Association Of Daily Steps With Bone Mineral Density And Bone Metabolism Indicators In Preschool Children: A Longitudinal Study

Purpose: Preschool is a critical period for the growth and development of the human skeletal system,and obtaining high Peak Bone Mass(PBM)during preschool can reduce the risk of osteoporosis and fracture in adulthood.Previous studies in adolescents and adults have found an association between daily steps and BMD and bone metabolism indicators.However,there are fewer studies on daily steps and BMD in preschool children.The aim of this study was to investigate the relationship between daily steps and BMD and bone metabolism indicators in preschool children.Methods: Children aged 3-6 years in 2 rural kindergartens in a rural area of Gansu Province were studied at baseline in September 2021 and followed up in April 2022.Xiaomi smart sports bracelets were used to detect the daily step counts of preschool children.Bone mineral density(BMD),bone mineral content(BMC),bone mineral area(AREA),and bone mineral density(BMD)were measured by Dual-Energy X-Ray Absorptiometry(DXA)in the non-dominant forearm and heel bones of preschool children.(AREA),BMD Z-score(Z-BMD)and BMD Z-score percentile(Z-Ratio)].Fasting blood was collected from the children,and bone metabolism indicators [β-Collagen degradation products(β-CTX),Tartrate-Resistant Acid Phosphatase 5b(TRAP 5b),Osteocalcin(OC),bone-specific alkaline phosphatase(BSP)Bone-Specific Alkaline Phosphatase(B-ALP),25-Hydroxyvitamin D(25(OH)D),25(OH)D2,25(OH)D3,Parathyroid Hormone(PTH))and Insulin-Like Growth Factor 1(IGF-1)]concentrations.A multiple linear regression model was used to investigate the relationship between daily and weekly step counts and BMD and bone metabolism indicators in preschool children,and a segmented regression model was used to analyze the threshold effects of daily step counts on BMD and bone metabolism indicators in preschool children.Results: A total of 416 preschool children,204 boys and 212 girls,with a mean age of4.54(0.60)years,were included in this study.(1)In the fully corrected model,the baseline daily step count was correlated with the nondominant lateral forearm[regression coefficient β values and 95% CI values were: 0.001(0.000-0.003)and 0.003(0.001-0.005),respectively] and heel [regression coefficient β values and 95% CI values were: 0.002(0.000-0.003)and 0.002(0.000-0.003)] were positively correlated with both BMD and BMC,as well as with the bone metabolic indicators 25(OH)D concentration [regression coefficient β value and 95% CI: 0.243(0.039-0.446)].(2)At follow-up compared with baseline,in the fully corrected model,the change in the number of steps per day in preschool children was positively correlated with the change in BMD and BMC in the non-dominant heel bone [regression coefficient β and 95% CI values were: 0.001(0.000-0.002)and 0.001(0.000-0.002),respectively],while there was no correlation with the change in the bone metabolism indicators.relationship.(3)As can be observed from the smoothed curve fit plots,in the fully corrected model,baseline daily steps were positively correlated with both BMD and BMC in the nondominant forearm and heel;the results of the threshold effect analysis showed that the differences in regression coefficients before and after the fold points of BMD and BMC in the nondominant forearm and heel at baseline daily steps were not statistically different from each other,and were only statistically different from the BMD likelihood ratio test in the nondominant forearm differences.(4)From the results of the smoothed curve fit plots and threshold effect analysis,it was observed that in the fully corrected model,baseline daily step was nonlinearly correlated with B-ALP,25(OH)D2,and PTH concentrations,whereas it was positively correlated with 25(OH)D3 concentration;the fold points of baseline daily step with B-ALP,25(OH)D2,25(OH)D3,and PTH concentrations were 5.334,6.402,5.642 and 11.302 kst/day,respectively,and the difference in regression coefficients and likelihood ratio tests before and after the fold point were statistically different.(5)In the fully corrected model,the baseline weekly step attainment days of preschoolers were correlated with the non-dominant forearm[regression coefficient β values and 95% CIs of 0.002(0.000-0.004)and 0.003(0.001-0.006),respectively] and heel [regression coefficient β values and 95% CIs of 0.002(0.000-0.004)and 0.002(0.000-0.004)] were positively correlated with both BMD and BMC,as well as with 25(OH)D concentration [regression coefficient β value and 95%CI: 0.319(0.032-0.607)].(6)At follow-up compared with baseline,in the fully corrected model,the value of the change in the number of days per week step attainment in preschool children was positively correlated with the value of the change in BMD and BMC in the non-dominant side of the heel only [regression coefficient β values and 95% CI values were: 0.001(0.000-0.002)and 0.001(0.000-0.002),in that order],while with the non-dominant side of the forearm There was no correlation with the change values of BMD,BMC and bone metabolic indicators in the non-dominant forearm.Conclusion:(1)the daily step count and the number of days to reach the weekly step count in preschool children were positively correlated with the BMD and BMC of the nondominant side of the heel bone,i.e.,the more the daily step count and the number of days to reach the weekly step count,the higher the BMD and BMC of the nondominant side of the heel bone;(2)no significant threshold effects were found between the daily step count and the BMD and BMC of the nondominant side of the forearm and heel bone in preschool children;(3)no(3)no significant threshold effects were found between daily steps and different bone metabolic indicators in preschool children.