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 between bone mineral density and physical activity, muscle strength, and body mass 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 lumbar spine, hip, distal forearm and total skeleton and lean mass and fat mass were measured with dual energy X-ray absorptiometry (DEXA) and compared with grip strength measured with a dynamometer and physical activity as assessed by a questionnaire. Results. The lean mass had the strongest correlation with BMC and BMD, stronger than weight, height and fat mass, both in univariate analysis (r= 0.41-0.77; P < 0.001) and in linear regression analysis. The total skeletal BMD was logarithmically higher by hours of exercise per week (P < 0.001)). About 30% of variability in total skeletal BMD in this age group can be predicted 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.