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Determinants of bone mineral density in pre-and early-pubertal asian-and causcasian-Canadians : exercise intervention and family studies

University of British Columbia

Background: There is increasing evidence that the pre- and early-pubertal years may be a biologically optimal time for exercise to influence bone mass. The primary focus of this thesis was to examine the effects of a school-based exercise intervention in pre- and early- pubescent children (study 3). A secondary objective was to examine sex and ethnic differences in BMD (study 1), and familial resemblance of total body bone, lean and fat mass (study 2). Methods & Results: 1) Sex and ethnic differences in BMD, physical activity and calcium intake were examined in 168 Asian (n=58) and Caucasian (n=110) boys (n=86) and girls (n=82). Physical activity, calcium intake, and femoral neck BMD were lower in Asian as compared to Caucasian boys (p<0.05). Caucasian girls had lower physical activity, calcium intake and BMD values at the proximal femur and its regions compared with Caucasian boys. 2) Familial resemblance was examined in 77 parents and their children. Significant correlations were observed between mothers and daughters for height, weight, lean and fat tissue, and total body bone mass (all ~r=0.50, p< 0.05). Resemblance for bone mass was also apparent for mother-son (r = 0.439, p<0.05) and father-son pairs (r=0.584, p<0.05). However, when adjusted for lean mass and height within each sex, ethnic and generation group, these correlations were no longer significant in any group. 3) Exercise intervention: A total of 144 grade 3 and 4 children from 10 Elementary schools in Richmond B.C. were randomly assigned to exercise (n=63) or control (n=81) groups. Schools in the exercise group incorporated 10-20 minutes of moderate impact activities into their physical education classes. The exercise group showed significantly greater change in femoral trochanteric BMD (4.4 vs. 3.2%, p<0.05). There were no group differences at other sites either before or after controlling for potential confounding variables. Conclusions: Results of these studies support the emerging notion that the immature skeleton is responsive to even moderate weight-bearing interventions and that other influences, including sex and ethnicity, are apparent in childhood. A school-based loading program incorporated into existing physical education curriculum is a practical way to influence bone mineral accretion during pre- and early-puberty. Longer-term intervention studies are needed to determine if benefits are maintained.

Thesis/Dissertation

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2009-07-27

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http://hdl.handle.net/2429/11342

Human Kinetics

University of British Columbia

UBCV

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