Lessons learned from school-based intervention trials: UBC Healthy Bones Studies.

The aim of this summary is, first, to outline the normal pattern of bone mineral accrual during childhood. From that foundation I review some intervention trials including those conducted at the University of British Columbia that evaluate the role of childhood physical activity on bone mass and bone structure. The normal pattern of bone mineral accrual was demonstrated in a 7-year longitudinal study conducted at the University of Saskatchewan in Canada 1. We measured total BMC with DXA in approximately 200 children annually for 7 years. The findings are summarized for boys and girls in Figure 1. The velocity curves illustrate the sex difference in the timing of peak bone mineral accrual, which, for the total body, occurs about 1.4 years earlier in girls (grey line) than in boys (black line) and is of a lesser magnitude (320 ± 58 g/y for girls vs. 400 ± 96 g/y for boys). Peak height velocity (PHV, maximum rate for linear growth) preceded the age of peak bone mineral accrual (maximum rate of increase in total body bone mineral) by more than half a year 1. This is of clinical interest because the dissociation between accelerated linear growth and peak bone mineral accrual might constitute a period of relative bone fragility that could partly explain the increased fracture rate observed during adolescence 2. A number of excellent review articles 3 and chapters 4-6 and books 7 all conclude that appropriate physical activity augments bone health during childhood. Retrospective studies indicate that bone responds more favorably to mechanical loading during childhood and adolescence than it does in adulthood 8,9. A study from Finland showed that racquet-players who had started playing before menarche had a 2–4 times greater dominant-nondominant side-to-side difference than those players who started playing their sport after menarche 10. These findings launched a series of intervention trials that aimed to examine the components of exercise that were most effective for promoting bone health in childhood. The interventions all involved running and/or jumping performed for 20–40 minutes, 2–3 times per week. They increased BMC, areal BMD (aBMD), and volumetric BMD (vBMD) across several sites in premenarcheal girls 11 , aBMD and vBMD in prepubertal boys 12 , trochanteric aBMD in a combined group of girls and boys 13 , and lumbar spine and femoral neck BMC in both premenarcheal girls 14 and young prepubertal (5.9–9.8 years) girls and boys 15. In other prospective …