Applied nutritional investigationGreen tea minimally affects biomarkers of inflammation in obese subjects with metabolic syndrome
Introduction
A growing body of evidence indicates the role of green tea or its bioactive polyphenol, epigallocatechin gallate (EGCG), in significantly ameliorating features of metabolic syndrome, and subsequent risks for type 2 diabetes mellitus and cardiovascular disease (CVD) [1], [2], [3]. Metabolic syndrome, a constellation of several risk factors, including abdominal adiposity, hypertension, dyslipidemia [high triglycerides, low high-density lipoproteins (HDL)], and impaired fasting glucose, has also been associated with chronic inflammation, insulin resistance, and endothelial dysfunction [4], [5]. Habitual consumption of green tea (Camellia sinensis), a popular beverage used in traditional Chinese medicine, has been associated with decreased risks for obesity [6], diabetes [7], [8], hypertension [9], dyslipidemia [10], [11], and CVD mortality [12], [13], [14] in several epidemiological studies. In selected clinical trials, green tea supplementation has been shown to significantly improve features of metabolic syndrome, such as decreased abdominal adiposity indicated by waist circumference in obese subjects [15], [16], [17], reduced blood glucose and hemoglobin A1C in prediabetic or diabetic patients [18], [19], improved postprandial lipid responses in subjects with mild hypertriglyceridemia [20], and increased flow-mediated dilation in smokers or subjects with endothelial dysfunction [21], [22]. However, these epidemiologic and clinical studies have been mostly conducted in populations in Asian countries with habitual green tea consumption. Also, in some trials outcomes are significant versus baseline but not control group, or are possibly confounded by the habitual caffeine intake by the subjects, or caffeine content in green tea. Thus, these limited human studies showing positive effects of green tea in metabolic syndrome emphasize the need for further controlled intervention trials using decaffeinated green tea in populations with salient features of metabolic syndrome and CVD risk factors.
Clinical trials have reported mixed results on the effects of green tea on biomarkers of inflammation, which is associated with metabolic syndrome and CVD. In an uncontrolled study in male smokers, green tea consumption (600 mL/d) for 4 wk was shown to decrease P-selectin levels, suggesting a decrease in risk factors of atherosclerosis in these subjects [23]. In contrast, in a randomized controlled study, green tea intervention (900 mL green tea or 3.6 g green tea polyphenols) for 4 wk showed no effects on inflammatory markers such as C-reactive protein (CRP), interleukin-6 (IL-6), interleukin- 1β (IL-1β), or tumor necrosis factor-α in healthy smokers [24]. In a postprandial study, green tea intake (6 g) versus controls improved endothelial function, but had no effects on biomarkers of inflammation in healthy individuals [25]. Studies in subjects with borderline diabetes or diabetes have shown no significant effects of green tea consumption (456 g green tea catechins for 2 mo or 900 mL of green tea for 4 wk) on markers of inflammation [18], [26]. Thus, based on these results, anti-inflammatory effects of green tea supplementation need further investigation in subjects with metabolic syndrome in controlled long-term intervention trials.
Several mechanistic studies using animal models of obesity, metabolic syndrome, and CVD also provide data substantiating the anti-obesity [27], [28], anti-diabetic [29], [30], anti-hypertensive [31], [32], anti-hyperlipidemic [33], [34], and anti-inflammatory [35], [36] effects of green tea. Ramadan et al. [34] have reported the effects of a 28-d supplementation of green tea aqueous extracts in significantly alleviating hyperglycemia, dyslipidemia, and impaired liver function in male Wistar albino rats fed a cholesterol-rich diet. Ramesh et al. [35] have shown anti-inflammatory effects of intraperitoneal administration of EGCG (100 mg/kg body weight) in significantly reducing serum CRP levels and hematologic markers of inflammation in rats fed an atherogenic diet versus the untreated group. Oral administration of EGCG (100 mg/kg body weight) in aged male Wistar albino rats fed a high-fat diet was also shown to significantly decrease CRP and tumor necrosis factor-α versus the unsupplemented group [36]. Thus, these animal studies show the benefits of green tea extracts or EGCG treatment in reversing high-fat diet induced inflammation and glucose and lipid abnormalities associated with metabolic syndrome. These potential benefits of green tea need to be confirmed in clinical trials, especially in US populations with increasing prevalence of obesity and metabolic syndrome [37].
Thus, the objective of our study was to test whether daily consumption of green tea beverage (4 cups/d) or extracts (2 capsules/d and 4 cups water/d) over a period of 8 wk would affect biomarkers of inflammation and features of metabolic syndrome versus age- and gender-matched no treatment (4 cups water/d) group, thereby lowering CVD risk factors in the US population with metabolic syndrome.
Section snippets
Subjects
Forty-one subjects with metabolic syndrome were recruited by flyers and e-mail advertisements at the General Clinical Research Center (GCRC) at University of Oklahoma Health Sciences Center. Subjects were included in the study if they had three of five features of metabolic syndrome as defined by the National Cholesterol education Program, Adult Treatment Panel III guidelines [38]. Participants were excluded from the trial if they were under 21 y of age, had a preexisting condition (e.g.,
Results
Forty-one individuals were recruited for the study. Two people withdrew due to relocation and personal reasons, and four were withdrawn on account of starting cholesterol- (one) and glucose-lowering (one) medications during the study, and for smoking (two). Thus, a total of 35 subjects completed the study with a mean age of 42.5 ± 1.7 y and a mean body mass index of 36.1 ± 1.3 kg/m2 at the screening visit. No significant differences were noted in baseline characteristics except for total and
Discussion
To our knowledge, this is the first study investigating the effects of decaffeinated green tea supplementation on biomarkers of inflammation and features of metabolic syndrome in obese population in the US. Our study results show that green tea beverage or extract supplementation selectively lowers plasma SAA versus the no treatment group. However, green tea intervention did not affect inflammatory markers including CRP, IL-6, IL-1β, sVCAM-1, sICAM-1, adiponectin, and leptin or features of
Conclusion
Green tea beverage or extract supplementation in obese subjects with metabolic syndrome for 8 wk was well tolerated and reduced circulating SAA versus no treatment group, but did not affect other biomarkers of inflammation (CRP, IL-6, IL-1β, sICAM-1, sVCAM-1), adiponectin, and features of metabolic syndrome. Thus, green tea may be included as part of a comprehensive strategy involving diet, exercise, and specific dietary supplementations aimed at reversing inflammation, endothelial dysfunction,
Acknowledgments
This work was supported by the University of Oklahoma Health Sciences Center General Clinical Research Center Grant M01-RR14467, National Center for Research Resources, National Institutes of Health. This work was also supported by a Core Research grant from College of Human Environmental Sciences, Oklahoma State University.
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Cited by (0)
This study was presented in part at the 49th Annual meeting of the American College of Nutrition and won the Best Poster Award in 2008 (http://www.americancollegeofnutrition.org/Default.aspx?tabid=121).
Conflicts of interest: None.