Dear Editor:
With great interest we read the article entitled “Tea consumption and risk of cancer: an umbrella review and meta-analysis of observational studies” by Kim et al. (1). Currently, a lot of misleading, unnecessary, and conflicted meta-analyses and systematic reviews have been published. Therefore, an umbrella review is needed to systematically collect and integrate data, evaluate information on all clinical outcomes, and provide an expanded view of the evidence (2, 3). We appreciate the efforts made by the authors to assess the epidemiological support for cancer outcomes being associated with tea consumption using an umbrella review. Previously, we conducted an umbrella review assessing the association between tea consumption and multiple health outcomes, in which we also assessed the cancer risk related to tea consumption (4).
In the present umbrella review, 64 observational studies with 25 types of cancer outcomes were included. In our previous umbrella review, 68 meta-analyses with 21 types of cancer outcomes were identified. In both umbrella reviews, high consumption of tea was related to reduced risks of biliary tract cancer, leukemia, oral cancer, ovarian cancer, and thyroid cancer, and when considering the types of tea, high consumption of green tea was associated with reduced risks of breast cancer, endometrial cancer, and liver cancer. Additionally, the present umbrella review by Kim et al. identified the protective role of tea against gastric cancer and lung cancer, and of green tea against colorectal cancer. However, only the negative association between tea consumption and risk of oral cancer was supported by convincing evidence. Our previous umbrella review also assessed the association between tea consumption and cancer mortality and found that consumption of black tea could reduce the risk of cancer mortality significantly (HR: 0.79; 95% CI: 0.65, 0.97) (5).
However, our previous umbrella review suggested that when the temperature of the tea consumed was >55–60°C, the associations become harmful for gastric (6) and esophageal cancer (7). Similarly, drinking very hot tea (>60°C) was significantly associated with an increased risk of esophageal cancer (HR: 1.62; 95% CI: 1.15, 2.22) from a cohort during an average 10 y of follow-up (8). The mechanism might be the impairment of barrier function of the esophageal epithelium by thermal injury, the inflammatory process associated with chronic irritation of the esophageal mucosa by hyperthermia, and mutations like higher rates of transitions of somatic G to A in CpG dinucleotides of the Tp53 gene, which were related to nitric oxide synthase activity (9).
In conclusion, although current evidence has suggested the protective role of tea for several cancers, we do not recommend that individuals consume very hot tea.
Notes
The authors reported no funding received for this study.
Author disclosures: The authors report no conflicts of interest.
Contributor Information
Mengshi Yi, Department of Hepatic Surgery, West China Hospital, Sichuan University, Chengdu, China.
Turun Song, Department of Urological Surgery, West China Hospital, Sichuan University, Chengdu, China.
Yong Zhou, Department of Gastrointestinal Surgery, West China Hospital, Sichuan University, Chengdu, China.
References
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