In general, drinking tea is a healthful habit. It beats drinking coffee, which although not harmful, does not convey any particular health benefits (as tea almost certainly does). But there is an important caveat, which was emphasized in a recent report in the British Medical Journal (now officially called by its initials, the BMJ). Drinking hot or very hot tea may make a certain type of esophageal cancer more likely to occur. Since the danger (almost certainly) comes from the damaging effect of heat per se, one should probably avoid all hot beverages and drink one's tea in a pleasantly warm state-perhaps cooled with milk, as the British often do.

Researchers chose Iran's northern Golestan province to examine this question. This is logical, since this province, located near the Caspian Sea, has one of the highest rates of esophageal cancer in the world. They looked in particular at squamous cell carcinoma of the esophagus, which has a particularly high rate of occurrence in this district of 1.7 million people.

Just about everyone in Golestan province drinks tea (Camilla sinensis). No surprise there. But researchers, headed by Farhad Islami of Tehran University, interviewed 300 people as well as 571 healthy people and controlled for other risk factors, including tobacco use. They asked study participants whether they drank their tea very hot, hot, warm, or lukewarm and also how long they let the tea brew before drinking it. This type of esophageal cancer turned out to be eight times as common among people who drank "very hot" tea, compared to warm or lukewarm tea drinkers. Islami established that in this community people 22 percent of people drank their tea at 65 degrees Celsius (= 149 degrees Fahrenheit) or higher. (This is normally the temperature of tea just after it is brewed.)

Is there something about drinks made from Camilla sinensis that is dangerous? Almost certainly not, since other tea drinking populations do not have similar rates of esophageal cancer. A major clue that is the same relationship between hot beverages, including a non-Camilla form of herbal tea called maté, and esophageal cancer is also seen in Argentina and Uruguay. Mate is a kind of "tea" that does not contain Camilla sinensis. As Islami noted, too-hot liquid could injure esophageal cells, paving the way for esophageal cancer. Islami's study is-in the words of the BMJ editorialists - "the most compelling test to date" of that theory. Even though the study was conducted in an unusual setting, "the findings are relevant to clinicians and researchers in many settings," according to an editorial that was published with the study.

The findings should be replicated, but letting hot drinks cool off for four or five minutes is a good idea, according to the editorialist David Whiteman, PhD, of Australia's Queensland Institute of Medical Research.

"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," Whitehead writes. Whitehead also says Islami's findings "are not cause for alarm... and should not reduce public enthusiasm for the time-honored ritual of drinking tea."

There is a political aspect to this study, as well. Given the difficult relations between the Iranian government and some other countries in the past, it is encouraging to see this cooperative activity between Iranian scientists and their colleagues in the West, with potential benefit for all people.

There is an informative video about this study at the BMJ Web site:
http://www.bmj.com/cgi/content/full/338/mar26_2/b610

--Ralph W. Moss, Ph.D.

References:

Islami F, Pourshams A, Nasrollahzadeh D, et al. Tea drinking habits and oesophageal cancer in a high risk area in northern Iran: population based case-control study. BMJ. 2009 Mar 26;338:b929. doi: 10.1136/bmj.b929.

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