Insulin resistance and daytime sleepiness in patients with sleep apnoea

Background: Excessive daytime sleepiness (EDS), obesity and insulin resistance (IR) occur frequently in patients with obstructive sleep apnoea syndrome (OSAS). We hypothesised that in these patients, EDS is a marker of IR, independent of obesity. Methods: We studied 44 patients with OSAS ( 22 with and 22 without EDS) matched for age (+/- 5 years), body mass index (BMI +/- 3 kg/m(2)) and severity of OSAS (as determined by the apnoea-hypopnoea index (AHI)), and 23 healthy controls. Patients (n = 35) were re-examined after 3 months of effective therapy with continuous positive airway pressure ( CPAP). EDS was assessed by both subjective (Epworth Sleepiness Scale) and objective ( Multiple Sleep Latency Test) methods. IR was determined by the HOMA index. Serum levels of glucose, triglycerides, cholesterol, cortisol, insulin, thyrotropin, growth hormone and insulin-like growth factor I (IGF-I) were also determined. Results: Despite the fact that age, BMI and AHI were similar, patients with EDS had higher plasma levels of glucose (p < 0.05) and insulin (p < 0.01), as well as evidence of IR (p < 0.01) compared with patients without EDS or healthy controls. CPAP treatment reduced cholesterol, insulin and the HOMA index and increased IGF-1 levels in patients with EDS, but did not modify any of these variables in patients without EDS. Conclusion: EDS in OSAS is associated with IR, independent of obesity. Hence EDS may be a useful clinical marker to identify patients with OSAS at risk of metabolic syndrome.