Abstract
ABSTRACTLater 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 age 2 years and bone outcomes obtained by dual‐energy X‐ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) scans at ages 60 to 64 years in a nationally representative cohort study of British people, the MRC National Survey of Health and Development. It was hypothesized 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 (standardized regression coefficients with 95% confidence interval [CI] –0.179 [–0.251 to –0.107]), spine (–0.157 [–0.232 to –0.082]), and distal radius (–0.159 [–0.245 to –0.073]) bone mineral content (BMC, indicating bone compressive strength) in men (all p < 0.001). Adjustment for covariates partially attenuated these associations, primarily because of 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. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.
Highlights
The large muscle and impact forces associated with locomotion have a pronounced effect on lower limb bone strength; athletes engaged in sprinting and running have up to 23% higher bone mineral content (BMC, an indicator of bone compressive strength) than sedentary controls,(1) whereas cessation of ambulation in spinal cord injury patients leads to a loss of 30% of lower limb BMC.[2]. Onset of independent walking at around 12 to 18 months of age represents the first postnatal exposure of the lower limbs to these forces
Previous studies have identified strong associations between later attainment of independent walking and other locomotor activities, and lower tibial BMC and cross-sectional moment of inertia (CSMI, an indicator of bone bending/torsional strength) in young children,(3) and tibia/hip BMC and tibia CSMI in adolescents.[4]. These associations were partly mediated by lower lean mass in later walkers, which may be acting as a marker of lower physical activity
Unadjusted regression models showed that later walking age was associated with lower total hip BMC in men (Fig. 1A, model 1); similar associations were observed for total hip bone mineral density (BMD) and bone area (BA) (Supplemental Table S2)
Summary
The large muscle and impact forces associated with locomotion have a pronounced effect on lower limb bone strength; athletes engaged in sprinting and running have up to 23% higher bone mineral content (BMC, an indicator of bone compressive strength) than sedentary controls,(1) whereas cessation of ambulation in spinal cord injury patients leads to a loss of 30% of lower limb BMC.[2]. Given that development of independent walking can be modified in both healthy children[6] and in groups prone to delayed motor development,(7,8) this may offer an opportunity for improving lifelong bone health. It is unknown whether associations between age at walking onset and bone strength persist into older age. Hip fractures are rare in children and adolescents[9] but represent the most common fracture site in older individuals.[10] Given that hip bone strength is an important risk factor for future fracture,(10) it is relevant to establish the long-term potential consequences of later development of walking on bone health in later adulthood. Previous studies investigating associations between walking age and bone have only investigated lower limb bone strength, and associations between early life movement and central or upper limb sites such as the spine or distal radius (where fractures are common and/or lead to a substantial burden on health services) are unknown
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