Background:Obstructive sleep apnea syndrome (OSAS) is prevalent in obesity and is associated with many metabolic abnormalities.The relationship between OSAS and bone metabolism is still unclear.The aim of this study was to investigate the relationship between the severity of OSAS and bone metabolic markers.Methods:A total of 119 obese males were enrolled in this study in spring months from 2015 to 2017.All candidates underwent polysomnography,and their bone mineral density (BMD) and the serum levels of total procollagen type 1 N-terminal propeptide (t-P 1NP),N-terminal midfragment of osteocalcin (N-MID),β-C-terminal telopeptide of type 1 collagen (β-CTX),vitamin D (VD),and parathyroid hormone (PTH) were measured.The analysis of variance and Pearson correlation analysis were performed for data analyses.Results:No significant differences in the mean values of BMD were observed among the obesity,mild-to-moderate OSAS,and severe OSAS groups;and the serum levels oft-P1NP and β-CTX in the severe OSAS group were significantly higher than those in the obesity group (48.42 ± 23.78 ng/ml vs.31.98 ± 9.85 ng/ml,P ＜ 0.001;0.53 ± 0.24 ng/ml vs.0.41 ± 0.13 ng/ml,P =0.011,respectively).The serum level of VD in the obesity group was significantly higher than those in the mild-to-moderate and severe OSAS groups (both P ＜ 0.001),and decreased as the severity of OSAS increased (P ＜ 0.001).The serum level of PTH in the severe OSAS group was significantly higher than those in the obesity and mild-to-moderate OSAS groups (both P ＜ 0.001).The results of correlation analysis indicated that the level of apnea-hypopnea index (AHI) was correlated with the levels of t-P1NP (r =0.396,P ＜ 0.001),VD (r =-0.404,P ＜ 0.001),and PTH (r =0.400,P ＜ 0.001),whereas the level of minimum O2 saturation (SaO2min) was correlated with the levels ofVD (r =0.258,P =0.016) and PTH (r =-0.376,P ＜ 0.001).Conclusions:The levels of bone resorption and formation markers in patients with severe OSAS were significantly increased compared to obese men,and the severity of OSAS was correlated with the serum levels oft-P1NP,VD,and PTH.