Fat Fraction and Iron Concentration in Lumbar Vertebral Bone Marrow in the UK Biobank

Background: Vertebral bone marrow (VBM) plays a critical role in bone homeostasis and metabolic health. Alterations in VBM fat and iron composition have been linked to age-related metabolic and musculoskeletal disorders, yet remain underexplored in large population-based studies. Objectives: This study aimed to assess VBM adipose tissue and iron concentration in the UK Biobank imaging cohort (N = 26,524) using magnetic resonance imaging (MRI). Methods: VBM adipose tissue using two approaches: fat fraction (FF) measured from 2-point Dixon MRI images and proton density fat fraction (PDFF) from multi-echo MRI scans, along with iron concentration from multi-echo MRI images, were measured. Sex-specific relationships between VBM measures, anthropometric and lifestyle factors as well as disease status were explored using correlation and linear regression analyses. Results: VBM FF and PDFF were higher, whereas VBM iron concentration was lower in participants with osteoporosis and type-2 diabetes (T2D; p < 0.00016). VBM FF and PDFF were positively associated with visceral adipose tissue and T2D and were inversely associated with spine bone mineral density (BMD) and total muscle (p < 0.00016) in both sexes; however, positive associations with smoking were observed only in women. VBM iron concentration was significantly positively associated with visceral adipose tissue, spine BMD, and alcohol intake, but negatively associated with T2D in men only. Discussion: These findings enhance the understanding of VBM measures in metabolic health assessments, highlighting their role as potential indicators of metabolic and musculoskeletal health.