Tea Consumption and Risk of Cancer: An Umbrella Review and Meta-Analysis of Observational Studies

Abstract

Tea is one of the most widely consumed beverages, but its association with cancer risk remains controversial and unclear. We performed an umbrella review to clarify and determine the associations between tea consumption and various types of cancer by summarizing and recalculating the existing meta-analyses. Meta-analyses of observational studies reporting associations between tea consumption and cancer risk were searched on PubMed and Embase. Associations found to be statistically significant were further classified into levels of evidence (convincing, suggestive, or weak), based on P value, between-study heterogeneity, prediction intervals, and small study effects. Sixty-four observational studies (case-control or cohort) corresponding to 154 effect sizes on the incidence of 25 types of cancer were included. Forty-three (27.9%) results in 15 different types of cancer were statistically significant. When combining all studies on the same type of cancer, 19 results in 11 different types of cancer showed significant associations with lower risk of gastrointestinal tract organ cancer (oral, gastric, colorectal, biliary tract, and liver cancer), breast cancer, and gynecological cancer (endometrial and ovarian cancer) as well as leukemia, lung cancer, and thyroid cancer. Only the reduced risk of oral cancer in tea-consuming populations (OR = 0.62; 95% CI: 0.55, 0.72; P value < 10−6) was supported by convincing evidence. Suggestive evidence was found for 6 results on biliary tract, breast, endometrial, liver, and oral cancer. To summarize, tea consumption was shown to have protective effects on some types of cancer, particularly oral cancer. More well-designed prospective studies are needed with consideration of other factors that can cause biases.

Validity of observational evidence on putative risk and protective factors: appraisal of 3744 meta-analyses on 57 topics

“…Fifty-seven umbrella reviews including 3744 associations assessed by meta-analyses of observational studies were included [ 5 , 6 , 27 – 81 ] (Fig. 2 and Table 2 ).…”

“…Meta-analyses of the proportions of convincing and highly suggestive associations across the 57 topics resulted in 1.3% (95% CI [1.0–2.2%]) summary proportion for convincing and 4.6% (95% CI [2.9–6.6%]) summary proportion for highly suggestive associations, and both had very high between-topic heterogeneity (I 2 = 73.9% and I 2 = 85.7%, respectively) (Table 3 and Additional file 2 : Figures 1 to 5). Convincing associations varied from 0 to 16.7% across topics and 29/57 umbrella reviews had no associations with convincing evidence [ 6 , 29 , 36 , 38 , 40 , 41 , 45 , 47 , 50 , 52 , 53 , 56 , 58 , 62 , 63 , 65 , 66 , 68 – 72 , 74 – 76 , 78 – 81 ] (Table 2 ). Moreover, the number of non-statistically significant associations (those with P≥0.05) varied substantially between topics from 0% for the associations of depression with mortality outcomes, antipsychotics with life-threatening events, and health factors with loneliness [ 40 , 55 , 68 ] to 80.7% for risk factors of prostate cancer [ 41 ].…”

Development and Validation of an Esophageal Squamous Cell Carcinoma Risk Prediction Model for Rural Chinese: Multicenter Cohort Study

“…Drinking tea is a very common and popular habit in China and is also a traditional way of leisure and entertainment. The relationship between tea drinking and cancer is still unclear while green tea is generally considered to be cancer resistant because it contains catechin or polyphenols ( 58 , 59 ). According to our study, preventive measures should be carried out for risk factors such as reducing alcohol drinking, reducing hot tea drinking, and keep proper weight.…”

Green Tea (Camellia sinensis) Extract Induces p53-Mediated Cytotoxicity and Inhibits Migration of Breast Cancer Cells

“…Evidence from case-control studies suggests that GT consumption may promote reduced incidence of breast cancer [ 8 , 9 ]. A recent umbrella review and meta-analysis of observational studies regarding tea consumption and risk of cancer showed that high consumption compared with low GT consumption significantly lowered the risk of breast cancer [ 10 ]. Further investigation is needed to provide evidence of the GT role in the overall risk of cancer [ 11 ].…”