Later age at onset of independent walking is associated with lower leg bone strength in childhood and adolescence. However it is unknown whether these associations persist into older age, or whether they are evident at axial (central) or upper limb sites. Therefore we examined walking age obtained at 2y and bone outcomes obtained by dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) scans at 60-64y in a nationally-representative cohort study of British people, the MRC National Survey of Health and Development. It was hypothesised that later walking age would be associated with lower bone strength at all sites.
Later independent walking age was associated with lower height-adjusted hip (standardised regression coefficients with 95%CI) [-0.179(-0.251,-0.107)], spine [-0.157(-0.232,-0.082)] and distal radius [-0.159(-0.245,-0.073)] bone mineral content (BMC, indicating bone compressive strength) in men (all P < 0.001). Adjustment for covariates partially attenuated these associations, primarily due to lower lean mass and adolescent sporting ability in later walkers. These associations were also evident for a number of hip geometric parameters (including cross-sectional moment of inertia (CSMI), indicating bone bending/torsional strength) assessed by Hip Structural Analysis (HSA) from DXA scans. Similar height-adjusted associations were also observed in women for several hip, spine and upper limb outcomes, although adjustment for fat or lean mass led to complete attenuation for most outcomes, with the exception of femoral shaft CSMI and spine bone area (BA).
In conclusion, later independent walking age appears to have a lifelong association with bone strength across multiple skeletal sites in men. These effects may result from direct effects of early life loading on bone growth, and mediation by adult body composition. Results suggest that late walking age may represent a novel risk factor for subsequent low bone strength. Existing interventions effective in hastening walking age may have positive effects on bone across life.