Green tea intake and risk of incident kidney stones: Prospective cohort studies in middle-aged and elderly Chinese individuals.

Abstract

To investigate the association between green tea intake and incident stones in two large prospective cohorts. We examined self-reported incident kidney stone risk in the Shanghai Men's Health Study (n=58054; baseline age 40-74years) and the Shanghai Women's Health Study (n=69166; baseline age 40-70years). Information on the stone history and tea intake was collected by in-person surveys. Multivariable Cox proportional hazards models were adjusted for baseline demographic variables, medical history and dietary intakes including non-tea oxalate from a validated food frequency questionnaire. During 319211 and 696950 person-years of follow up, respectively, 1202 men and 1451 women reported incident stones. Approximately two-thirds of men and one-quarter of women were tea drinkers at baseline, of whom green tea was the primary type consumed (95% in men, 88% in women). Tea drinkers (men: hazard ratio 0.78, 95% confidence interval 0.69-0.88; women: hazard ratio 0.8, 95% confidence interval 0.77-0.98) and specifically green tea drinkers (men: hazard ratio 0.78, 95% confidence interval 0.69-0.88; women: hazard ratio 0.84, 95% confidence interval 0.74-0.95) had lower incident risk than never/former drinkers. Compared with never/former drinkers, a stronger dose-response trend was observed for the amount of dried tea leaf consumed/month by men (hazard ratiohighest category 0.67, 95% confidence interval 0.56-0.80, Ptrend <0.001) than by women (hazard ratiohighest category 0.87, 95% confidence interval 0.70-1.08, Ptrend =0.041). Green tea intake is associated with a lower risk of incident kidney stones, and the benefit is observed more strongly among men.