The Association between Rheumatoid Arthritis, Bone Strength, and Body Composition within the Women's Health Initiative

Abstract

Introduction: Osteoporotic fractures, a major public health problem in aging populations, can lead to increased disability and mortality. Though rheumatoid arthritis (RA) patients have a higher risk for fractures than healthy populations, it is not known how hip structural geometry and body composition, two factors associated with bone strength, affect fracture risk in this population. The overall goal of this dissertation is to examine the association between RA, fracture, hip structural geometry, and body composition, in the participants of the Women's Health Initiative (WHI).Methods: The association between probable RA and fracture risk was tested using the entire WHI cohort (n=161,808). The association between probable RA and hip structural geometry was tested, both cross-sectionally and longitudinally, in a smaller sample (n=11,020) of participants from the WHI Bone Density Centers (WHI-BMD). The last study, testing the association between probable RA and body composition was also conducted in the WHI-BMD cohort.Results: In comparison to the non-arthritic group, the probable RA group had a significant 50%, 2-fold, and 3-fold increase in any, spine, and hip fracture, respectively. The association was not mot modified by age or ethnicity, but glucocorticoid use altered the association between RA and spine fractures. In terms of geometry, the probable RA had a significantly lower (p<0.05) mean hip BMD, outer diameter, cross-sectional area, and section modulus at the narrow neck region compared to control groups, indicating reduced bone strength. Body composition changes were present between the probable RA and the control group, with the probable RA group having statistically lower estimate of lean mass and statistically higher estimates of fat mass compared to the non-arthritic control group cross-sectionally and over the study.Conclusion: These studies confirm the increased risk for fracture among RA patients, while providing evidence that RA alters bone strength, especially at the hip, and negatively effects body composition by reducing lean mass and increasing fat mass. Additional research is needed link structural geometry and body composition to bone strength to lead to tailored interventions to minimize decreases in bone strength in this high fracture risk population.