• Kang Chen, Dong Chen, Chuangxin Lan, Xiongfa Liang, Tao Zeng, Jian Huang, Xiaolu Duan, Zhenzhen Kong, Shujue Li, Hans-Göran Tiselius, Alberto Gurioli, Xiaogang Lu, Guohua Zeng, and Wenqi Wu.
• Department of Urology, Minimally Invasive Surgery Center, The First Affiliated Hospital of Guangzhou Medical University, Guangdong Key Laboratory of Urology, Kangda Road 1#, Haizhu District, Guangzhou, 510230, Guangdong, China.
• Int Urol Nephrol. 2018 Jan 1; 50 (1): 29-33.

ObjectiveTo investigate the impact of green tea on urinary oxalate excretion in healthy male volunteers.Materials And MethodsThe oxalate concentrations after different brewing times (2-60 min) of different qualities (2-8 g) of green tea were measured in in vitro experiment. In in vivo experiment, the effects on urine composition were assessed in 12 healthy men with an age of 24-29 years. Each subject was requested to collect two 24-h urine samples under normal dietary conditions. Green tea prepared from tea bags containing 2 g of tea leafs was consumed by the subjects for 7 consecutive days, and 24-h urine samples were collected and analyzed on days 6 and 7. After 3-week washout interval, all subjects consumed green tea containing 4 g of leaf tea for another 7 consecutive days. Two 24-h urine samples were collected on the last 2 days. Urine volume, pH, calcium, magnesium, sodium, phosphate, potassium, chloride, citrate, oxalate, urate and creatinine were measured.ResultsIn the in vitro experiments, oxalate in solution increased with brewing time (p < 0.05) and tea quality (p < 0.05). In the in vivo experiment, 24-h urinary oxalate increased significantly (0.24 ± 0.09 mmol to 0.32 ± 0.13 mmol, p = 0.045) when tea was prepared from 2-g bags of green leaf tea. Consumption of green tea containing 4 g of leaf tea resulted in 24-h urinary oxalate increase (0.25 ± 0.25 mmol to 0.34 ± 0.22 mmol, p = 0.041).ConclusionsIn vitro studies showed that there was a gradual increase in solution concentrations of oxalate that was associated with increased brewing time and increased quality of green tea. Studies in normal men showed that green tea consumption was associated with increased urinary exertion of oxalate.

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