February 5, 2018

expert reaction to study investigating hot tea consumption, alcohol consumption, smoking, and oesophageal cancer in China

Researchers examined whether high-temperature tea drinking, along with the established risk factors of alcohol consumption and smoking, is associated with esophageal cancer risk, in a study, published in the Annals of Internal Medicine.

Prof. Jane Green, Professor of Epidemiology and Co-Director of the Cancer Epidemiology Unit, University of Oxford, said:

“This is an interesting and well-designed study which found that people in China who drink very hot tea may add to their risk of developing oesophageal cancer, but only in combination with other established risk factors such as smoking and alcohol drinking.  Due to this, I would treat the topline of the press release with caution as it might imply an exaggerated additional effect of hot tea consumption. In the ‘high risk’ group- those who drink moderate to high amounts of alcohol and also smoke, so are already at higher risk of oesophageal cancer- drinking hot tea daily about doubled their risk, taking the risk relative to non-drinkers and non-smokers from about 2.5 to 5.

“The implications for the UK are not clear. The results of this study apply only to the type of oesophageal cancer most common in China, squamous cell carcinoma. In the UK, Europe and USA, the most common type is adenocarcinoma, which is associated with different risk factors (mainly, smoking, obesity and acid reflux). This study does not tell us whether drinking hot tea is associated with risk of adenocarcinoma of the oesophagus. People in the UK also rarely drink tea as hot as that described in this study. Hot drinks may increase risk simply by damaging the cells lining the gullet, making them more susceptible to other risk factors, and it is probably wise to avoid anything which might do this- but this study does not mean that most people should stop drinking tea.”

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

“There are two points to make about this research. The first is that in China, a particular form of oesophageal cancer is prevalent- squamous cell carcinoma. In this study, 92% of the cases were oesophageal squamous cell carcinoma. In the West, this form is less prevalent and the predominant form of cancer is oesophageal adenocarcinoma, and hence the causes and risk factors are likely to be different.

“Secondly, we tend to drink tea at lower temperatures in the West than in China which is less damaging to the oesophagus. So, although the study might be relevant to populations in the China, it is less relevant in the West in terms of a causative factor. That said, there may be individuals out there who do drink very hot tea (with excessive alcohol and tobacco consumption as well) and hence might be more at risk of developing this cancer.

“As an aside, I found the paper’s final conclusions somewhat interesting in that it suggests that heavy drinkers of alcohol should abstain from hot tea drinking. Considering the impact of alcohol on health, perhaps that advice should be the other way round.”

Prof. Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“This is a very large and generally well-conducted study, but it seems unlikely to be very relevant to average tea drinkers in the UK. Mainly that’s because it seems to be more common in China than in the UK to drink really, really hot tea, what this research describes as ‘burning hot’. In the UK most people seem not to drink their tea nearly that hot, and it would be difficult to get it that hot if you put milk in it, as many people do here. If you do frequently drink extremely hot tea, maybe this study should persuade you that it might be worth reconsidering that habit – but you’d probably do a lot more to reduce your risk of oesophageal cancer by giving up smoking and not drinking too much alcohol.

“Like almost all studies of possible harmful health effects of some habit, such as drinking hot tea, this one is observational. That is, the researchers did not go out and make the participants drink hot tea. Instead, they recorded what the participants said about their tea drinking habits, and also recorded whether they later got oesophageal cancer. The trouble with this kind of study is that there might be some other factor, perhaps something else that the hot tea drinkers choose to eat or drink, that is the real cause of the cancer, and not the hot tea at all. The idea that very hot drinks might increase one’s chances of oesophageal cancer isn’t new, but almost all previous studies have compared people with and without oesophageal cancers, looking back into the past to see what their tea drinking habits were, whereas this one first asked about tea drinking, and then followed up nearly half a million people for several years to see which of them later developed the cancer in question. So-called prospective studies like this are less prone to bias than those that look back in time.

“However, that does not get over the possibility that something else than drinking hot tea is the real cause of the cancers. It’s possible to allow statistically for certain differences (other than tea drinking) between the people involved, and the scale of this study meant that the researchers could make several of these allowances. That still doesn’t solve the problem of what causes what entirely, but it helps. In particular the researchers looked at whether drinking alcohol, smoking cigarettes, or both, affected the correlation between hot tea drinking and oesophageal cancer. What they found was very interesting. For people who drank less than 15g of alcohol a day (that’s about 2 UK units) and who did not smoke, drinking really hot tea had rather little effect on their chances of getting oesophageal cancer. For people who drank more than that, particularly if they also smoked, the risk of oesophageal cancer did go up quite rapidly depending on how hot they drank their tea. The ‘5-fold increased risk … in high-risk individuals’, referred to in the top line of the press release, is the estimate from this study of the change in risk for people who drink more than 15g of alcohol a day, if they drink burning hot tea daily, compared to those who drink tea less than once a week, after allowing for differences in smoking habits and several other possibly relevant variables. So it’s a very specific comparison. Even for people who drink this amount of alcohol, drinking tea daily that was simply ‘warm’ did not increase the oesophageal cancer risk by a statistically significant amount. It seems to be only the ‘hot’, and particularly the ‘burning hot’, daily tea that has a clear effect on oesophageal cancer risk.

“In any case, these specific numbers are unlikely to apply exactly in the UK. Here, oesophageal cancer is considerably less common than in China, and the relationships between drinking very hot tea, drinking alcohol, and smoking may well be rather different in detail. The study can’t show that really hot tea is definitely a cause of oesophageal cancer, but it could be, so to be on the safe side, if you do drink really hot tea, you might want to think again about that.”

* ‘Effect of Hot Tea Consumption and Its Interactions With Alcohol and Tobacco Use on the Risk for Esophageal Cancer’ by Yu et al. published in The Annals of Internal Medicine on Monday 5 February.

Declared interests

Prof. Kevin McConway: Is a member of the SMC’s advisory board.