Hot tea can promote the development of esophageal cancer. Those who regularly drink more than 0.7 liters of tea per day at a temperature of at least 60 degrees have a significantly increased risk of developing a tumor in the esophagus. This is the conclusion of a recent study published in the International Journal of Cancer.
Evidence of such a relationship has been around for some time. The World Health Organization (WHO) had already classified "drinking very hot drinks at more than 65 degrees Celsius" in 2016 as "possibly carcinogenic". The investigation referred to tea as well as coffee or cocoa. The German Cancer Research Center (DKFZ) also warns against very hot drinks in connection with esophageal cancer.
The results of the current study complement these estimates with a very large database: For their research, researchers collected information from more than 50,000 women and men in the northern Iranian province of Golestan between 2004 and 2017. On average, the scientists accompanied the participants for ten years.
In addition to the exact habits of tea consumption, researchers collected data on education and household income, as well as dietary habits, which may also affect cancer risk.
Home visits to determine the serving temperature
Employees also visited the study participants in their homes to determine the tea's preferred drinking temperature. For this, they had the men and women each pour two cups. The employee put a thermometer into a cup. When the temperature of the tea had dropped to 75 degrees Celsius, the participants were first asked to sip.
If the tea was still too hot for them, researchers started at 70, 65 and 60 degrees each further experiments until the drink had reached the preferred drinking temperature. In previous studies, participants themselves reported how hot their tea is when they drink it - a relatively error-prone procedure.
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In the course of the study, 317 of the 50,000 participants developed squamous cell carcinoma, one of the two most common forms of esophageal cancer. After taking into account other possible influencing factors such as smoking or alcohol consumption, there were statistically clear relationships between the temperature of the tea and the risk of cancer, the researchers report.
The conclusion is that the shorter the time between pouring and drinking, the greater was the risk of cancer, the researchers report by Farhad Islami of the Tehran University of Medical Sciences in Tehran (Iran).
Compared to participants who consumed less than 0.7 liters of tea per day at a temperature of less than 60 degrees, the risk of cancer increased by 90 percent for those who consumed more tea at a higher temperature.
However, according to the DKFZ, esophageal cancer is a relatively rare disease in Germany. In 2014, a malignant tumor of the esophagus was detected in 5370 men and 1560 women.
How could hot drinks promote cancer?
The researchers assume that the hot fluid causes injuries that could set off inflammatory processes. These in turn could alter the genome or promote the formation of carcinogenic substances - 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 injury due to heat as a cause. "It's possible that the injury leads to cell changes and thus to cancer," he says.
This direct connection, however, can not prove the current study one hundred percent, their only drawback: The data can only show that lovers of hot teas are more likely to develop cancer - but not that the hot tea has actually caused the tumors.
According to the DKFZ, smoking, alcohol and chronic heartburn increase the risk of esophageal cancer in addition to very hot tea.