Antihyperglycemic Effect of Oolong Tea in Type 2 Diabetes

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


    • Address correspondence and reprint requests to Shigeru Yamamoto, PhD, Applied Nutrition Laboratory, Department of Nutrition, School of Medicine, the University of Tokushima, 3 Kuramoto, Tokushima City 770-8503, Japan. E-mail: syamamoto{at}

      Received for publication 24 November 2002 and accepted in revised form 4 March 2003.

      A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

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