Very hot tea can promote the development of esophageal cancer: anyone who regularly drinks more than 0.7 liters of tea at a temperature of at least 60 degrees, has a significantly increased risk of developing squamous cell carcinoma in the esophagus. This is the conclusion of an Iranian study led by Farhad Islami of the Tehran University of Medical Sciences in Tehran, which is featured in the International Journal of Cancer.
Evidence of such a relationship has been around for some time. In 2018, a research group at the University of Beijing found that, in addition to smokers, tea drinkers, in particular, are often affected by esophageal cancer.
Therefore, the International Agency for Research on Cancer (IARC) classifies “drinking very hot drinks at over 65 degrees Celsius” as “possibly carcinogenic”. The Cancer Information Service of the German Cancer Research Center (DKFZ) also warns against very hot drinks on its website in connection with esophageal cancer.
The researchers around Islami now present results on a very large database: For their investigation, they collected data from more than 50,000 women and men in the northern Iranian province of Golestan between 2004 and 2017. The participants were tracked on average for a good ten years. In addition to the exact circumstances of tea consumption, the researchers recorded socioeconomic data and dietary habits.
Trained employees visited the study participants in their apartments. To determine the preferred drinking temperature, two cups of tea were poured in each case. The employee put a thermometer into a cup. When the temperature of the tea had dropped to 75 degrees Celsius, participants were asked to drink the tea. If the tea was still too hot for them, they were asked again at 70, 65 and 60 degrees to drink it.
Altered genetic material due to inflammation
The preferred drinking temperature was noted. In previous studies, participants themselves reported how hot their tea is when they drink it – a procedure that prone to error.
During the study period, there were 317 cases of squamous cell carcinoma among the participants, one of the two most common types of esophageal cancer. After adjusting for possible other factors such as smoking or alcohol consumption, there were statistically clear relationships between the temperature of the tea and the risk of cancer. It goes without saying that the shorter the time between pouring and drinking with the respective tea drinker, the greater the risk of cancer.
As for the possible cause, the researchers write that the hot fluid can cause injury, resulting in inflammatory processes in the tissue of the esophagus. In turn, the genetic material can be changed directly or the formation of carcinogenic substances can be increased – with a tumor as a possible consequence.
Even Stephen Evans of the London School of Hygiene and Tropical Medicine, who was not involved in the study, suspected heat injuries as the cause. Also in the microwave heated jam is known to cause injury to the esophagus. “It is possible that the injury leads to cell changes and thus to cancer”.