Tea consumption and risk of type 2 diabetes: a longitudinal study with data from the Chinese Health and Nutrition Survey

Abstract Background Polyphenols identified in tea, such as catechins and epigallocatechin gallate, have been reported to be protective to diabetes in cell-based and animal studies. However, the association between tea consumption and incidence of type 2 diabetes in human beings is unclear. Our study aimed to assess the association between tea consumption and type 2 diabetes in people living in China, where tea is a commonly consumed beverage. Methods Participants were from the Chinese Health and Nutrition Survey, covering nine provinces (Heilongjiang, Liaoning, Shandong, Henan, Jiangsu, Hubei, Hunan, Guizhou, and Guangxi) of China. Our study included people aged at least 18 years who provided valid responses in the questionnaire with regards to tea consumption (n=12 771). Data for tea consumption and other participant characteristics were collected in 1997, 2000, 2004, 2006, and 2009, while data for incidence of self-reported type 2 diabetes was collected in 2000, 2004, 2006, 2009, and 2011. Interval-censored Cox regression with time-varying covariates was used to estimate the hazard ratio (HR) of tea consumption on incidence of type 2 diabetes. The HR was adjusted for age, sex, education level, smoking status, alcohol consumption, coffee consumption, physical activity, BMI, and hypertension. Findings Mean follow-up was 3·8 times over 8·5 years. 177 patients reported type 2 diabetes. At baseline, 8281 (65%) people drank no tea, 1 294 (10%) drank less than one cup (240 ml) per day, 1 054 (8%) drank one to two cups, and 2142 (17%) drank more than two cups. Compared with those who did not drink tea, those who drank less than one cup of tea per day had an adjusted HR for type 2 diabetes of 1·22 (95% CI 1·11–1·35), those who drank one to two cups had an adjusted HR of 1·35 (95% CI 1·23–1·49), and those who drank two or more cups had an adjusted HR of 1·39 (95% CI 1·30–1·48). Informed patient consent was given by all participants Interpretation Tea consumption was positively associated with risk of type 2 diabetes in Chinese adults. The main strength of the study was the multiple follow-ups on tea consumption, which allowed us to track the longitudinal changes among the participants. A major limitation was the self-reporting nature of the type 2 diabetes diagnosis. Further studies on the effects of tea constituents, other than polyphenols, on type 2 diabetes are warranted. Funding None.