Sleepiness and Vitamin D Levels in Patients with Obstructive Sleep Apnea

Study Objectives: The aim of this cross-sectional study is to explore the association between serum 25-hydroxyvitamin D [25(OH)D] levels, a marker of Vitamin D status, and excessive daytime sleepiness (EDS), expressed as increased scores of the Epworth Sleepiness Scale (ESS), in a group of prospectively enrolled patients with obstructive sleep apnea (OSA). Methods: Newly diagnosed patients with OSA, divided into two groups, those with EDS (ESS > 10) and those without EDS (ESS < 10). All patients underwent night polysomnography. Measurement of serum 25(OH)D vitamin was performed using a radioimmunoassay. Results: In total, 217 patients with OSA (197 males and 20 females) were included. Patients with EDS had higher AHI (p < 0.001) values and lower mean serum 25(OH)D levels, compared with those of non-somnolent patients [17.4 (12.2-25.7) versus 21.1 (15.3-28.8) ng/mL, respectively, p = 0.005]. In patients with EDS, serum 25(OH)D levels correlated with average oxyhemoglobin saturation during sleep (r = 0.194, p = 0.043), and negatively with ESS score (r = -0.285, p = 0.003), AH Iota (r = -0.197, p = 0.040) and arousal index (r = -0.256, p = 0.019). Binary regression analysis identified Vit D serum levels (beta = -0.045, OR: 0.956, 95% CI: 0.916-0.997, p = 0.035), total sleep time (beta = 0.011, OR: 1.011, 95% CI: 1.002-1.021, p = 0.016) and AHI (beta = 0.022, OR: 1.022, 95% CI: 1.003-1.043, p = 0.026) as independent predictors of EDS in patients with OSA. In patients with EDS, multiple regression analysis indicated that ESS score was negatively associated with Vit D serum levels (beta = -0.135, p = 0.014) and minimum oxyhemoglobin saturation during sleep (beta = -0.137, p = 0.043). Conclusions: In the present study, EDS in patients with OSA is associated with low levels of Vitamin D, while sleep hypoxia may play a role in this process.