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Physical activity and bone measures in young children: the Iowa bone development study
K F Janz1, T L Burns, J C Torner
1Department of Health, Leisure, and Sport Studies, University of Iowa, Iowa City, IA 52242, USA. kathleen-janz@uiowa.edu.
Insights
Physical activity in preschool children is linked to better bone health. Promoting activity in early childhood may support optimal bone development before peak bone mass is reached.
Area of Science:
- Pediatric bone health
- Childhood physical activity
- Growth and development
Background:
- Physical activity benefits bone development in older children.
- The impact of physical activity on bone health in younger children remains less understood.
- Early childhood is a critical period for establishing foundational bone mass.
Purpose of the Study:
- To investigate the association between physical activity and bone measures in preschool children.
- To determine if different measures of physical activity correlate with bone mineral content and density.
- To explore the relationship between sedentary behavior (television viewing) and bone health in this age group.
Main Methods:
- Cross-sectional study of 368 preschool children (ages 4-6).
- Physical activity assessed via accelerometry and parental reports.
- Bone mineral content and bone mineral density (BMD) measured using dual-energy X-ray absorptiometry.
Main Results:
- Physical activity, measured by accelerometry and parental report, showed consistent positive associations with bone mineral content and BMD in both boys and girls.
- Higher levels of vigorous physical activity and overall reported activity were significant predictors of better bone measures.
- Television viewing was inversely associated with hip bone mineral density in girls.
Conclusions:
- Significant associations exist between physical activity and bone measures in early childhood.
- These findings suggest that interventions promoting physical activity in young children can positively impact bone development.
- Early physical activity may contribute to achieving optimal peak bone mass later in life.
Objectives:
Physical activity has a beneficial effect on bone development in circumpubertal children, although its effect on younger children is uncertain. In this cross-sectional study, we examined associations between physical activity and bone measures in 368 preschool children (mean age: 5.2 years, range: 4-6 years).
Design:
Physical activity was measured using 4-day accelerometry readings, parental report of children's usual physical activity, and parental report of children's hours of daily television viewing. Total body and site-specific bone mineral content and area bone mineral density (BMD) were measured by dual energy radiograph absorptiometry.
Results:
After adjustment for age and body size, accelerometry measures of physical activity and parental report of usual physical activity were consistently and positively associated with bone mineral content and BMD in both boys and girls (r = 0.15-0.28). Television viewing was inversely associated with hip BMD in girls (r = -0.15). The proportion of variance in bone measures explained by physical activity in linear regression models ranged from r(2) = 1.5% to 9.0%. In all of these models except total body BMD, at least 1 and often several of the physical activity variables entered as independent predictors. Activity variables most likely to enter the regression models were vigorous physical activity (as determined by accelerometry) and parental ranking of child's usual physical activity.
Conclusions:
Findings indicate that there are statistically significant and, perhaps important, associations between physical activity and bone measures during early childhood, well ahead of the onset of peak bone mass. This would suggest that intervention strategies to increase physical activity in young children could contribute to optimal bone development.