Date: 4/2/2009
TUMSPR News: In an article published by the British Medical Journal (BMJ) in late March 2009, TUMS researchers conclude that allowing tea to cool for five minutes before drinking would be safer.
In a paper published by British Medical Journal (BMJ) on March 26, 2009, researchers conclude that allowing tea to cool for five minutes before drinking would be safer.
According to the editorials and the paper published in BMJ, Dr. Islami, Dr. Malekzadeh and their colleagues from Tehran University of Medical Sciences (TUMS) at GI Diseases Research Center in Iran and researchers from other institutions in England, France, Sweden and USA assess the association between the way people drink their tea and the risk of esophageal squamous cell carcinoma.
Cancers of the esophagus, the tube that connects mouth to stomach, kill more than 500,000 people worldwide each year, with the bulk of the disease occurring in discrete populations in Asia, Africa, and South America.
Despite recent increases in the incidence of adenocarcinomas of the esophagus in industrialized nations, the most common subtype of esophageal cancer worldwide is esophageal squamous cell carcinoma. Tobacco and alcohol are the main causal factors related to esophageal squamous cell carcinoma in the West, but they are not implicated in non-Western populations that have very high rates of this disease. Nutritional deficiency, viral infection and dietary toxins have all been postulated as causal factors, although none can fully explain the extraordinary excess of cases of esophageal squamous cell carcinoma seen in these populations.
An intriguing hypothesis is that repeated thermal injury to the esophageal epithelium may initiate carcinogenesis, but the limited evidence to date is inconclusive. Previous studies have indicated that consuming hot maté (a South American herbal beverage) or hot alcoholic liqueurs increases the risk of esophageal squamous cell carcinoma.
However, testing this hypothesis has been hampered by the difficulty of separating the effect of heat from the confounding effects of ingested products already known or thought to cause this cancer (alcohol, tobacco, and maté). A further challenge has been to obtain valid and reliable estimates of the temperature at which participants typically swallow food or beverages, because all studies have relied on self-reports of intake.
Islami and his colleagues study is the most compelling test to date of the thermal injury hypothesis for esophageal squamous cell carcinoma in humans. The study was conducted in a population in northern Iran with a high incidence of the disease. The investigators first elicited the tea drinking preferences of 300 people with esophageal squamous cell carcinoma and a matched group of 571 controls drawn from the same geographical area. When compared with cancer-free controls, the patients were more than twice as likely to report drinking their tea "hot" (Odds ratio=2.07 and 95% confidence interval of 1.28 to 3.35) rather than “warm or lukewarm” and were eight times more likely to drink their tea "very hot" (OR=8.16, CI= 3.93 to 16.9). The findings were similar for rapidity of intake — people who drank their tea within two minutes had a five-time higher risk than those who waited more than four minutes before drinking their tea. These are substantial increases in the relative risk of cancer, and although observational studies are prone to well-known forms of bias, the investigators minimized methodological error as much as possible.
An important potential weakness was that the estimates of tea drinking temperature were based on self-reports by the participants. To tackle this problem — and in an attempt to calibrate the reports of warm, hot, and very hot tea — the investigators conducted a second study in which they measured the actual temperature of the tea consumed by nearly 50,000 residents of the same province of Iran. Taken together, these studies provide persuasive evidence that drinking tea at temperatures greater that 70ºC markedly increases the risk of esophageal squamous cell carcinoma.
Strengths of the study include the high rates of case ascertainment and control participation, which lessen the chance that biased selection of study participants introduced systematic errors. In addition, the almost universal consumption of tea in this population, coupled with the low rates of exposure to tobacco and alcohol, greatly reduces the likelihood of confounding that has bedeviled earlier studies. Therefore, although this study was conducted in a population with atypical and possibly unique patterns of exposure to substances that are commonly consumed, the findings are relevant to clinicians and researchers in many settings.
At the level of basic science, this report lends support to the notion that thermal injury may be a cause of epithelial cancers. The mechanism through which heat promotes the development of tumors warrants further exploration and might be given renewed impetus based on these findings.
Given that randomized trials are unlikely to be conducted, any health advice must rely on these types of observational data. Replication of these findings is therefore desirable, but in the meantime, a precautionary approach should be taken in the region in which the study was conducted. Indeed, the consumption of hot drinks is common worldwide, although perhaps not at the scalding temperatures seen in Iran. It is therefore possible that thermal injury may underlie, at least in part, a proportion of cases of esophageal squamous cell carcinoma elsewhere. 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. These findings are not cause for alarm, however, and they should not reduce public enthusiasm for the time-honored ritual of drinking tea. Rather, we should follow the advice of Mrs. Beeton, who prescribes a five to 10 minute interval between making and pouring tea, by which time the tea will be sufficiently flavorsome and unlikely to cause thermal injury.
Earlier this week, U.S. and Japanese researchers reported that about a third of East Asians -- Chinese, Japanese and Koreans -- have an enzyme deficiency that puts them at higher risk of developing esophageal cancer when they drink alcohol3.
Reza Malekzadeh and other authors of this population based case-control study talk about the effect of tea drinking and esophageal cancer in Golestan province, northern Iran in this movie accessible through the following link:
http://www.mfreeth.com/movies/5.html
Picture Gallery
http://publicrelations.tums.ac.ir/gallery/detail.asp?galleryID=526
Rapid responses
Rapid responses have been posted to this article, which you can access through this link:
http://bmj.com/cgi/content/full/338/mar26_2/b929#responses
You can respond to this article at:
http://bmj.com/cgi/eletter-submit/338/mar26_2/b929
Researchers participating in the study:
Farhad Islami, research fellow (1,2,3), Akram Pourshams, associate professor(1), Dariush Nasrollahzadeh, PhD student(1,4), Farin Kamangar, research fellow(5), Saman Fahimi, PhD student(1,6), Ramin Shakeri, research fellow(1), Behnoush Abedi-Ardekani, pathologist(1), Shahin Merat, associate professor(1), Homayoon Vahedi, associate professor(1), Shahryar Semnani, associate professor and director(7), Christian C Abnet, investigator(5), Paul Brennan, group head(2), Henrik Møller, professor and director(3), Farrokh Saidi, professor(1), Sanford M Dawsey, senior investigator(5), Reza Malekzadeh, professor and director(1), Paolo Boffetta, group head and cluster coordinator(2)
1 Digestive Disease Research Center, Shariati Hospital, Tehran University of Medical Sciences, 14117 Tehran, Iran, 2 International Agency for Research on Cancer, Lyon, France, 3 King’s College London, Thames Cancer Registry, London, 4 Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden, 5 Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA, 6 Department of Public Health and Primary Care, Institute of Public Health, University of Cambridge, Cambridge, 7 Golestan Research Center of Gastroenterology and Hepatology, Gorgan University of Medical Sciences, Gorgan, Iran
References:
1- BMJ 2009;338:b610
2- Tea drinking habits and oesophageal cancer in a high risk area in northern Iran: population based case-control study:
http://www.bmj.com/cgi/content/full/338/mar26_2/b929?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Tea+drinking+habits&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
3- Reuters, Michael Kahn, Fri Mar 27, 2009 - Drinking hot tea may cause throat cancer
http://publicrelations.tums.ac.ir/english/news/detail.asp?newsID=1123
No comments:
Post a Comment