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Lean mass and physical activity as predictors of bone mineral density in 16-20-year old women
O Valdimarsson1, J O Kristinsson, S O Stefansson
1Department of Internal Medicine, Reykjavik Hospital, University of Iceland, Reykjavik, Iceland.
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.