SAT-527 Femoral Neck Strength and Vitamin D in Older African American Women

Abstract

Purpose: Bone Mineral density (BMD) is a predictor of fracture risk. Beyond BMD, the role of vitamin D for bone strength is not known in African American (AA) population. Objective: To examine the effect of vitamin D supplementation on femoral neck (FN) strength. Design and Setting: A 3-year randomized, double-blind, placebo-controlled clinical trial. Participants: 260 healthy postmenopausal AA women aged 65 years and older. Main Outcome Measures: Femoral axis length and width were measured by dual-energy x-ray absorptiometry. We combined these variables with BMD, body weight and height and computed composite indices of FN strength: compression strength index (CSI), bending strength index (BSI), and impact strength index (ISI). Results: Mean age of participants was 68.2 ± 4.9 years. Baseline characteristics between groups were similar. The average dose of vitamin D3 was 3490 ± 1465 IU/day. Serum 25(OH)D concentration was maintained at above 30 ng/mL in the active group. The average serum 25(OH)D at the 3-year period was 46.8 ± 1.2 ng/mL in the active group compared to 20.7 ± 1.1 ng/mL in the placebo group. Linear mixed effects models demonstrated a significant linear increase in FN width, BSI and ISI over time in both active and placebo group (all p values <0.05). However, there was no group × time interaction effect for any composite indices suggesting that the longitudinal differences in CSI, BSI and ISI between groups were not statistically significant (all p values >0.05). Conclusion: These findings indicate no treatment effect of vitamin D on bone strength in African Americans. Maintaining serum 25(OH)D above 30 ng/ml did not affect bone strength. There is no evidence to support vitamin D intake greater than the recommended RDA by the Institute of Medicine in this population for bone health.