Tea Study Reveals Unexpected Risks Due to Drinking "Very Hot Beverages"

The way you take your tea feels like a matter of life or death. Some like sugar, others take it with milk, while some prefer artificial sweeteners that could alter the microbiome. Temperature is a key factor, too: If you take it excruciatingly hot, the results of a new International Journal of Cancer study has some sobering news to report.

This study on 50,045 individuals from the Northeast Region of Iran found strong ties between drinking at least 700 milliliters of tea beyond 60 degrees Celsius (140 degrees Fahrenheit) per day and an esophageal cancer called a squamous cell carcinoma.

That type of cancer typically infects the cells that line the upper and middle sections of esophagus and only made up one percent of new cancer cases in the United States in 2018. Drinking a lot of very hot tea on a regular basis, the authors reports, increased the risk of esophageal cancer in their study population by 90 percent. 

Dr. Farhard Islami, the strategic director of Cancer Surveillance Research at the American Cancer Society, says the results really boil down to temperature, not beverage choice.

“Many people enjoy drinking tea, coffee, or other hot beverages,” he said. “However, according to our report, drinking very hot tea can increase the risk of esophageal cancer, and it is therefore advisable to wait until hot beverages cool down before drinking.”

Islami’s pattern may seem strange, but hot beverages are already on the the cancer risk radar. The International Agency for Research on Cancer actually classifies “drinking very hot beverages above 65 degrees Celsius” as “probably carcinogenic,” which places it in its second tier of risky activities alongside inorganic lead compounds, consumption of red meat, and “shift work that involves circadian disruption.” The top tier includes factors like tobacco and solar radiation.

Islami’s paper shows very strong evidence that the link between hot drink and cancer is closer than we realized. In this study, the authors went above and beyond to document every aspect of their participants’ tea drinking habits to establish correlations with their health. This is remarkable for many reasons, not least because 50,045 people were involved in the research.

First, each of the participants filled out a survey including questions about how long they usually let tea sit before they drank it, and whether they liked their tea warm, hot, or very hot. Then, the researchers actually brewed tea in front of them until it was 75 degrees Celsius (that’s quite hot). If the participant drank the tea and said that it seemed about right or even cooler than their preferred tea temperature, they stopped the experiment there. If the person preferred tea cooler, they allowed the tea to cool until they found it palatable. Then, they followed up with their participants for over ten years.

The actual number of people who developed esophageal cancer was low — only 317 of over 50,000. But the tea-drinking preferences and patterns of those 317 people, in the context of the total study population, were enough to suggest a strong correlation between drinking hot tea and cancer risk. Importantly, however, the results do not prove causation — only a robust link.

People who preferred “very hot” tea had more than double the risk of developing esophageal cancer than those who preferred cold or lukewarm tea, the team reports. Those who drank tea above 60 degrees Celsius, meanwhile, had a 41 percent higher risk of developing esophageal cancer than those who let it cool down below that temperature. Taking their statistics together, the authors arrived at their final figure: a 90 percent increase in risk in people who drank at least 700 milliliters of tea hotter than 60 degrees Celsius (140 degrees Fahrenheit).

There’s no official guidance yet on how people should be taking their tea (and other hot drinks), but the link to esophageal cancer described in this study was enough to make Islami offer caution to tea drinkers. Until we know for sure, it might be worth taking the heat of a hot beverage down a notch. A bit of patience — and even just a cool breeze — could go a long way.

Abstract: Previous studies have reported an association between hot tea drinking and risk of esophageal cancer, but no study has examined this association using prospectively and objectively measured tea drinking temperature. We examined the association of tea drinking temperature, measured both objectively and subjectively at study baseline, with future risk of esophageal squamous cell carcinoma (ESCC) in a prospective study. We measured tea drinking temperature using validated methods and collected data on several other tea drinking habits and potential confounders of interest at baseline in the Golestan Cohort Study, a population‐based prospective study of 50,045 individuals aged 40–75 years, established in 2004–2008 in northeastern Iran. Study participants were followed‐up for a median duration of 10.1 years (505,865 person‐years). During 2004–2017, 317 new cases of ESCC were identified. The objectively measured tea temperature (HR 1.41, 95% CI 1.10–1.81; for ≥60°C vs. <60°C), reported preference for very hot tea drinking (HR 2.41, 95% CI 1.27–4.56; for “very hot” vs. “cold/lukewarm”), and reported shorter time from pouring tea to drinking (HR 1.51, 95% CI 1.01–2.26; for <2 vs. ≥6 min) were all associated with ESCC risk. In analysis of the combined effects of measured temperature and amount, compared to those who drank less than 700 ml of tea/day at <60°C, drinking 700 mL/day or more at a higher‐temperature (≥60°C) was consistently associated with an about 90% increase in ESCC risk. Our results substantially strengthen the existing evidence supporting an association between hot beverage drinking and ESCC.