Long-term improvement of insulin sensitivity during CPAP therapy in the obstructive sleep apnoea syndrome.

Background: We recently demonstrated that continuous positive airway pressure (CPAP) therapy rapidly improves insulin sensitivity within 2 days in non-diabetic patients with obstructive sleep apnea syndrome. In these very patients we investigated whether this improvement of insulin sensitivity is maintained during long-term CPAP therapy.
Material/methods: After a mean of 2.9 years (963+/-98 days) of CPAP treatment, these patients were reevaluated and hyperinsulinemic euglycemic clamp studies were performed in those with regular and effective CPAP treatment.
Results: From the initial 31 patients 16 could be reevaluated. 4 patients did not use their devices regularly (CPAP usage <2.5 h/night), 2 patients had insufficient CPAP treatment (AHI > or =10/h). One patient had developed type 2 diabetes mellitus. In the remaining 9 patients who used their devices regularly and effective (mean CPAP usage 5.2+/-1.6 h/night, mean AHI 3.3+/-2.6/h), mean insulin sensitivity index (ISI) was significantly higher than the baseline ISI established 2.9 years before (10.6+/-7.0 vs. 6.3+/-5.6 micromol/kg x min; p=0.008). At baseline 7 out of 9 patients had an impaired fasting glucose, after 2.9 years of treatment 3 out of 9 patients still had an impaired fasting glucose. The mean body mass index (BMI) had remained unchanged (31.4+/-7.8 vs. 31.4+/-7.6 kg/m2; mean individual difference -0.02+/-1.9 kg/m2).
Conclusions: OSA is a risk factor for impaired insulin sensitivity. CPAP treatment, when used regularly and with effective pressure, may improve insulin sensitivity over long time.