Aims Acute administration of oolong tea decreases blood glucose levels. We investigated the association between long-term oolong tea intake and subsequent risk of developing diabetes among men of working age. Methods Data were analysed from a cohort of participants in the High-risk and Population Strategy for Occupational Health Promotion Study (HIPOP-OHP), conducted in Japan from 1999 to 2004. Oolong tea intake at baseline and subsequent risk of diabetes was evaluated using a Cox proportional hazards model. Results Of 4975 male workers, a total of 201 cases of diabetes were reported over a median of 3.4years of follow-up. Mean age and BMI of all participants at baseline were 38.3years and 22.9kg/m 2, respectively. Compared with those not consuming oolong tea, multivariable adjusted hazard ratios for developing diabetes were 1.00 (95%CI 0.67-1.49) for those who drank one cup of oolong tea per day and 1.64 (95%CI 1.11-2.40) for those drinking two or more cups per day. Fasting blood glucose increment per year was 0.11mmol/l (95%CI 0.09-0.12mmol/l), 0.12mmol/l (95%CI 0.09-0.15mmol/l) and 0.15mmol/l (95%CI 0.11-0.18mmol/l), respectively, for oolong tea consumption of 0, 1 and ≥2cups/day, with a significant linear trend (P<0.0001). Conclusions Long-term consumption of oolong tea may be a predictive factor for new onset diabetes. Further studies are necessary to elucidate the role of oolong tea in the risk of developing diabetes.
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