P119 Average percent fat is associated with decreased bone mineral density at the hip but increase at the spine longitudinally, where weight shows a positive association at all anatomical locations
Authors: Thurston Charles , Kerns Jemma , Dondelinger Frank , Hale Alison , Bukhari Marwan 
Published: April 2021

Abstract
Background/Aims
Body composition changes are associated with changes in bone mineral density (BMD). Composite measures of body compartments, such as weight and body mass index (BMI) have a positive association with BMD. The aim was to study average percent fat from dual energy X-ray absorptiometry (DEXA) as a potentially useful clinical measurement.
Methods
BMD data in grams/cenitmetre2 was collected from DEXA scans after referral from secondary care to the Royal Lancaster Infirmary from 2004-2010. BMD data related to the left and right hip (the neck, Ward’s area, trochanter, and total hip), and the spine (L1-L4) was measured. Data was collected longitudinally, and BMD in g/cm2 was modelled at the regions of the hip and spine using mixed effects linear models. Average percent fat and weight (kg) were used as explanatory variables, whilst adjusting for age at scan, gender, and other risk factors such as FRAX risk factors.
Results
7910 patients (88% female) were included, all with average percent fat and weight measurements. The results of the models (Table 1) all have a P value&lt;0.05. Average percent fat had a significant negative association at all regions of the left and right hip, but a significant positive association at the spine. Weight showed a significant positive association with BMD at the hip and spine. P119 Table 1:Effect size estimates from mixed effects models of BMD at regions of the hip, and the spine.Anatomical locationEffect size estimate for average percent fat (95% confidence intervals)Effect size estimate for weight (95% confidence intervals)Left neck-6.63x10-4 (-9.69x10-4, -3.56x10-4)2.07x10-3 (1.91x10-3, 2.23x10-3)Left total-1.03x10-3 (-1.32x10-3, -7.41x10-4)3.45x10-3 (3.29x10-3, 3.61x10-3)Left Ward’s-1.07x10-3 (-1.38x10-3, -7.65x10-4)1.85x10-3 (1.69x10-3, 2.02x10-3)Left trochanter-1.15x10-3 (-1.46x10-3, -8.47x10-4)3.65x10-3 (3.48x10-3, 3.81x10-3)Right neck-6.91x10-4 (-9.94x10-4, -3.88x10-4)1.97x10-3 (1.81x10-3, 2.14x10-3)Right total-1.19x10-3 (-1.48x10-3, -8.96x10-4)3.39x10-3 (3.23x10-3, 3.55x10-3)Right Ward’s-1.07x10-3 (-1.38x10-3, -7.65x10-4)1.85x10-3 (1.69x10-3, 2.02x10-3)Right trochanter-1.19x10-3 (-1.52x10-3, -8.72x10-4)3.65x10-3 (3.39x10-3, 3.73x10-3)Spine (averaged L1-L4)1.76x10-3 (1.46x10-3, 2.05x10-3)1.42x10-3 (1.16x10-3, 1.68x10-3)
Conclusion
The negative association seen with average percent fat at the hip could reflect the potential negative endocrine effects of fat, and the effect of localized inflammation at the hip. Increased adiposity is also linked to sarcopenia, and further body compositional changes. However, the potential negative effects of increased adiposity at the abdomen and spine are potentially overridden by the increased biomechanical loading generated by the increased adiposity, highlighted by weight’s positive association with BMD at the spine. The average percent fat results are not mirrored with weight at the hip. This highlights that composite measures are not specific enough to measure changes in body composition compartments, and their resulting change in risk related to BMD.
Disclosure
C. Thurston: None. J. Kerns: None. F. Dondelinger: None. A. Hale: None. M. Bukhari: None.