Hot tea is again linked to esophageal cancer Original paper

While animal and in vitro studies suggest that tea and its polyphenols may inhibit tumor formation and growth,^[1] observational human studies looking at the potential link between tea intake and cancer have produced mixed results, with some of the studies even linking tea intake to a higher risk of esophageal cancer.

These inconsistent results may be due to various confounding factors, notably drinking temperature. A 2019 prospective study we summarized here found that, compared to drinking tea colder than 60°C (140°F), drinking tea hotter than 60°C was associated with a 40% higher risk of esophageal cancer.^[2] This time, the study we’re summarizing is a meta-analysis.

This meta-analysis of 12 case-control studies totaling 5,253 cases and 8,273 controls looked for an association between esophageal cancer risk and hot-tea drinking. Subgroup analyses were based on tea intake (hot tea vs. no tea), tea temperature (hot vs. warm), tea type (green vs. others), cancer type (esophageal carcinoma vs. esophageal squamous-cell carcinoma), study region (China vs. others), and year of study publication (2000–2010 vs. 2011–2020).

The studies were conducted in China (9), Iran (1), Kenya (1), and Eastern Turkey (1). The types of tea consumed, in the studies that provided this information, were green tea (5 studies), black tea (1 study), and oolong tea (1 study).

Compared to drinking no tea or warm tea (including lukewarm), drinking hot tea (including very hot) was associated with a twofold increase in esophageal cancer risk.

There was no heterogeneity in this analysis, and the association remained statistically significant in all subgroups. The results did not materially change in the sensitivity analysis, either. Finally, there was no evidence of publication bias, and the methodological quality was high in 10 of the 12 studies.

All 12 studies included in the meta-analysis were case-control studies, which are vulnerable to selection bias (where individuals selected as controls are unrepresentative of the population that produced the cases) and recall bias (where individuals in the case group are more likely to recall a certain risk factor — in this case, hot-tea drinking — relative to individuals in the control group).

The present meta-analysis linked hot tea to a twofold higher risk of esophageal cancer. Similarly, two 2015 meta-analyses linked hot food/beverages to an almost twofold higher risk of esophageal cancer.^[3][4]

How might hot tea be carcinogenic?

One potential explanation is that chronic thermal irritation of the membrane that lines the esophagus might stimulate the formation of reactive nitrogen species (ROS), such as nitric oxide, and subsequently of carcinogenic N-nitroso compounds.^[5] Consistent with this idea, higher rates of mutations of the TP53 gene have been reported in samples of esophageal tumors collected in geographical areas where drinking hot beverages is considered an important risk factor for esophageal cancer.^[6][7] The TP53 gene provides instructions for making a tumor-suppressor protein, and mutations in this gene have been associated with nitric oxide synthase (NOS) activity.^[8]

Another potential explanation is that hot food and beverages may damage the membrane that lines the esophagus. This damage could impair the barrier function of the esophageal epithelium, thereby increasing the risk of harm from exposure to carcinogenic substances, such as alcohol and tobacco.^[9]