Journal
NUTRITION RESEARCH
Volume 33, Issue 3, Pages 180-187Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.nutres.2012.12.010
Keywords
Green tea; Antioxidants; Glutathione; Copper; Iron; Metabolic syndrome
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Funding
- University of Oklahoma Health Sciences Center General Clinical Research Center, National Center for Research Resources, National Institutes of Health [M01-RR14467]
- Oklahoma State University
- National Institutes of Health from the COBRE Program of the National Center for Research Resources [P20 RR 024215]
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Green tea, a popular polyphenol-containing beverage, has been shown to alleviate clinical features of the metabolic syndrome. However, its effects in endogenous antioxidant biomarkers are not clearly understood. Thus, we tested the hypothesis that green tea supplementation will upregulate antioxidant parameters (enzymatic and nonenzymatic) in adults with the metabolic syndrome. Thirty-five obese participants with the metabolic syndrome were randomly assigned to receive one of the following for 8 weeks: green tea (4 cups per day), control (4 cups water per day), or green tea extract (2 capsules and 4 cups water per day). Blood samples and dietary information were collected at baseline (0 week) and 8 weeks of the study. Circulating carotenoids (alpha-carotene, beta-carotene, lycopene) and tocopherols (alpha-tocopherol, gamma-tocopherol) and trace elements were measured using high-performance liquid chromatography and inductively coupled plasma mass spectroscopy, respectively. Serum antioxidant enzymes (glutathione peroxidase, glutathione, catalase) and plasma antioxidant capacity were measured spectrophotometrically. Green tea beverage and green tea extract significantly increased plasma antioxidant capacity (1.5 to 2.3 mu mol/L and 1.2 to 2.5 mu mol/L, respectively; P < .05) and whole blood glutathione (1783 to 2395 mu g/g hemoglobin and 1905 to 2751 mu g/g hemoglobin, respectively; P < .05) vs controls at 8 weeks. No effects were noted in serum levels of carotenoids and tocopherols and glutathione peroxidase and catalase activities. Green tea extract significantly reduced plasma iron vs baseline (128 to 92 mu g/dL, P < .02), whereas copper, zinc, and selenium were not affected. These results support the hypothesis that green tea may provide antioxidant protection in the metabolic syndrome. (C) 2013 Elsevier Inc. All rights reserved.
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