Clinical Care/Education/Nutrition
Original Article

Antihyperglycemic Effect of Oolong Tea in Type 2 Diabetes

Kazuaki Hosoda, BS1, Ming-Fu Wang, PHD2, Mei-Ling Liao, MS2, Chin-Kuang Chuang, MD3, Miyuki Iha, BS4, Beverly Clevidence, PHD5 and Shigeru Yamamoto, PHD4
1 Research Center, Suntory, Osaka, Japan
2 Department of Food and Nutrition, Providence University, Taichung, Taiwan
3 Chorng Kuang Hospital, Miaoli, Taiwan
4 School of Medicine, University of Tokushima, Tokushima, Japan
5 Beltsville Human Nutrition Research Center, U.S. Department of Agriculture, Beltsville, Maryland

OBJECTIVE—To determine the efficacy of oolong tea for lowering plasma glucose in type 2 diabetic patients in Miaoli, Taiwan.

RESEARCH DESIGN AND METHODS—A total of 20 free-living subjects who had type 2 diabetes and took hyperglycemic drugs as prescribed were enrolled in the present study. Subjects consumed oolong tea (1,500 ml) or water for 30 days each in a randomized crossover design. Tea was not consumed for 14 days prior to treatments.

RESULTS—Relative to initial concentrations, oolong tea markedly lowered concentrations of plasma glucose (from 229 ± 53.9 to 162.2 ± 29.7 mg/dl, P < 0.001) and fructosamine (from 409.9 ± 96.1 to 323.3 ± 56.4 µmol/l, P < 0.01), whereas the water control group had not changed (208.7 ± 61.0 vs. 232.3 ± 63.1 mg/dl for glucose and from 368.4 ± 85.0 to 340.0 ± 76.1 µmol/l for fructosamine).

CONCLUSIONS—Oolong tea may be an effective adjunct to oral hypoglycemic agents in the treatment of type 2 diabetes.

Abbreviations: HPLC, high-performance liquid chromatography