Fibroblast Growth Factor 23 is Associated With Adiposity in Patients Receiving Hemodialysis: Possible Cross Talk Between Bone and Adipose Tissue

Objective: Fibroblast growth factor 23 (FGF-23) may be involved in signaling between bone and adipose tissue in dialysis patients, but its role is uncertain. We sought to examine the association between FGF-23 and adiposity and whether this association is mediated in part by leptin. Design/Setting: We performed univariate and multivariate linear regression analyses using data from 611 participants in a cohort of prevalent hemodialysis patients recruited from dialysis centers in Atlanta, GA and San Francisco, CA from 2009 to 2011. We also investigated the role of leptin in these relationships. Subjects: Participants were aged ≥18 years, English or Spanish speaking, and receiving hemodialysis for at least 3 months. Main Outcome Measures: Outcome measures of adiposity included body mass index, waist circumference, and body fat measured by bioelectrical impedance spectroscopy. Results: Mean age was 56 ± 14 years, 39.8% were female, and median serum FGF-23 was 807 pg/mL. In fully adjusted models, FGF-23 was inversely associated with body mass index (−0.24 kg/m² per 50% higher FGF-23, 95% confidence interval [CI]: −0.38 to −0.10), waist circumference (−0.44 cm per 50% higher FGF-23, 95% CI: −0.79 to −0.08), and percent body fat (−0.58% per 50% higher FGF-23, 95% CI: −0.79 to −0.37). Leptin was inversely associated with FGF-23. Addition of leptin to body composition models attenuated the associations between FGF-23 and measures of adiposity, but FGF-23 remained significantly associated with percent body fat (−0.17% per 50% higher FGF-23, 95% CI: −0.32 to −0.02). Conclusion: We found a negative association between FGF-23 and adiposity that appears to be mediated in part by leptin. As adipose tissue provides a “protective energy depot” for patients with chronic illness, a decrease in adipose tissue may be one mechanism in which higher FGF-23 levels may contribute to increased mortality in dialysis patients.