Physical activity is associated with increased volumetric bone density and bone strength in early childhood

Abstract

Introduction: Both femoral geometry and bone mass have been shown to independently to predict both hip strength and fracture risk in adults. Whereas intrauterine and early postnatal life has been shown to influence bone mass, the relationship between hip geometry and strength is poorly understood. We therefore used a large prospective cohort study to explore the relationships between growth and lifestyle in early life and hip geometry, strength and volumetric density at 6 years old. Methods: Children were recruited at 6 years old from the Southampton Women's Survey. Their mothers diet lifestyle and anthropometry had previously been characterised before and during pregnancy. The children underwent measurement of bone mass by DXA (Hologic), including hip structure analysis (HSA), and by pQCT at the tibia (Stratec). Physical activity (PA) was assessed by accelerometry (Actiheart, Cambridge Neurotechnology Ltd, Cambridge, UK) for 7 continuous days. Diet was assessed using a validated food frequency questionnaire and detailed anthropometric data was also collected. Results: There were 215 children with PA data who underwent a DXA scan, of these 49 children also underwent pQCT assessment. Mean daily time spent in vigorous activity (VPA) was positively associated increased measures of volumetric BMD for whole body (r=0.32, p<0.001), lumbar spine (r=0.16, p=0.02) and hip (r=0.15, p=0.03). In the subset that underwent pQCT, VPA was positively related to cortical volumetric bone mineral density (r=0.29, p=0.05). Increased daily time in VPA was also positively associated with femoral neck and intertrochanteric section modulus (r=0.23, p=0.001; r=0.23, p=0.001 respectively), cross sectional area (CSA) (r=0.26, p=0.0002; r=0.24, p=0.0009) and cortical thickness (r=0.17, p=0.02; r=0.19, p=0.009). These relationships were independent of maternal and childhood dietary, lifestyle and anthropometric factors. Similar associations for VPA with section modulus (r=0.17, p=0.02) and CSA (r=0.16, p=0.02) were observed at the femoral shaft. Conclusions: Higher levels of vigorous physical activity in childhood are associated with increased femoral neck strength, both in terms of geometric shape and volumetric mineral density. This work supports the notion that increasing physical activity in childhood is likely to be a potential public health strategy to improve childhood skeletal development and reduce the burden of osteoporotic fracture in later life.