hot drinks alone are the cause.

Nevertheless, the large scale of nearly 980,000 subjects, the long follow-up period, the trend of higher risk with higher temperature categories, and consistency with previous studies worldwide make it difficult to explain the findings as mere coincidence. While acknowledging the study's limitations, there is ample value in paying attention to temperature as an avoidable risk.


Before Being Shocked by "3 Times," Consider Absolute Risk

The most easily misunderstood aspect of health news is the difference between relative risk and absolute risk. Hearing "3 times" might give the impression that one in three people will get cancer. However, if the original incidence rate is low, even a threefold relative increase means the individual's absolute probability remains low.

The lifetime risk of developing esophageal squamous cell carcinoma in the UK is reported to be about 1%. While it cannot be simply converted to "1% will definitely become 3%," it is clear that the figure of 3.17 times should not be overly feared. On the other hand, esophageal cancer can be asymptomatic in its early stages and have a poor prognosis. Therefore, adopting preventive measures that impose little daily burden makes sense.

It is also important not to forget the prioritization of major risk factors. Particularly for esophageal squamous cell carcinoma, smoking and heavy alcohol consumption are significant risk factors. Focusing only on hot drinks while continuing to smoke or drink excessively is not the right order for prevention. Avoiding heat is not a substitute for quitting smoking or reducing alcohol but a small habit to add to them.


Questions Spread on Social Media—"So, How Long Should I Wait?"

In public posts on Facebook and other platforms introducing this news, practical questions such as "Is it the coffee or the temperature that's bad?" "What temperature is safe?" and "How many minutes should I let it cool after brewing?" came to the forefront. There were also voices concerned about the combination with smoking or drinking, and cautious reactions questioning whether causal relationships can be drawn from self-reported temperatures.

These reactions reflect a lack of information on how to incorporate the strong headline "3 times" into daily life. Some people may become anxious, thinking "I can't drink tea anymore," while others may scoff at the news, saying "everything causes cancer." However, what the study conveys is not to stop drinking beverages, but to reconsider the habit of enduring the heat.

Posts and comments on social media are not opinion polls and do not represent the overall picture of reactions. Moreover, in short texts, "association" can easily be replaced with "cause," and "specific cancer" with "all cancers." In this topic, at least the following three points should be shared together.

First, the association was mainly shown with esophageal squamous cell carcinoma. Second, 3.17 times is a relative risk, and the absolute risk is low. Third, the study did not measure beverage temperature, and 65°C is an IARC guideline. If these three points are missing, the cautionary message can turn into unnecessary fear.


So, How Should You Drink?

Expert advice is simple. Rather than setting a waiting time in seconds, "wait until you can drink comfortably without feeling heat or pain in your mouth or throat." Do not immediately put your mouth on a cup filled with boiling water; let it sit until the steam subsides a bit. Stirring, removing the lid, transferring to another container, or adding cold milk if you like can also lower the temperature.

It is also important not to use "it's hot but bearable" as a safety standard. People accustomed to hot drinks might allow high temperatures based solely on their own perception. While it is not necessary to use a thermometer daily, those concerned can measure their usual drinking temperature at home once to check for discrepancies with their perception.

Moreover, if you experience difficulty swallowing, a feeling of food sticking, unexplained weight loss, pain in the chest or throat, or prolonged hoarseness, consult a medical institution instead of self-diagnosing as "probably due to hot drinks." Preventive information and decisions about seeking medical attention for symptoms should be considered separately.


Don't Give Up Your Cup, Just Take a Breath

This study does not make daily coffee or tea an enemy. Rather, its value lies in highlighting risk factors that can be changed while preserving enjoyment. Place the cup down, enjoy the aroma, and take a sip after it has cooled a bit. If that short time reduces heat stimulation to the esophagus, it becomes a preventive measure that requires no cost or special tools.

Scientifically, there are still points to verify, such as exactly from what temperature the risk increases, how many minutes to wait, and how temperature and frequency interact. Nonetheless, the judgment of "not repeatedly drinking at a heat that could cause burns" aligns with existing international knowledge.

Rather than remembering only the shocking "3 times," it is important to understand the study's subject, limitations, absolute risk, and other major factors. It is not necessary to give up your cherished cup. Just wait a little longer for the first sip.

※This article is intended for general informational purposes and is not a substitute for individual diagnosis or treatment.


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