Vitamin D and Mean Platelet Volume as Biomarkers in Pediatric Obstructive Sleep Apnea: Associations with Disease Severity and Sleep Parameters.

Background/Objectives: Vitamin D and mean platelet volume (MPV) have been suggested as biomarkers of obstructive sleep apnea (OSA) in adults, while pediatric data remain limited. We aimed (i) to investigate associations between vitamin D and MPV with the presence and severity of pediatric OSA and (ii) to explore potential associations between vitamin D status and sleep parameters in normal-weight affected children. Methods: A total of 138 children with polysomnography-confirmed OSA and 138 age- and sex-matched controls were enrolled. All participants underwent detailed clinical, biochemical, and overnight sleep assessments. The OSA group was stratified according to disease severity. Results: Vitamin D levels were significantly lower in OSA patients (p < 0.0001), while MPV, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) were significantly higher (all p < 0.0001) than in the controls. Severe OSA was associated with elevated inflammation markers, higher insulin resistance, and lower vitamin D levels (all p < 0.0001). Vitamin D levels were inversely associated with the Apnea-Hypopnea Index (AHI) (R 0.37, adjusted r2 0.13, p < 0.0001) and Oxygen Desaturation Index (ODI) (R 0.36, adjusted r2 0.13, p < 0.0001), even after adjustments (both p < 0.0001). N1 and REM sleep were negatively associated with vitamin D in the OSA group (p = 0.01 and p = 0.02, respectively). Vitamin D deficiency was independently associated with higher odds of OSA (adjusted OR = 6.76, 95% CI: 3.97-11.51, p < 0.0001). Similarly, OSA presence was associated with lower vitamin D levels (aOR = 1.40, 95% CI: 1.06-1.94, p = 0.03). Conclusions: Vitamin D and MPV are associated with the presence and severity of pediatric OSA. Vitamin D levels were related to specific sleep architecture parameters, and MPV appeared to reflect inflammation associated with OSA, supporting their potential utility as biomarkers in pediatric OSA.