SAT0485 PERCENTAGE BODY FAT HAS A STRONGER ASSOCIATION WITH BONE MINERAL DENSITY AT THE HIP AND SPINE COMPARED TO BODY MASS INDEX

Abstract

Background:A decreased body mass index (BMI) is associated with poorer bone health, a decreased bone mineral density (BMD), and an increased fracture risk. Cardiovascular (CVS) data has shown that the waist:hip ratio is a more robust measurement for CVS outcomes than BMI (1). Waist:hip ratio has never been evaluated as an outcome measure for bone health. Dual-energy x-ray absorptiometry (DEXA) has the capacity to measure average percentage fat in the L1-L4 region and at the hip, and directly relates to the measurement of waist:hip ratio.Objectives:To evaluate the relationship between BMD and average percent fat in a cohort referred for DEXA scanning.Methods:We analysed data routinely collected from patients referred for DEXA between 2004 and 2010 at the Royal Lancaster Infirmary in the North of England. Data collected for these patients included DEXA scans of BMD at the left and right hip, and at the lumbar spine, as well as average percent far and other risk factors for osteoporosis, including the FRAX risk factors. We used only the measures collected at baseline (time of first scan). We modelled the T scores of the BMD measurements using a linear regression model including percentage fat and BMI as explanatory variables, and adjusting for gender, age at scan, and other known risk factors for osteoporosis, including the FRAX risk factors. BMI and average percent fat were standardised.Results:The number of patients included was 33037, (82% female). Results of both regression models are shown in table 1 below. We show the standardised effect size estimates for average percent fat and BMI.Anatomical locationEffect size estimate for average percent fat (95% confidence intervals)P valueEffect size estimate for BMI (95% confidence intervals)P valueLeft neck-0.156 (-0.171, -0.141)<0.001-0.0255 (-0.0441, -0.00701)0.00692Left total-0.225 (-0.241, -0.208)<0.001-0.0680 (-0.0882, -0.0477)<0.001Left Ward’s-0.181 (-0.196, -0.166)<0.001-0.0268 (-0.0456, -0.00813)0.00493Left trochanter-0.263 (-0.281, -0.246)<0.001-0.0667 (-0.0882, -0.0451)<0.001Right neck-0.139 (-0.154, -0.124)<0.001-0.0131 (-0.0317, 0.00549)0.167Right total-0.221 (-0.237, -0.204)<0.001-0.0611 (-0.0811, -0.0411)<0.001Right Ward’s-0.180 (-0.196, -0.165)<0.001-0.0193 (-0.0381, -0.000586)0.0433Right trochanter-0.261 (-0.278, -0.243)<0.001-0.0598 (-0.0810, -0.0386)<0.001Spine (averaged L1-L4)0.219 (0.195, 0.242)<0.001-0.00846 (-0.0379, 0.0206)0.563Conclusion:The analysis shows that average percent fat is a statistically significant predictor for BMD at different anatomical locations, and a larger predictor in comparison to BMI when evaluated in the same model. In the right hip neck and the spine, BMI was not predictive of changes in BMD. Higher average percent fat increases the BMD in the spine, compared to a decline at the hip. Further research is needed to characterise the relationship more precisely and identify whether there is a causal link.