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Racial/Ethnic Differences in Bone Health, Bone Free Lean Mass, and Fat Mass in Young Women

METHODS: Young, primarily Hispanic female subjects (N=320), age 9-12 yr., wore accelerometers for seven consecutive days. Wear time was classified into sedentary, light, moderate, and vigorous activity based on Evenson cut points. Femoral and tibial bone density, content, strength, and architecture were assessed using peripheral quantitative computed tomography (pQCT). Whole body soft tissue composition was measured by DXA. Associations between each bone variable and average daily MVPA were determined using multivariate regression, adjusting for maturity offset, BMI, and ethnicity. RESULTS: Average height, weight, and percent fat were 145.8± 9.6 cm, 44.1± 14.7 kg, and 32.5± 9.8%, respectively. Multiple linear regression resulted in consistently significant (p<0.05) or trends toward significant associations between bone parameters and daily MVPA. Average daily MVPA was 22.3± 63.1 minutes. Femur 20% periosteal circumference, strength-strain index (SSI), 4% tibia average bone strength index, average periosteal circumference, average cortical thickness, and 66% tibia cortical content, periosteal circumference, and SSI all had significant associations with average daily minutes of MVPA, while other pQCT measures approached significance. The variance explained by MVPA ranged from approximately 0% to 4.8%. Together, BMI, maturity offset, and ethnicity explained 2.6% to 70.2% of the variance in the models. CONCLUSION: There is a significant positive relationship between average daily MVPA levels and bone content and strength in Hispanic girls. Physical activity interventions could lead to enhanced bone development and strength, as shown in non-Hispanic populations. Sponsored by: NIH Grant 5R01HD074565-05