Sustained Effects of Physical Activity on Bone Health: Iowa Bone Development Study
Category: Bone Acquisition and Pediatric Bone Disease
Oral Presentations, Presentation Number: 1071
Session: Concurrent Oral Session 12: Bone Acquisition and Pediatric Bone Disease
Saturday, October 13, 2012 3:15 PM - 3:30 PM, Minneapolis Convention Center, Room 200DE
* Shelby Francis, University of Iowa, USA, Elena Letuchy, University of Iowa, USA, Steven Levy, University of Iowa, USA, Kathleen Janz, University of Iowa, USA
Purpose: Previous studies of young athletes and children engaged in targeted interventions have shown some maintenance of bone mineral content (BMC; g) years after cessation of training, but less is known about the sustained effects in the average child population. Using a prospective cohort, this study examined the potential effect of early childhood physical activity (PA) on BMC in adolescence.
Methods: Participants (N=156 boys, 170 girls) in the Iowa Bone Development Study had clinical exams at ages 5, 8, 11, 13, and 15 yr. Body size and somatic maturity were measured using anthropometry. Moderate to vigorous physical activity (MVPA) and vigorous PA were measured using the Actigraph accelerometer. Due to the higher fitness level in children and adolescents compared to adults, cut points were set at ≥ 4 METs for MVPA and ≥ 7 METs for vigorous PA. BMC of the lumbar spine and hip was measured using dual-energy x-ray absorptiometry. Mixed regression models were used to test whether activity level at age 5 had an effect on BMC at ages 13 and 15 after adjustment for age 13 and 15 age (yr), height (cm), weight (kg), maturity (0=pre-peak height velocity/1=post), and activity level (min•day-1). The analysis was repeated to control for BMC at age 5.
Results: On average, boys participated in 59 min, 52 min, and 38 min of MVPA at ages 5, 13, and 15, respectively. They participated in 13 min, 17 min, and 11 min of vigorous PA at ages 5, 13, and 15, respectively. MVPA and vigorous PA at age 5 predicted spine BMC at ages 13 and 15 (p < 0.05). MVPA at age 5 predicted hip BMC. Girls participated in 47 min, 33 min, and 26 min of MVPA at ages 5, 13, and 15, respectively. They participated in 10 min, 9 min, and 7 min of vigorous PA at ages 5, 13, and 15, respectively. Neither MVPA nor vigorous PA predicted spine BMC at ages 13 and 15. MVPA at age 5 did predict hip BMC. When the analysis was repeated to control for BMC at age 5 as well as the other covariates, the effect of MVPA and vigorous PA at age 5 remained significant for boys at the spine. For girls, neither MVPA nor vigorous PA at age 5 predicted spine or hip BMC.
Conclusions: Everyday childhood activity provides bone benefits that can be sustained into adolescence. These results, especially in boys, suggest that bone strengthening physical activity programming should begin early in childhood.
* Presenting Authors(s): Shelby Francis, University of Iowa, USA