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.The obstructive sleep apnoea syndrome (OSAS) is a common disorder defined by the occurrence of repeated episodes of upper airway obstruction and airflow cessation (apnoeas) that normally lead to arterial hypoxaemia and sleep disruption. 1 A number of clinical features, such as obesity, excessive daytime sleepiness (EDS) and insulin resistance (IR), are often but not invariably present in these patients.
2-7The relationship between obesity, IR and EDS in patients with OSAS is complex and poorly understood. [8][9][10] Obesity is generally regarded as a risk factor for both OSAS and IR.11 12 However, factors other than obesity appear to play a significant role in the development of IR and metabolic disturbances in patients with OSAS, 8 13-16 including sleep fragmentation, increased sympathetic activity and intermittent hypoxia.
17-21On the other hand, experimental evidence shows that intermittent hypoxaemia during sleep triggers neural damage to brain regions that promote and control wakefulness through a convergence of oxidative and inflammatory events that ultimately lead to neuronal cell loss and EDS. 22 23 In this study, we hypothesised that EDS in OSAS is associated with IR, independent of obesity, and that the abolishment of nocturnal apnoeas by continuous positive airway pressure (CPAP) therapy improves both EDS and IR. To test this hypothesis, we studied two groups of patients with OSAS (22 each) who were carefully matched for severity of OSAS, obesity and age, but who were clearly different in terms of the presence or ...