March 26, 2009 -- Drinking hot or very hot tea may make a certain type of esophageal cancer more likely.
That news appears in the advance online edition of BMJ, formerly called the British Medical Journal.
Researchers studied tea drinkers in northern Iran's Golestan province, which has a high rate of esophageal squamous cell carcinoma.
That's the world's most common type of esophageal cancer. But it's not the type of esophageal cancer that's been rising in Western countries (that's adenocarcinoma of the esophagus).
Why study tea drinkers in northern Iran? Because just about everyone there drinks tea daily, and some esophageal cancer risk factors, like smoking tobacco and drinking alcohol, aren't common.
Hot Tea, Higher Risk
The Iranian tea study comes from researchers including Farhad Islami, a research fellow at Tehran University of Medical Sciences.
They interviewed 300 people with confirmed cases of esophageal squamous cell carcinoma, as well as 571 healthy people of similar backgrounds.
Participants answered questions about their tea-drinking habits, including how hot they usually drank their tea (very hot, hot, warm, or lukewarm) and how long they let the tea brew before drinking it.
Nearly all participants -- 98% -- said they drank black tea daily.
Esophageal cancer was eight times as common among people who drank "very hot" tea, compared to warm or lukewarm tea drinkers. By the same comparison, hot tea drinkers were twice as likely as warm or lukewarm tea drinkers to have esophageal cancer.
The findings held regardless of other risk factors. But what's "hot" to one person may be "lukewarm" to someone else.
So Islami's team checked data from more than 48,000 local people who were served tea and indicated their preferred tea temperature, which was checked by a digital thermometer.
The findings: 39% drank their tea at temperatures less than 60 degrees Celsius (140 degrees Fahrenheit), 39% drank their tea at 60-64 degrees Celsius (140-147 degrees Fahrenheit), and 22% drank their tea at 65 degrees Celsius (149 degrees Fahrenheit) or higher.
Cooling Off Period
Observational studies, like this one, don't prove cause and effect. So it's not certain that hot or very hot tea caused esophageal cancer, or whether all hot drinks might have the same effect.
The possible link between hot drinks and esophageal cancer risk isn't new.
"In South America, especially Argentina, there is a well established relationship between esophageal cancer and drinking very hot mate, a kind of tea which is usually consumed when it is almost boiling and is sipped through a metal spoon. The problem is not the tea but the chronic inflammation from drinking it hot," Michael Thun, MD, the American Cancer Society's vice president emeritus of epidemiology, tells WebMD via email.
Islami's team notes that too-hot liquid could injure esophageal cells, paving the way for esophageal cancer.
Islami's study is "the most compelling test to date" of that theory and even though the study was conducted in a unique setting, "the findings are relevant to clinicians and researchers in many settings," states an editorial published with the study.
The findings should be replicated, but letting hot drinks cool off for several minutes is a good idea, notes 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."