Lower fat-free mass is independently linked to restless legs syndrome in men: a cross-sectional PSG-BIA study.

Objective: Restless legs syndrome (RLS) is a common sensorimotor disorder that disrupts sleep and quality of life. Sarcopenia-reduced skeletal muscle mass and function-has been linked to sleep disturbances, but its relationship with RLS remains unclear. We examined whether sarcopenia is associated with RLS, with a focus on sex-specific effects. Methods: We conducted a cross-sectional analysis of 5,752 adults who underwent both type-I polysomnography (PSG) and bioelectrical impedance analysis (BIA) at a tertiary sleep center. RLS was diagnosed by IRLSSG criteria. Sarcopenia was defined using skeletal muscle index (SMI) and fat-free mass index (FFMI) thresholds. Multivariable models adjusted for age, physical activity, caffeine/alcohol intake, and apnea-hypopnea index (AHI). Results: RLS prevalence was 6.6% in females and 2.9% in males. Sarcopenia was more frequent in the RLS group than in non-RLS (10.6 vs. 6.8%), particularly among males (8.7 vs. 3.2%). In males, lower SMI and FFMI were independently associated with higher odds of RLS; sex interaction for FFMI was significant. Conclusions: Reduced muscle mass is independently associated with RLS in men, suggesting a male-specific muscle phenotype relevant to RLS pathophysiology. Incorporating BIA-based screening and muscle-preserving interventions may benefit the management of male patients with RLS.