摘要Objective This study aimed to investigate possible serum 25-hydroxyvitamin D[25(OH)D]cutoffs for the associations between 25(OH)D and Bone turnover markers(BTMs),and how GC gene variation influences such cutoffs in Chinese women of childbearing age.Methods In total,1,505 non-pregnant or non-lactating women(18-45 years)were recruited from the 2015 Chinese Adult Chronic Disease and Nutrition Surveillance.Serum 25(OH)D,osteocalcin(OC),procollagen type 1 N-terminal propeptide(P1NP),β-CrossLaps of type 1 collagen containing cross-linked C-telopeptide(β-CTX),and single nucleotide polymorphisms were determined.Locally weighted regression and smoothing scatterplot and segmented regression were performed to estimate the 25(OH)D thresholds.Results The median serum 25(OH)D was 16.63(11.96-22.55)ng/mL and the prevalence of low serum 25(OH)D(<12 ng/mL)was 25.2%.Women with the lowest 25(OH)D had the highest β-CTX.After adjustment for the confounders,25(OH)D cutoffs for OC[14.04(12.84-15.23)ng/mL],β-CTX[13.94(12.49-15.39)ng/mL],and P1NP[13.87(12.37-15.37)ng/mL]in the whole population,cutoffs for OC[12.30(10.68-13.91)ng/mL],β-CTX[12.23(10.22-14.23)ng/mL],and P1NP[11.85(10.40-13.31)ng/mL]in women with the GC rs2282679 G allele,and cutoffs for OC[12.75(11.81-13.68)ng/mL],β-CTX[13.05(11.78-14.32)ng/mL],and P1NP[12.81(11.57-14.06)ng/mL]in women with the GC rs2282679 T allele,were observed.Below these cutoffs,BTMs were negatively associated with 25(OH)D,while above these cutoffs,BTMs plateaued.Conclusion In Chinese women of childbearing age,there were thresholds effect of serum 25(OH)D concentrations on BTMs.The results indicated that serum 25(OH)D concentrations<13.87 ng/mL in this population had adverse influences on maintaining bone remodeling.BTMs were suppressed at a relatively lower serum 25(OH)D in women with the GC rs2282679 G allele compared with those with the T allele.