A recent study published in BMJ Open has revealed that the fat-to-muscle ratio (FMR) is significantly associated with secondary osteoporosis (OP) in patients with rheumatoid arthritis (RA). The study enrolled 670 hospitalized RA patients and 126 healthy controls at a tertiary hospital in eastern China between October 2019 and October 2022.
Analysis indicated that RA patients had markedly reduced total skeletal muscle mass (19.49 vs 25.38, p<0.001), hip bone mineral density (BMD) (0.90 vs 1.15, p<0.001), and L1–4 BMD (0.86 vs 1.08, p<0.001) compared with healthy controls. In contrast, RA patients exhibited increased total fat mass (18.33 vs 16.37, p=0.020) and elevated FMR (0.98 vs 0.68, p<0.001). The RA cohort presented with a median disease activity score in 28 joints (DAS28) of 5.03, rheumatoid factor (RF) of 104.75, C-reactive protein of 25.65, and erythrocyte sedimentation rate (ESR) of 59.00.
Body composition parameters showed notable correlations with disease activity markers. Total fat mass positively correlated with both the simplified disease activity index (SDAI) and clinical disease activity index (CDAI) (p<0.001), while total skeletal muscle mass correlated negatively with ESR (p=0.001) and positively with both L1–4 and hip BMD (p<0.001). FMR exhibited a positive correlation with CDAI (p<0.001). Significant differences in total fat mass and FMR were observed among RA patients stratified by disease activity levels (p<0.001).
Patients with concomitant OP or those receiving glucocorticoid therapy demonstrated higher total fat mass and FMR, alongside lower skeletal muscle mass (p<0.01). Logistic regression and four machine learning algorithms identified age and FMR as key predictors of secondary OP. Subgroup analysis revealed an interaction between FMR and gender, and dose-response analysis confirmed a consistent relationship between FMR and OP risk.
Supporting these findings, a study published in Scientific Reports examined postmenopausal women with OP and found that fat mass positively correlated with both cognitive function and BMD. The study concluded that fat mass is an important indicator of body composition in postmenopausal women and should be considered in monitoring and intervention strategies.
These findings suggest that FMR may serve as a clinically useful indicator for secondary OP in RA patients. Monitoring FMR, alongside other risk factors, could help identify patients at higher risk and support more comprehensive disease management and comorbidity prevention. However, prospective validation of the diagnostic performance is needed before this metric can be widely implemented in clinical practice.
References
- Shi JT, Xia XX, Xing QX, Chu YR, Wang JX, Xu SQ. Association between fat-to-muscle ratio and secondary osteoporosis in rheumatoid arthritis: a cross-sectional study at a tertiary hospital in China. BMJ Open. 2025 Sep 21;15(9):e101576.
- Zhang, D., Zhu, Z., Xue, L. et al. Fat mass in postmenopausal women with osteoporosis is associated with cognitive function. Sci Rep 15, 18079 (2025).