The potential role of interleukin-6 in the association between inflammation and cognitive performance in obstructive sleep apnea

Background: Interleukin-6 (IL-6) represents one of the main molecules involved in inflammatory responses, which can be altered in either patients with cognitive impairment or obstructive sleep apnea (OSA). The present study aimed to evaluate serum IL-6 levels and cognitive performance in patients with severe OSA (Apnea-Hypopnea Index - AHI >30/h). Methods: Thirty patients with severe OSA were compared to 15 controls similar in age, sex, and Body Mass Index. All patients underwent a sleep medicine interview, including the Epworth Sleepiness Scale (ESS), a polygraphic cardiorespiratory recording, the Montreal Cognitive Assessment (MoCA), and a blood sample for serum IL-6 assessment. Results: OSA patients presented higher IL-6 serum levels (Md = 7.38) than controls (Md = 2.20, p < 0.001). Moreover, OSA patients showed lower MoCA (Md = 27.00) and higher ESS scores (Md = 8.00) than controls (Md = 30.00, p <0.001; Md = 4.00, p = 0.004, respectively). Higher IL-6 serum levels were associated with lower oxygen saturation parameters and MoCA scores. Conclusions: This study documented an association between inflammation, featured by higher IL-6 serum levels, and both nocturnal hypoxemia and cognitive impairment in OSA patients. Therefore, the increase in IL-6 levels may represent the result of vascular damage and neuroinflammation due to intermittent nocturnal hypoxia and further causing neurocognitive dysfunction in OSA.