Background/Objectives: Factors underlying excessive daytime sleepiness (EDS) in obstructive sleep apnea (OSA) are not fully understood. We investigated whether polysomnography (PSG) parameters differed between non-sleepy and sleepy (based on the Epworth Sleepiness Scale (ESS)) OSA patients with the same disease severity, which may play a role in the presence of EDS. Methods: A total of 1307 patients, without cardiovascular, metabolic, respiratory, or inflammatory comorbidities, diagnosed with OSA (apnea–hypopnea index (AHI) ≥ 5 per hour of sleep) with type 1 PSG were included. Based on the AHI, patients were classified into mild- (AHI 5–14.9, n = 236), moderate- (AHI 15–29.9, n = 367), and severe-OSA (AHI ≥ 30, n = 704) groups. These groups were further divided into two subgroups based on the ESS, the most convenient and widely used tool to assess excessive daytime sleepiness: sleepy (ESS > 10) and non-sleepy (ESS ≤ 10). PSG data were compared between groups, and multivariable logistic regression was used to identify differences after adjustment for confounders. Results: For the entire population, male sex, younger age, obesity, depression, increased wakefulness after sleep onset (WASO), the arousal index, shorter sleep latency, and all indices of OSA severity (AHI, oxygen desaturation index, mean and lowest resting room air pulse oximetry (SpO₂), and sleep time with oxygen saturation < 90% (TST90)) were significantly associated with EDS. The arousal index consistently showed a strong association with EDS across all OSA severity groups. Moderate-OSA sleepy patients were younger, with shorter sleep latency and increased indices of OSA severity, excluding the AHI. Severe-OSA sleepy patients were younger, males, and obese; had depression, decreased slow-wave sleep (SWS) and sleep latency, and increased WASO; and presented an increase in all indices of OSA severity. Conclusions: Our results suggest that male sex, younger age, obesity, the presence of depression, WASO, lower sleep efficiency, the arousal index, and all indices of OSA severity may account for the presence or absence of EDS in OSA patients and could be useful for exploring the underlying pathophysiological mechanisms for precision medicine.

Background: There are limited data on the association between B12 levels, objective sleep quality, and cardiovascular disease in patients with obstructive sleep apnoea (OSA). Therefore, the aim of our study was to assess vitamin B12 levels in a sleep clinic population in Crete, Greece, and investigate possible correlations with polysomnographic parameters and prevalent cardiovascular disease (CVD). Methods: In this cross-sectional study, data from 1468 recruited patients with OSA from the clinical database of the Sleep Disorders Center, Department of Respiratory Medicine, School of Medicine, University of Crete, were analyzed. OSA was defined as an apnoea–hypopnoea index ≥ 5 events per hour of sleep after type-1 Polysomnography (PSG). Data regarding anthropometrics, socio-demographics, and medical history was obtained. Logistic regression analysis was applied to examine the effect of vitamin B12 levels on PSG parameters and prevalent CVD after controlling for potential explanatory variables, including age, gender, obesity, smoking status, and co-morbidities. Results: The median vitamin B12 was 380.5 (301, 490) pg/mL. After adjustments, Vitamin B12 levels < 380.5 were associated with 24% higher odds of prolonged sleep latency (≥40 min) prevalence (OR = 1.240, 95% CI = 1.005–1.531, p = 0.045) and alterations in the proportion of NREM and REM sleep stages with 2.3 times higher likelihood of elevated NREM sleep > 80% of total sleep time (OR = 2.312, 95% CI = 1.049–5.096, p = 0.038) and 2.9 times higher likelihood of low REM sleep < 20% of total sleep time (OR = 2.858, 95% CI = 1.197–6.827, p = 0.018). Moreover, Vitamin levels < 380.5 were significantly associated with a 59.9% increase in the odds of prevalent CVD (OR = 1.599, 95% CI = 1.035–2.471, p = 0.034). Conclusions: In conclusion, our results suggest that vitamin B12 status may be associated with impaired objective sleep quality in OSA patients, potentially influencing prevalent CVD. However, further prospective research is needed to establish causality and elucidate the potential underlying mechanisms that could link vitamin B12 levels to various sleep parameters and cardiovascular disease in patients with OSA.