The means ± standard deviations (SDs) or medians (interquartile ranges [IQRs]) were used to present the baseline characteristics of the participants. Categorical variables are presented as percentiles. Group differences were assessed by analysis of variance and chi-square (χ2) tests. To eliminate individual variations in urine excretion, we adjusted the mVOCs by calculating the ratio of mVOCs to urinary creatinine.