In a study published in the British Medical Journal, scientists in Iran have found that drinking black tea at temperatures higher than 70 degrees centigrade can increase the risk of oesophageal cancer. Experts think that this could be one explanation for the increased rates of this cancer in developing countries.
In the West, most people add milk to their tea, dropping the temperature significantly.
Oesophagus cancers kill more than 500 000 people worldwide each year and oesophageal squamous cell carcinoma (OSCC) is the most common type.
Tobacco and alcohol are the main factors linked to the development of oesophageal cancers in Europe and America.
But it has not been clear why other populations around the world have high rates of the disease although there has been a theory that regularly drinking very hot drinks damages the lining of the gullet.
Golestan Province in northern Iran has one of the highest rates of OSCC in the world, but rates of smoking and alcohol consumption are low and women are as likely to have a diagnosis as men. Tea drinking, however, is widespread.
The University of Tehran researchers studied tea drinking habits among 300 people diagnosed with OSCC and compared them with a group of 570 people from the same area.
Nearly all participants drank black tea regularly, on average drinking over a litre a day.
Compared with drinking warm or lukewarm tea (65 degrees C or less), drinking hot tea (65-69 degrees C) was associated with twice the risk of oesophageal cancer, and drinking very hot tea (70 degrees C or more) was associated with an eight-fold increased risk.
The speed with which people drank their tea was also important.
Drinking a cup of tea in under two minutes straight after it was poured was associated with a five-fold higher risk of cancer compared with drinking tea four or more minutes after being poured.
