Adolescent obesity rates remain at an all-time high. Obesity and osteoporosis are interrelated diseases, yet little is known about how changes in soft tissue composition affect bone development during adolescence, a critical time for bone mineral accrual. The aim of this study was to assess the contributions of changes in lean and fat mass on changes in bone strength in adolescent females.
Bone strength strain index (SSI) was assessed at the 20% distal femur, 66% distal tibia, and 66% distal radius of the non-dominant limb using peripheral quantitative computed tomography (pQCT). Total body lean and fat masses were measured by dual-energy x-ray absorptiometry (DXA). All measurements were taken at baseline and 2-year follow-up. Multivariable linear regression was used to assess the independent effects of changes in fat and lean mass (kg) on SSI change, adjusting for baseline SSI, maturity offset, and ethnicity; fully adjusted models included mutual adjustment for fat and lean.
Hispanic (n=111) and non-Hispanic (n=46) girls, mean age 10.9 ± 1.1 and BMI 20.9 ± 5.2 at baseline, participated. Change in fat mass was a significant (p ≤ 0.001) predictor of change in tibia (β: 11.14, 95% CI: 6.15, 16.12), femur (β: 15.09, 95% CI: 7.21, 22.97), and radius (β: 1.37, 95% CI: 0.45, 2.29) SSI. Similarly, change in lean mass was a significant (p < 0.001) predictor of change in tibia (β: 22.17, 95% CI: 16.03, 28.31), femur (β: 34.56, 95% CI: 25.58, 43.55), and radius (β: 3.40, 95% CI: 2.24, 4.55) SSI. In mutually adjusted models, change in fat mass did not significantly predict change in SSI at any bone sites, while change in lean mass remained a significant predictor of SSI change (p < 0.001) at all bone sites.
Change in lean mass, but not fat, is the primary predictor of SSI change at the tibia, femur, and radius in adolescent females during the 2 years surrounding peak bone mineral accrual.