Relationship between Body Composition and Physical Activity with Bone Mineral Density in Postmenopausal Women 40-60

Osteoporosis is a debilitating disease diagnosed by either a fragile fracture or bone mineral density test (DXA). DXAs are typically not ordered or covered by insurance until women are over 65. There is a need for noninvasive, easily administered, readily available screening tools that can predict low bone mineral density before significant losses occur. PURPOSE: To determine the relationship between objectively measured physical activity (accelerometry), lower extremity strength (sit to stand test) and body composition with bone mineral density in otherwise healthy, community dwelling women. METHODS: A secondary, exploratory analysis of baseline data from post-menopausal women (n=150) collected as part of a larger RCT of 290 women. Bone mineral density (BMD): femoral neck (FN), total femur (TF), and lumbar spine (LS) (L1-L4) and body composition: total fat mass (FM), total lean mass (LM), and lower extremity lean mass (LELM) were measured by DXA (GE model iDXA; software 14.10.002). Lower extremity strength was measured with timed stand test. Physical activity (PA) was measured by accelerometers (Actigraph GT3+) worn on the non-dominant wrist for 4 days (n=103/155) and analyzed using Actilife software (v 6.12, 60 second epochs) to determine minutes of activity of varying intensities. RESULTS: No statistically significant relationships between PA (sedentary, light or moderate activity) and BMD at the FN, TF or LS (p>0.05). BMI, LM and FM were significantly related to FN (r 2 =0.28, r 2 =0.29, r 2 =0.28) and TF (r 2 =0.36, r 2 =0.27, r 2 =0.34) (p<0.001). LELM had a significant relationship with FN BMD (r 2 =0.24, p<0.001). When adjusted for BMI, FM was no longer statistically significant at FN and TF (p>0.05) while both LELM and total lean mass remained significant at the FN (p<0.001). No statistically significant relationship was found between sit to stand time and BMD (p>0.05). CONCLUSION: In middle aged women, BMI, FM and LM are related to FN & total femur BMD. When controlled for BMI, only LM remained predictive of BMD supporting the potential for an easy, noninvasive measurement of lower extremity strength. However, neither PA (wrist worn accelerometer) nor the sit to stand test were significantly related to BMD. Supported by NIH/NINR Grant: R01NR013913,Ryan