Background: Sleep plays a fundamental role in maintaining autonomic homeostasis. Disturbances in sleep quality have been implicated in altered cardiovascular regulation, yet objective evaluation of autonomic function in relation to subjective sleep assessment remains limited. The present study examined the association between sleep quality and autonomic nervous system function in apparently healthy adults. Material and Methods: This analytical cross-sectional study included 186 adults aged 20–50 years. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). Participants were categorized as good sleepers (PSQI ≤5; n = 112) and poor sleepers (PSQI >5; n = 74). Autonomic function was evaluated through short-term heart rate variability (HRV) analysis (time- and frequency-domain parameters) and standard cardiovascular reflex tests (deep breathing, active standing, and isometric handgrip). Intergroup comparisons were performed using appropriate statistical tests, and correlations between PSQI score and autonomic parameters were analyzed. Results: Poor sleepers exhibited significantly higher body mass index (25.3 ± 3.4 vs 24.1 ± 3.0 kg/m²; p = 0.021), systolic (120.7 ± 10.3 vs 116.9 ± 8.8 mmHg; p = 0.008) and diastolic blood pressure (78.7 ± 7.1 vs 75.5 ± 6.2 mmHg; p = 0.004), and resting heart rate (77.6 ± 9.1 vs 72.1 ± 7.6 beats/min; p < 0.001). Time-domain HRV indices were significantly reduced in poor sleepers (SDNN: 36.5 ± 10.8 vs 48.7 ± 12.3 ms; RMSSD: 29.8 ± 11.2 vs 42.9 ± 14.1 ms; p < 0.001). HF power was lower (342.7 ± 156.9 vs 528.3 ± 198.4 ms²; p < 0.001), whereas LF/HF ratio was higher (2.12 ± 0.63 vs 1.28 ± 0.42; p < 0.001). Poor sleepers also demonstrated reduced E:I ratio and exaggerated sympathetic responses during orthostatic and handgrip testing (p < 0.001). PSQI score correlated negatively with SDNN (r = −0.46), RMSSD (r = −0.51), and HF power (r = −0.48), and positively with LF/HF ratio (r = 0.54) (p < 0.001). Conclusion: Poor sleep quality is associated with reduced vagal modulation and relative sympathetic predominance, indicating subclinical autonomic imbalance in otherwise healthy adults.

Sleep quality; Heart rate variability; Autonomic function; Sympathovagal balance; Pittsburgh Sleep Quality Index