April 3, 2009 — Drinking hot tea was strongly associated with a higher risk for esophageal cancer according to the results of a northern Iranian population-based case-control study reported online first on March 27 in the British Medical Journal.
"An association between drinking hot beverages and risk of oesophageal cancer has been reported in several studies from different parts of the world," write Farhad Islami, MD, from Shariati Hospital, Tehran University of Medical Sciences in Iran, and colleagues. "In Golestan, tea and water are the only drinks commonly consumed, with comparable average intake. An ecological study showed that inhabitants of Golestan drank more tea and at a higher temperature than people living in a nearby area with a low incidence of oesophageal cancer."
The goal of this study was to evaluate the relationship between characteristics of tea drinking habits in Golestan province in northern Iran, which is an area with a high incidence of esophageal squamous cell carcinoma (SCC), and risk for that disease. Patterns of tea drinking and temperature at which tea was usually drunk were also determined for healthy persons enrolled in a cohort study.
Tea drinking among 300 patients with histologically proven esophageal SCC was compared with that in 571 matched neighborhood controls in the case-control study and in 48,582 participants in the cohort study. The primary study endpoint was the odds ratio (OR) of esophageal SCC associated with drinking hot tea.
Regular drinking of black tea was reported by 98% of the cohort participants, with mean daily volume more than 1 L. Reported temperature of tea was less than 60°C in 39.0% of participants, 60°C to 64°C in 38.9%, and 65°C or higher in 22.0%. Reported temperature agreed moderately with actual temperature measurements (weighted κ, 0.49).
In the case-control study, risk for esophageal cancer was increased for drinking hot tea (OR, 2.07; 95% confidence interval [CI], 1.28 – 3.35) or very hot tea (OR, 8.16; 95% CI, 3.93 – 16.9) vs lukewarm or warm tea. Risk was also significantly increased for drinking tea 2 to 3 minutes after pouring (OR, 2.49; 95% CI, 1.62 – 3.83) or less than 2 minutes after pouring (OR, 5.41; 95% CI, 2.63 – 11.1) vs drinking tea at least 4 minutes after being poured. Responses to the questions about temperature at which tea was drunk agreed strongly with interval from tea being poured to being drunk (weighted κ, 0.68).
"Drinking hot tea, a habit common in Golestan province, was strongly associated with a higher risk of oesophageal cancer," the study authors write.
Limitations of this study include possible information bias regarding the amount and temperature of consumed tea, validation study performed among healthy people, possible selection bias, and some missing data.
"A large proportion of Golestan inhabitants drink hot tea, so this habit may account for a substantial proportion of the cases of oesophageal cancer in this population," the study authors write. "Informing the population about the hazards of drinking hot tea may be helpful in reducing the incidence of oesophageal cancer in Golestan and in other high risk populations where similar habits are prevalent."
In an accompanying editorial, David C, Whiteman, from Queensland Institute of Medical Research at Royal Brisbane Hospital in Australia, recommends allowing tea to cool for 5 minutes before drinking.
"The mechanism through which heat promotes the development of tumours warrants further exploration and might be given renewed impetus on the basis of these findings," Dr. Whiteman writes. "These findings are not cause for alarm, however, and they should not reduce public enthusiasm for the time honoured ritual of drinking tea. Rather, we should follow the advice … [that suggests] a five to 10 minute interval between making and pouring tea, by which time the tea will be sufficiently flavoursome and unlikely to cause thermal injury."
The Digestive Disease Research Center of Tehran University of Medical Sciences, the National Cancer Institute, National Institutes of Health, and the International Agency for Research on Cancer supported this study. The study authors and Dr. Whiteman have disclosed no relevant financial relationships.
BMJ. Published online March 27, 2009.
http://www.medscape.com/viewarticle/590589?sssdmh=dm1.454091&src=nldne
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