Determinants Of Bone Mineral Density In Premenopausal Women

Abstract

Listen

Translate article

In premenopausal women, osteoporosis may be diagnosed by low bone mineral density (BMD) in conjunction with secondary causes of bone loss or with risk factors for fracture. Therefore, it is important to identify determinants of low bone mass and/or risk for bone loss in this age group of women. PURPOSE The purpose of this study was to examine the influence of body composition, calcium intake, physical activity and menstrual characteristics on BMD in women, 18–30 years of age. METHODS All subjects (n=65) completed questionnaires to assess physical activity levels (Baecke), menstrual status, and calcium intakes. 36 of the women recruited for the study were taking oral contraceptives (OC). BMD and bone mineral content (BMC) at the AP lumbar spine, left proximal femur, and total body sites was measured by a pencil beam DXA. In this laboratory, in vivo precision for the spine and total body is 1.0% and ranges from 0.7% to 1.3% for the proximal femur regions of interest. Body composition variables were analyzed from the total body scans. RESULTS There were no significant differences in BMD or B between women taking OC and those not taking OC. Significant (p<.05) moderate correlations were found between BMD variables and bone-free lean body mass (r=.41−.55), whereas low correlations existed between physical activity scores and BMD (r=.27−.29). Stepwise multiple regression analyses determined that bone-free lean body mass was a significant (p<.05) predictor for each BMD site, accounting for 19.1% (spine) to 32.3% (total hip) of the variance. Fat mass and the Baecke work index score were also significant predictors of total body BMD. None of the other independent variables (calcium intake, OC use, sport index, leisure index) used in the regression analyses were significant predictors for the BMD variables. CONCLUSION Lean body mass had the strongest influence on BMD at the lumbar spine, proximal femur and total body sites. Generally, OC use, calcium intake, and physical activity scores were not significant determinants of BMD in these young women.