Twelve-Month CPAP Therapy Modulates BDNF Levels in Patients with Severe Obstructive Sleep Apnea: Implications for Metabolic and Treatment Compliance

Brain-derived neurotrophic factor (BDNF) is a neurotrophin involved in the regulation of synaptic plasticity and metabolic processes, including glucose metabolism and insulin sensitivity. In patients with obstructive sleep apnea (OSA), recurrent episodes of intermittent hypoxia may stimulate BDNF expression as a compensatory neuroprotective response. OSA is associated with metabolic disturbances, such as increased insulin resistance and a higher risk of type 2 diabetes. Continuous positive airway pressure (CPAP) therapy may influence both BDNF levels and metabolic outcomes. The aim of this study was to evaluate changes in BDNF concentration and glucose metabolism in patients with OSA, with particular emphasis on the effect of long-term CPAP therapy. Sixty-six adult patients with OSA confirmed by polysomnography were enrolled and divided into severe (s-OSA) and non-severe (ns-OSA) groups. Fasting blood samples were collected to measure glucose, insulin, and BDNF concentrations. Patients with s-OSA were re-evaluated after 12 months of CPAP therapy and further classified as compliant (sc-OSA) or non-compliant (snc-OSA) based on recorded device usage. The same biochemical parameters were assessed after the 12-month follow-up. Baseline BDNF levels were significantly higher in the s-OSA group compared to the ns-OSA group (20.1 ng/mL vs. 8.1 ng/mL, <i>p</i> = 0.02) and correlated with the apnea-hypopnea index (AHI, r = 0.38, <i>p</i> = 0.02). In the nsc-OSA group, BDNF concentrations increased significantly after 12 months (16.2 ng/mL vs. 35.5 ng/mL, <i>p</i> < 0.001), while no significant change was observed in the sc-OSA group (24.4 ng/mL vs. 27.4 ng/mL, <i>p</i> = 0.33). Among sc-OSA patients, a significant improvement in insulin resistance was noted, although no significant changes were observed in fasting glucose or insulin levels. Increased BDNF levels were observed in patients with s-OSA compared to ns-OSA. Compliant CPAP therapy was associated with reduced insulin resistance and no further BDNF increase, in contrast to non-compliance, suggesting a beneficial effect of CPAP on glucose metabolism and BDNF regulation. These findings support the hypothesis that both neurotrophic and metabolic responses in OSA may be modulated by disease severity and therapy adherence.