Mitigation of oxidative damage by green tea polyphenols and Tai Chi exercise in postmenopausal women with osteopenia

Abstract

Background: Osteoporosis is a degenerative bone disease predominantly in postmenopausal women. Green tea polyphenols (GTP) and Tai Chi (TC) have been shown to be beneficial on human bone health. This study examined the efficacy of GTP and TC on mitigation of oxidative damage in postmenopausal women with osteopenia.

Methods: A 6-month randomized and placebo-controlled clinical trial was conducted in 171 postmenopausal women with osteopenia, who were recruited from Lubbock County, Texas. These participants were treated with placebo, GTP (500 mg daily), placebo + TC (60-minute group exercise, 3 times/week), or GTP (500 mg daily) + TC (60-minute group exercise, 3 times/week), respectively. Their blood and urine samples were collected at the baseline, 1-, 3- and 6-months during intervention for assessing levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidative DNA damage biomarker, and concentrations of serum and urine GTP components.

Results: The elevated concentrations of serum and urinary GTP components demonstrated a good adherence for the trial. A significant reduction of urinary 8-OHdG concentrations was found in all three treated groups during 3-month (P<0.001) and 6-month (P<0.001) intervention, as compared to the placebo group. The significant time- and dose-effects on mitigation of the oxidative damage biomarker were also found for GTP, TC, and GTP+TC intervened groups.

Conclusion: Our study demonstrated that GTP and TC interventions were effective strategies of reducing the levels of oxidative stress, a putative mechanism for osteoporosis in postmenopausal women, and more importantly, working in an additive manner, which holds the potential as alternative tools to improve bone health in this population.

Trial registration: ClinicalTrials.gov NCT00625391.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Flow chart of the trial.

Figure 2. Mean (±SEM) serum GTP concentrations in study participants in the clinical trial.

A: serum EGCG concentrations; B: serum ECG concentrations. Starting from first month, serum EGCG and ECG kept constant with minor fluctuations in the GTP and GTP+TC groups. The differences among different time points (1-, 3-, or 6-months) within each group and between groups were tested with repeated measures ANOVA followed by Bonferroni correction for multiple comparisons for each outcome and the significant difference was found in EGCG concentrations in the GTP group between 3- and 6-months (P<0.050). No significant differences were found between these two groups at each time point (P>0.050).

Figure 3. Mean (±SEM) urinary GTP concentrations in study participants in intervention groups.

A: urinary EC concentrations; B: urinary EGC concentrations. Starting from first month, urinary EC and EGC concentrations kept constant with minor fluctuations in GTP and GTP+TC groups. No significant differences were found between these two groups at same time points (P>0.050, tested with Wilcoxon rank sum test). The differences among differnt time points within each group were tested with Friedman’s test followed by Wilcoxon signed rank test with Bonferroni correction for multiple comparisons for each outcome and the significant difference only existed in the EGC concentrations in GTP+TC group between 1- and 3-months (P<0.050).

Figure 4. Urinary 8-OHdG concentrations in study participants in different groups.

A: baseline, no significant differences in urinary 8-OHdG were found (P = 0.299); B: 1 month, urinary 8-OHdG concentrations were reduced by all treatments, but no significant differences were observed (P = 0.110); C: 3 month, urinary 8-OHdG concentrations were significantly reduced in all treatment groups (P<0.001); D: 6 month, urinary 8-OHdG concentrations were significantly reduced in all treatment groups (P<0.001).

Figure 5. Temporal patterns of urinary 8-OHdG concentrations in study participants.

A: Placebo, no significant differences was observed in different treatment periods (P = 0.133); B: TC, compared to baseline, urinary 8-OHdG concentrations were significantly reduced at 1-, 3-, and 6- months treatment (P<0.001); C: GTP, compared to baseline, urinary 8-OHdG concentrations were all significantly reduced at 1-, 3-, and 6-months treatment (P<0.001); and D: GTP+TC, compared to baseline, urinary 8-OHdG concentrations were all significantly reduced at 1-, 3- and 6-months treatment (P<0.001).