A Controlled Trial of CPAP Therapy on Metabolic Control in Individuals with Impaired Glucose Tolerance and Sleep Apnea

Study Objectives: To address whether treatment of sleep apnea improves glucose tolerance. Design: Randomized, double-blind crossover study. Setting: Sleep clinic referrals. Patients: 50 subjects with moderate to severe sleep apnea (AHI > 15) and impaired glucose tolerance. Interventions: Subjects were randomized to 8 weeks of CPAP or sham CPAP, followed by the alternate therapy after a one-month washout. After each treatment, subjects underwent 2-hour OGTT, polysomnography, actigraphy, and measurements of indices of glucose control. Measurements and Results: The primary outcome was normalization of the mean 2-h OGTT; a secondary outcome was improvement in the Insulin Sensitivity Index (ISI (0,120). Subjects were 42% men, mean age of 54 (10), BMI of 39 (8), and AHI of 44 (27). Baseline fasting glucose was 104 (12), and mean 2-h OGTT was 110 (57) mg/dL. Seven subjects normalized their mean 2-h OGTT after CPAP but not after sham CPAP, while 5 subjects normalized after sham CPAP but not after CPAP. Overall, there was no improvement in ISI (0,120) between CPAP and sham CPAP (3.6%; 95% CI: [-2.2%, 9.7%]; P = 0.22). However, in those subjects with baseline AHI >= 30 (n = 25), there was a 13.3% (95% CI: [5.2%, 22.1%]; P < 0.001) improvement in ISI (0,120) and a 28.7% (95%CI: [-46.5%, -10.9%], P = 0.002) reduction in the 2-h insulin level after CPAP compared to sham CPAP. Conclusions: This study did not show that IGT normalizes after CPAP in subjects with moderate sleep apnea and obesity. However, insulin sensitivity improved in those with AHI >= 30, suggesting beneficial metabolic effects of CPAP in severe sleep apnea.