Tea consumption and risk of type 2 diabetes: a dose-response meta-analysis of cohort studies

Tea consumption has inconsistently been shown to be associated with the risk of type 2 diabetes (T2D). The aim of the present study was to conduct a dose-response meta-analysis of cohort studies assessing the association between consumption of tea and risk of developing T2D. Pertinent studies were identified by searching PubMed, Web of Science and EMBASE through 31 March 2013. A total of sixteen cohorts from fifteen articles that reported 37,445 cases of diabetes among 545,517 participants were included. A significant linearly inverse association between tea consumption and T2D risk was found (P for linear trend = 0.02). An increase of 2 cups/d in tea consumption was found to be associated with a 4.6 (95% CI 0.9, 8.1) % reduced risk of T2D. On the basis of the dose-response meta-analysis, the predicted relative risks of diabetes for 0, 1, 2, 3, 4, 5 and 6 cups of tea consumed per d were 1.00 (referent), 0.97 (95% CI 0.94, 1.01), 0.95(95% CI 0.92, 0.98), 0.93 (95% CI 0.88, 0.98), 0.90 (95% CI 0.85, 0.96), 0.88 (95 % CI 0.83, 0.93) and 0.85 (95% CI 0.80, 0.91), respectively. There was a statistically significant heterogeneity within the selected studies (Q= 45.32, P< 0.001, I 2= 60.3 %). No evidence of substantial small-study bias was found (P= 0·46). Our findings suggest that tea consumption could be linearly inversely associated with T2D risk. Future well-designed observational studies that account for different characteristics of tea such as tea types, preparation methods and tea strength are needed to fully characterise such an association.