Date

October 2011

Document Type

Thesis

Degree Name

M.P.H.

Department

Dept. of Public Health and Preventive Medicine

Institution

Oregon Health & Science University

Abstract

Vitamin D deficiency has been previously shown to be associated with increased incidence of hip fracture. Higher serum 25(OH)D levels are also associated with greater femoral neck BMD estimated with DXA. However, there is limited current evidence supporting associations between femoral neck or shaft bone density distributions in cortical and trabecular compartments or bone size and endogenous serum 25(OH)D levels. We evaluated variation in femoral neck and shaft volumetric BMD (vBMD) and size with serum 25(OH)D in men ages ≥ 65 years from the Osteoporotic Fractures in Men Study (MrOS). Baseline fasting serum 25(OH)D levels were measured by LC/MS assays in a randomly selected sample. Femoral neck measures from quantitative computed tomography (QCT) were integral, cortical and trabecular vBMD; crosssectional area; and integral, cortical, and percent cortical volume. Femoral shaft measures included cross-sectional area, cortical area, medullary area, integral BMD and percent cortical area. The analytic cohort consisted of 888 men with serum 25(OH)D and femoral neck measures. Multivariable linear regression models with adjustments for age, race, BMI, height, latitude of clinic site and season of visit were used to estimate adjusted means of femoral measures and 95% confidence limits within quartiles of vitamin D. Tests of linear trend were performed for each femoral measure across increasing serum 25(OH)D levels. Femoral neck vBMD measures were all found to increase with increasing 25(OH)D level. Overall femoral neck size, represented by cross-sectional area and integral volume, did not vary by serum 25(OH)D level. However, both cortical volume and cortical volume as a percent of integral volume increased with increasing 25(OH)D level. Femoral shaft cortical area and percent cortical area were positively associated with serum 25(OH)D level, but the remaining femoral shaft measures did not demonstrate any association. These observed associations of femoral neck cortical and trabecular vBMD and percent cortical bone volume to serum 25(OH)D among elderly men suggest that higher serum vitamin D levels may inhibit endosteal resorption, independent of the effects of PTH.

Identifier

doi:10.6083/M42F7KFF

School

School of Medicine

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