Abstract

Objective: Low body mass index (BMI) is a known risk factor for osteoporosis and is part of the FRAX™ 10-year fracture risk stratification tool for predicting fragility fractures. Little is known regarding the effects of changing body composition on bone mineral density (BMD). However, increasing fat mass (FM) improves BMD in young women with anorexia nervosa. This study aimed to assess whether changes in FM over time affected BMD in the general population.

Material and Methods: Data was collected from patients who underwent dual-energy X-ray absorptiometry (DEXA) assessment between 2004 and 2011. Patients were included if they had multiple scans, including FM measurements. Our scanners limited these to scans of the lumbar spine. Linear regression analysis was performed to identify the relationship between changes in FM and BMD. Backwards stepwise linear regression analysis was performed to identify confounding factors, including sex, risk factors, previous fractures, and baseline BMI.

Results: In this study, 23,239 patients were included, of which 702 met the inclusion criteria. There were 609 (86%) females and 93 (13%) males with a mean age of 64.5 (SD 11.2) years at first scan. We identified a strong positive correlation between increasing FM and BMD between scans (coefficient 28.4; p<0.01; 95% CI, 26.6–30.1). Previous pelvic and femur fractures and a history of inflammatory diseases were also associated with increasing FM (p<0.05). This relationship was true regardless of patients BMI at their first scan.

Conclusion: These findings suggest that patients at high risk of fragility fractures should be encouraged to increase their FM as long as they are at a low risk for disease states related to high FM.