Integrated Evaluation of CPAP Therapy in Type 2 Diabetic Patients with Sleep Apnea: Quality of Life and Effects on Metabolic Function and Inflammation in Outpatient Care

Background. Type 2 diabetes mellitus (T2D) and moderate-to-severe obstructive sleep apnea (OSA) commonly coexist and exacerbate poor glycemic control, systemic inflammation, and diminished quality of life (QoL). Although continuous positive airway pressure (CPAP) therapy has demonstrated metabolic and anti-inflammatory benefits, its real-world impact in Bulgarian outpatient settings—where CPAP costs are borne entirely by patients—has not been characterized. Objectives. To evaluate the effects of six months of CPAP therapy on glycemic control (hemoglobin A1c [HbA1c]), systemic inflammation (high-sensitivity C-reactive protein [hsCRP]), body mass index (BMI), lipid profile (low-density lipoprotein [LDL]), QoL (Short Form 36 Physical Component Summary [SF-36 PCS] and Mental Component Summary [SF-36 MCS]), and survival among Bulgarian outpatients with T2D and moderate-to-severe OSA. Methods. In this prospective, multicenter cohort study conducted from January 2022 to July 2023, 142 adults with established T2D and OSA (apnea–hypopnea index [AHI] ≥ 15) were enrolled at three outpatient centers in Bulgaria. Fifty-five patients elected to purchase and use home-based CPAP (intervention group), while 87 declined CPAP—either because of cost or personal preference—and continued standard medical care without CPAP (control group). All participants underwent thorough outpatient evaluations at baseline (month 0) and at six months, including measurement of HbA1c, hsCRP, BMI, fasting lipid profile (LDL), and patient-reported QoL, via the SF-36 Health Survey. Survival was tracked throughout follow-up. Results. After six months, the CPAP group experienced a significant reduction in HbA1c from a median of 8.2% (IQR 7.5–9.5%) to 7.7% (6.7–8.7%), p < 0.001, whereas the control group’s HbA1c decreased modestly from a median of 8.6% (IQR 7.9–9.4%) to 8.3% (7.6–9.1%); p < 0.001), with a significant between-group difference at follow-up (p = 0.005). High-sensitivity CRP in the CPAP arm fell from a median of 2.34 mg/L (IQR 1.81–3.41) to 1.45 mg/L (IQR 1.25–2.20), p < 0.001, while remaining unchanged in controls (p = 0.847). BMI in the CPAP group declined significantly from 28.6 kg/m2, IQR 26.6–30.6 to 28 kg/m2, IQR 25.6–29.2 (p < 0.001), compared to no significant change in controls (median 28.9 kg/m2), p = 0.599. LDL decreased in the CPAP group from a median of 3.60 mmol/L (IQR 3.03–3.89) to 3.22 mmol/L (IQR 2.68–3.48), p < 0.001, with no significant reduction in controls (p = 0.843). Within the CPAP arm, both SF-36 PCS and SF-36 MCS scores improved significantly from baseline (p < 0.001 for each), although between-group differences at six months did not reach statistical significance (PCS: 48 ± 10 vs. 46 ± 9, p = 0.098; MCS: 46, IQR 40–54 vs. 46, IQR 39–53, p = 0.291). All-cause mortality during follow-up included 2 events in the CPAP group and 11 events in the control group (log-rank p = 0.071). Conclusions. In Bulgarian outpatients with T2D and moderate-to-severe OSA, six months of CPAP therapy significantly improved glycemic control, reduced systemic inflammation, lowered BMI and LDL, and enhanced QoL, with a non-significant trend toward reduced mortality. These findings underscore the importance of integrating CPAP into multidisciplinary management despite financial barriers.