Daily higher tea consumption is associated with a reduced risk of type 2 diabetes: A cohort study and updated systematic review and meta-analysis

Tea is abundant in phytochemicals (such as polyphenols and theaflavins), which have a hypoglycemic effect. Previous studies investigating the relationship between tea consumption and the risk of type 2 diabetes mellitus (T2DM) have yielded inconsistent results. We hypothesized that tea consumption would be associated with a reduced risk of T2DM. This cohort study used data from the China Health and Nutrition Survey, involving a total of 5199 participants initially recruited in 1997 and subsequently followed until 2009. Consumption of any variety of tea was tracked using structured questionnaires, and T2DM was diagnosed according to the American Diabetes Association's criteria. We also performed a systematic literature search of PubMed, Web of Science, and EMBASE for publications through September 2021, including 19 cohort studies comprising 1,076,311 participants. In our cohort study, the logistic regression model showed a relative risk (RR) of T2DM among tea drinkers of 1.02 (95% confidence interval [CI], 0.82-1.28) compared with non-tea drinkers. Although our updated meta-analysis showed no significant association between tea consumption and T2DM on the whole (pooled RR of 0.96 [0.91-1.00]), compared with the non-tea-drinking group, participants consuming 4 or more cups of tea per day had a 17% reduced risk of T2DM, with an RR of 0.83 (95% CI, 0.76-0.90). These data support our hypothesis that tea consumption at higher doses (e.g., ≥4 cups/day) is associated with a reduced risk of T2DM.