Tea Drinking and Risk of Cancer Incidence: A Meta-Analysis of Prospective Cohort Studies and Evidence Evaluation.

Here we provide a comprehensive meta-analysis to summarize and appraise the quality of the current evidence on the associations of tea drinking in relation to cancer risk. PubMed, Embase, and the Cochrane Database of Systematic Reviews were searched up to June 2020. We reanalyzed the individual prospective studies focused on associations between tea drinking and cancer risk in humans. We conducted a meta-analysis of prospective studies and provided the highest- versus lowest-category analyses, dose-response analyses, and test of nonlinearity of each association by modeling restricted cubic spline regression for each type of tea. We graded the evidence based on the summary effect size, its 95% confidence interval, 95% prediction interval, the extent of heterogeneity, evidence of small-study effects, and excess significance bias. We identified 113 individual studies investigating the associations between tea drinking and 26 cancer sites including 153,598 cancer cases. We assessed 12 associations for the intake of black tea with cancer risk and 26 associations each for the intake of green tea and total tea with cancer risk. Except for an association between lymphoid neoplasms with green tea, we did not find consistent associations for the highest versus lowest categories and dose-response analyses for any cancer. When grading current evidence for each association (number of studies ≥2), weak evidence was detected for lymphoid neoplasm (green tea), glioma (total tea, per 1 cup), bladder cancer (total tea, per 1 cup), and gastric and esophageal cancer (tea, per 1 cup). This review of prospective studies provides little evidence to support the hypothesis that tea drinking is associated with cancer risk. More well-designed studies are still needed to identify associations between tea intake and rare cancers.

Coffee drinking and cancer risk: an umbrella review of meta-analyses of observational studies.

BACKGROUND: Epidemiological studies on the association between coffee intake and cancer risk have yielded inconsistent results. To summarize and appraise the quality of the current evidence, we conducted an umbrella review of existing findings from meta-analyses of observational studies. METHODS: We searched PubMed, Embase, Web of Science and the Cochrane database to obtain systematic reviews and meta-analyses of associations between coffee intake and cancer incidence. For each association, we estimated the summary effect size using the fixed- and random-effects model, the 95% confidence interval, and the 95% prediction interval. We also assessed heterogeneity, evidence of small-study effects, and excess significance bias. RESULTS: Twenty-eight individual meta-analyses including 36 summary associations for 26 cancer sites were retrieved for this umbrella review. A total of 17 meta-analyses were significant at P ≤ 0.05 in the random-effects model. For the highest versus lowest categories, 4 of 26 associations had a more stringent P value (P ≤ 10- 6). Associations for five cancers were significant in dose-response analyses. Most studies (69%) showed low heterogeneity (I2 ≤ 50%). Three and six associations had evidence of excessive significance bias and publication bias, respectively. Coffee intake was inversely related to the risk of liver cancer and endometrial cancer and was characterized by dose-response relationships. There were no substantial changes when we restricted analyses to meta-analysis of cohort studies. CONCLUSIONS: There is highly suggestive evidence for an inverse association between coffee intake and risk of liver and endometrial cancer. Further research is needed to provide more robust evidence for cancer at other sites.