The data were analyzed using SigmaPlot software (version 12.0, Systat, San Jose, California, USA). The normal distribution of variables was evaluated using the Shapiro-Wilk test. The differences in demographic and hematological measurement data between the MS and non-MS groups were analyzed using Student's t-test or the Mann-Whitney rank sum test. For categorical response variables, differences between the two groups were assessed using the Chi-square test or Fisher's exact test. Adjusted odds ratios with 95% confidence intervals (CI) for MS were calculated from the logistic regression models base on the fifth level (50th percentile) of antioxidant enzymes activities. The data are expressed as the means ± the standard deviations (SD). The results were considered statistically significant at P < 0.05.