August 29, 2022

expert reaction to observational study on black tea consumption and mortality

An observational study published in Annals of Internal Medicine uses data from UK Biobank to look at tea consumption and mortality.

Prof Fernando Rodríguez Artalejo, Professor of Preventive Medicine and Public Health at the Autonomous University of Madrid, CIBERESP and IMDEA-Food, said:

“This article shows that regular consumption of black tea (the most widely consumed tea in Europe) is associated with a modest reduction in total and, especially, cardiovascular disease mortality over 10 years in a middle-aged, mostly white, adult general population. It represents a substantial advance in the field, both in terms of the rigour of its methods and the paucity of information previously available; most studies had been done in Asia (where green tea is the most widely consumed) and the few outside Asia were small in size and inconclusive in their results.  

“Like any observational epidemiological study, this one does not definitively establish that tea is the cause of the lower mortality of tea drinkers; this is because it cannot exclude that the lower mortality is due to other health factors associated with tea consumption (so-called “confounders”). Theoretically, the best way to clarify this question is to have a large clinical trial where tea consumption is randomised between two or more groups of subjects, who would be followed over time to see if mortality is reduced in those who consume tea (or specific amounts of tea). Such a study would be very costly and has many practical difficulties, as it is not easy to recruit many people who would agree to drink tea or not as the researchers propose, and who would do so for years. Therefore, the simplest short-term approach is to explore the possibility of a “Mendelian randomisation” study, which is an observational design that can demonstrate causal associations under certain conditions: this design would compare mortality in people who have genetic variants that a) influence higher or lower tea consumption, b) are not related to potential confounders, and c) only influence mortality through tea consumption.

“On the other hand, it is desirable that studies similar to this one are conducted in the future only in people with cardiovascular disease, mainly ischaemic heart disease or atrial fibrillation, to ensure that in them the caffeine in tea is safe and that regular tea consumption brings some benefits. Finally, for those of us who do not consume tea on a regular basis, the relevant question (which this study does not answer) is whether starting to consume tea would improve our health. To do this, studies should be done with repeated measurements of tea consumption over time and compare the mortality of those who do not consume tea on a sustained basis with that of those who have started to consume tea or have increased their consumption over time, and those who have been drinking tea for years.”

‘Tea Consumption and All-Cause and Cause-Specific Mortality in the UK Biobank’ by Maki Inoue-Choi et al. et al. was published in Annals of Internal Medicine at 22:00 UK time on Monday 29^th August.

DOI: 10.7326/M22-0041

Declared interests

Prof Fernando Rodríguez Artalejo: “No conflicts of interest.”