Drinking very hot tea may increase the risk of throat cancer, according to Iranian doctors who say knowing about the link could help prevent cases.

Golestan Province in northern Iran has one of the highest rates of esophageal squamous cell carcinoma, a type of throat cancer.

'These findings are not cause for alarm, however, and they should not reduce public enthusiasm for the time honoured ritual of drinking tea.'— David Whiteman

In Europe and North America, it is caused mainly by smoking and drinking alcohol and is more common in men than women, but drinking hot beverages could also be a factor in the tumours.

To investigate, Prof. Reza Malekzadeh of Tehran University of Medical Sciences and colleagues studied the tea-drinking habits of 300 people with esophageal cancer and 571 healthy men and women from Golestan.

Nearly all of the participants drank black tea regularly, consuming an average of more than a litre a day, researchers said in this week's British Medical Journal.

But smoking and alcohol consumption rates were low, limiting a factor that complicated previous attempts to research the topic.

Study participants who regularly gulped down their tea less than two minutes after pouring were five times more likely to develop the cancer compared with those who waited four or more minutes, the team said.

Hazards of hot tea

Likewise, compared with drinking warm or lukewarm tea (65 C or less), drinking hot tea (65-69 C) was linked with twice the risk of esophageal cancer, and drinking very hot tea (70 C or more) was associated with an eight-fold increased risk.

The researchers measured the temperature of the tea consumed by nearly 50,000 residents.

"Informing the population about the hazards of drinking hot tea may be helpful in reducing the incidence of esophageal cancer in Golestan and in other high risk populations where similar habits are prevalent," the team concluded.

British studies have reported people prefer to drink their tea at an average temperature of 56 C to 60 C in healthy populations.

The findings lend support to the idea that thermal injury to the lining of the throat somehow sets up cancer, the researchers said.

Wait for flavour

Cancers of the esophagus kill more than 500,000 people worldwide each year, mostly in discrete populations in Asia, Africa and South America.

The tumours are especially deadly, with five-year survival rates of 12 to 31 per cent.

There was no association between the amount of tea consumed and the risk of cancer.

Hot beverages are consumed worldwide, though perhaps not at the scalding temperatures seen in Iran, David Whiteman from the Queensland Institute of Medical Research in Australia said in an editorial accompanying the study.

It's possible thermal injury may be behind some of the cases of esophageal squamous cell carcinoma elsewhere, he said.

"It is difficult to imagine any adverse consequences of waiting at least four minutes before drinking a cup of freshly boiled tea, or more generally allowing foods and beverages to cool from 'scalding' to 'tolerable' before swallowing," Whiteman wrote.

"These findings are not cause for alarm, however, and they should not reduce public enthusiasm for the time-honoured ritual of drinking tea."

Rather, tea connoisseurs should follow the advice of English cookbook author Mrs. Beeton, who suggested waiting five to 10 minutes between making and pouring tea to allow it to be flavoursome and unlikely to cause thermal injury.