March 20, 2019

expert reaction to research on hot tea and oesophageal cancer

Research published in the International Journal of Cancer claims to strengthen the existing evidence supporting an association between hot beverage drinking and esophageal cancer.

Prof Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine (LSHTM), said:

“This is basically good observational research. The prior measurements of tea temperature and the follow-up for cancer have been done well. The numbers of cases of oesophageal cancer are sufficiently high to detect real effects if they exist. The conclusion- “As there is no known health benefit from drinking very hot beverages, it will be reasonable to advise people in Golestan (Iran) and elsewhere to wait for their hot beverages to cool down before drinking” is reasonably justified. It is possible that the magnitude of the effect may have been exaggerated slightly, but it is also possible that the effect has been underestimated. The fact that virtually all the adjusted estimates are notably less than the unadjusted suggests that there may be unmeasured factors that would reduce the estimates further. These effects have generally been shown by studies in other countries as well as previous research in Iran.

“Tea is the only drink consumed in the area, so the data relate to this beverage. It is also true that in this area of Iran, that tea is frequently drunk at high temperatures.  They did not study any other drink, but other studies have, and it seems that it is the heat that is the issue rather than the actual beverage.  In fact, it is probably anything hot: microwaved jam has been known to cause oesophageal injury.  It is possible that the trauma leads to cell changes and hence to cancer. The paper goes through various possible mechanisms, but this paper does not show what mechanism is responsible.

“The data certainly suggest that 60C is a threshold and this has been shown in some animal studies quoted.  I am not an expert in UK tea temperature, but in Iran they do not add milk generally, while in the UK many do add cold milk which reduces the temperature dramatically. Based on the current research, as the authors say, there is no merit in drinking very hot beverages, so to avoid the extremes is a reasonable precaution.

“The authors have adjusted for quite a number of other factors such as age, sex, wealth, cigarette smoking (very important factor), but there could be others not measured and adjustment for them might reduce the magnitude of effects seen.

“The authors, unfortunately and not following best practice, do not give the absolute or absolute excess risk. They do say there are 317 cases over the median follow-up of just over 10 years (503,865 person years. If we take this rate it is about 63 cases per 100,000 person-years among the entire cohort, including tea drinkers at varying temperatures and non-tea drinkers. If the extra risk of 1.42 for those drinking tea at >60C is applied to these figures then the excess is about 17 cases per 100,000 person years.

“Perhaps this very small absolute risk is why the authors did not quote it. That region of Iran has high rates of oesophageal cancer and hot tea drinking is a contributor to that rate. In the UK the rate overall is about 14 per 100,000 per year, but this varies dramatically by age and also by sex. Males at ages over 80 have a rate about 100 per 100,000 per year and females at that age have about 60 per 100,000. At ages below 50 the rate for males is below 10 and for females below 2 per 100,000. {ref: https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/oesophageal-cancer}.

“It can be seen that all these risks are very low, and for an individual have very little impact, but across a country with high rates of oesophageal cancer, the overall impact is potentially important. It is less important in the UK, both because of lower rates of oesophageal cancer and because of the likely different approach to drinking hot beverages.

“This is definitely not a ‘scare’ story when placed in the wider context, but avoidance of extremely hot drinks will have no adverse and possibly beneficial health effects.”

Dr James Doidge, Senior Research Associate, University College London (UCL), said:

“This is valuable research but not a ground-breaking discovery. Hot drinks are an established risk factor for oesophageal cancer and it doesn’t take a scientist to appreciate that repeated irritation of any body surface increases your risk of cancer. Sunburn gives us skin cancer, smoking gives us lung cancer, and many foods and drinks contribute to risk of gastrointestinal cancers.

“Let’s put the statistics into perspective: in the UK, about one in fifty men and one in one hundred women will be diagnosed with oesophageal cancer at some point in their lives, most commonly in their eighties. About 34% of cases have been attributed to smoking, 27% to obesity and 13% to alcohol. Hot beverages probably lie nearer the lower end of this range because Britons usually prefer their tea with milk and at a lower temperature of 56-60 degrees, but better understanding this risk is no doubt why Cancer Research UK contributed to this study’s funding. However, if you enjoy your tea piping hot and we take the results on this study on face value, then we are talking about an additional lifetime risk of oesophageal cancer of around one in one hundred for a lifetime of drinking hot tea. Not an insubstantial risk but one that should be balanced against the pleasure that you personally derive from your daily ritual, the unknown but probably smaller gains that you would get from changing your habit now, and the fact that if you don’t develop oesophageal cancer then something else will surely be along to fill that role sooner or later. And by focusing on the more general risk factors of smoking, obesity and alcohol, you can lower your risk of a whole range of cancers at once!”

Dr Bing Hu, Associate Professor in Oral and Dental Health Research at the University of Plymouth:

“I would say there is some overspeculation here. Any hot foods/liquid can induce cell damages, it is not only linked with tea. It is well known that temperatures higher than 60 degrees are harmful for keratinocytes – which produce keratin, the key structural protein that makes up the outer layer of human skin. In addition, this study only analysed 317 new ESCC cases that occurred from 50,045 individuals, which represents a very small portion of the total volume.

“There are a couple of other factors have not been considered such as the link between specific tea subtype (not only black or green tea) and daily time of consumption (very important for linking with saliva). Saliva has a vital protection and diluting role, particularly in relation to harmful environments such as sour tastes and hot temperatures, and saliva component and secretion rates differ a lot during a day and between individuals.”

Prof Andrew Sharrocks, Professor of Molecular Biology, University of Manchester, said:

Overall, the data in this study add to the growing literature that has linked drinking hot tea to getting a particular subtype of oesophageal cancer- squamous cell carcinoma. There is a clear association between drinking very hot beverages (here defined above 65 degrees) and the chances of getting oesophageal squamous cell carcinoma. It is advisable therefore to allow drinks to cool before drinking them, although adding cold milk as is often the case in western societies would produce the same effect. Indeed, the incidence of this type of cancer is a lot lower in western countries, which may partly reflect these drinking habits.

Prof Jessica Corner FMedSci, Pro-Vice-Chancellor (Research & Knowledge Exchange) at The University of Nottingham, said:

“It is a useful study, remember this is in the context of many many epidemiological studies of all kinds of behaviours and exposures that can increase cancer risk so that we need to put it in perspective and not encourage mass abandonment of tea drinking! The question about hot coffee or other beverages you would imagine would be the same – though no studies probably.

“It is conducted in the context of a particular cultural context where hot, black tea is a common drink. We should consider studies in a UK context that would also include other beverages.”

Background/context on the subject:

Prof Mel Greaves, Director of the Centre for Evolution and Cancer at The Institute of Cancer Research, said:

“The finding in a large, prospective cohort study of a link between oesophageal cancer and drinking hot tea is credible. It adds to long standing epidemiological data that have associated consumption of hot beverages with geographic ‘hot spots’: regions of the world with increased risk of that cancer. These include very hot tea in Central Asia, hot Calvados in France and hot maté in parts of South America.

“It isn’t clear why or how hot liquid has this apparent effect. Possibilities include direct damage to the oesophageal lining cells, another that hot liquid functions, in smokers, as a solvent for cigarette tar, washing chemical carcinogens down the oesophagus. As smoking is a recognised risk factor for oesophageal cancer both mechanisms could play a part, interacting to increase risk in the case of smokers who’ like it hot’.”

‘A prospective study of tea drinking temperature and risk of esophageal squamous cell carcinoma’ by Farhad Islami et al. was published in the International Journal of Cancer at 4:01am UK TIME on Wednesday 20 March 2019.

All our previous output on this subject can be seen at this weblink: http://www.sciencemediacentre.org/expert-reaction-to-study-investigating-hot-tea-consumption-alcohol-consumption-smoking-and-oesophageal-cancer-in-china/

Declared interests

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