A study carried out in a province of northern Iran where people drink lots of hot tea every day found there was a strong link between drinking very
hot tea and a higher risk of cancer of the oesophagus, the tube of muscle that carries food from the throat to the stomach.
The study was the work of Dr Reza Malekzadeh, professor and director of the Digestive Disease Research Center of Shariati Hospital at the Tehran University of Medical Sciences, and colleagues, and was published online on 26 March in the British Medical Journal, BMJ.
The researchers suggest people wait a few minutes before drinking tea made with boiling water, since they concluded that drinking very hot tea (that is at or above 70 degrees C or 158 degrees Fahrenheit) can raise a person's risk of developing cancer of the oesophagus.
However, in an accompanying editorial, David Whiteman of the Queensland Institute of Medical Research in Australia said there was no cause for alarm and advised people always to let hot food and drinks cool a little before swallowing them.
Oesophagal cancers, of which OSCC (oesophageal squamous cell carcinoma) is the most common, kill half a million people worldwide every year. Tobacco and alcohol use is the most common cause in Europe and America and is more likely to affect men than women, however, a tendency to consume hot drinks is also thought to play a role.
For the study, researchers went to Golestan Province in northern Iran because it has one of the highest rates of OSCC in the world, but women are just as likely to get it as men, and the numbers of people who smoke and drink alcohol are quite low. On the other hand, lots of people drink hot tea.
Malekzadeh and colleagues recruited 300 patients diagnosed with OSCC and matched them with 571 healthy people from the same area (the controls). Nearly all the participants in both groups were regular tea drinkers, consuming on average over a litre a day.
They asked them questions about how hot they drank their tea and how long they waited after pouring it before starting to drink it.
The researchers then measured the actual temperature that nearly 50,000 people from the same area drank their tea at and compared it to the participants' description. The temperature ranged from under 60 to over 70 degrees C, and the researchers found that what the participants described as the temperature agreed moderately with actual measurements.
The results showed that:
- Compared with drinking warm or lukewarm tea (65 deg C or less), drinking hot tea (65 to 69 deg C) was linked to a doubling of the risk of OSCC.
- Drinking very hot tea (70 deg C or more) however, was linked to an eight-fold increased risk of OSCC.
- Drinking tea within two minutes of pouring it was linked with a five-fold higher risk of OSCC compared to drinking it after four minutes.
- There was no link between how much tea people drank and risk of OSCC.
"Drinking hot tea, a habit common in Golestan province, was strongly associated with a higher risk of oesophageal cancer."
UK studies show that healthy people tend to report drinking tea at around 56 to 60 deg C.
The researchers said it was probably worth telling the people of Golestan and other high risk populations with similar drinking habits about the health risk of having very hot drinks.
These findings are consistent with the idea that thermal injury may cause epithelial cancers, said Whiteman, though he pointed out that the underlying mechanism is not clear and should be studied further.
However, Whiteman said people should not alarm themselves about these findings and hopes public enthusiasm for drinking tea is not diminished: just let food and drinks cool from "scalding" to "tolerable" before swallowing them, he said.
"Tea drinking habits and oesophageal cancer in a high risk area in northern Iran: population based case-control study."
Farhad Islami, Akram Pourshams, Dariush Nasrollahzadeh, Farin Kamangar, Saman Fahimi, Ramin Shakeri, Behnoush Abedi-Ardekani, Shahin Merat, Homayoon Vahedi, Shahryar Semnani, Christian C Abnet, Paul Brennan, Henrik Møller, Farrokh Saidi, Sanford M Dawsey, Reza Malekzadeh, Paolo Boffetta.
BMJ 2009, 338:b929
Published online 26 March 2009
Written by: Catharine Paddock, PhD