Effect of CPAP on insulin resistance and HbA1c in men with obstructive sleep apnoea and type 2 diabetes

Background: The effects of continuous positive airway pressure ( CPAP) for obstructive sleep apnoea (OSA) on insulin resistance are not clear. Trials have found conflicting results and no appropriate control groups have been used. Methods: Forty-two men with known type 2 diabetes and newly diagnosed OSA (. 10 dips/h in oxygen saturation of >4%) were randomised to receive therapeutic ( n = 20) or placebo CPAP ( n = 22) for 3 months. Baseline tests were performed and repeated after 3 months. The study was double blind. Results: Results are expressed as mean (SD). CPAP improved the Epworth sleepiness score significantly more in the therapeutic group than in the placebo group ( -6.6 (4.5) vs 22.6 (4.9), p = 0.01). The maintenance of wakefulness test improved significantly in the therapeutic group but not in the placebo group (+10.6 (13.9) vs 24.7 (11.8) min, p = 0.001). Glycaemic control and insulin resistance did not significantly change in either the therapeutic or placebo groups: HbA1c ( 20.02 (1.5) vs + 0.1 (0.7), p = 0.7, 95% CI 20.6% to + 0.9%), euglycaemic clamp ( M/I: + 1.7 (14.1) vs 25.7 (14.8), p = 0.2, 95% CI 21.8 to + 0.3 I/kg/ min(1000)), HOMA-% S ( -1.5 (2.3) vs -1.1 (1.8), p = 0.2, 95% CI -0.3% to + 0.08%) and adiponectin ( -1.1 (1.2) vs -1.1 (1.3), p = 0.2, 95% CI -0.7 to + 0.6 mu g/ml). Body mass index, bioimpedance and anthropometric measurements were unchanged. Hours of CPAP use per night were 3.6 (2.8) in the treatment group and 3.3 (3.0) in the placebo group ( p = 0.8). There was no correlation between CPAP use and the measures of glycaemic control or insulin resistance. Conclusion: Therapeutic CPAP does not significantly improve measures of glycaemic control or insulin resistance in men with type 2 diabetes and OSA.