Lean mass and physical activity as predictors of bone mineral density in 16-20-year old women

Objective. The aim of the study was to quantify the inter-relationship betw een bone mineral density and physical activity, muscle strength, and body m ass composition in a group of healthy 16-20-year-old women. Design. A cross-sectional study. Setting. Reykjavik area. Subjects. Two-hundred and fifty-four Icelandic Caucasian women aged 16, 18 and 20 years, randomly selected from the registry of Reykjavik. Main outcome measures. Bone mineral content (BMC) and density (BMD) in lumb ar spine, hip, distal forearm and total skeleton and lean mass and fat mass were measured with dual energy X-ray absorptiometry (DEXA) and compared wi th grip strength measured with a dynamometer and physical activity as asses sed by a questionnaire. Results, The lean mass had the strongest correlation with BMC and BMD, stro nger than weight, height and fat mass, both in univariate analysis (r = 0.4 1-0.77; P < 0.001) and in linear regression analysis. The total skeletal BM D was logarithmically higher by hours of exercise per week (P < 0.001)). Ab out 30% of variability in total skeletal BMD in this age group can be predi cted by lean mass and physical exercise. Conclusions, Modifiable factors, such as exercise and adequate muscle seem to be significant predictors of the attainment of peak bone mass in women.