Sleep apnoea and the hypothalamic–pituitary–adrenal axis in men and women: effects of continuous positive airway pressure

Previous findings on the association of obstructive sleep apnoea (OSA) and the hypothalamic–pituitary–adrenal (HPA) axis are inconsistent, partly due to the confounding effect of obesity and infrequent sampling. Our goal was to examine whether in a relatively nonobese population, OSA is associated with elevated cortisol levels and to assess the effects of a 2-month placebo-controlled continuous positive airway pressure (sham-CPAP) use. 72 subjects (35 middle-aged males and post-menopausal females with OSA, and 37 male and female controls) were studied in the sleep laboratory for four nights. 24-h blood sampling was performed every hour on the fourth day and night in the sleep laboratory at baseline, after sham-CPAP and after CPAP treatment. In both apnoeic men and women, OSA was associated with significantly higher 24-h cortisol levels compared with controls, whereas CPAP lowered cortisol levels significantly, close to those of controls. These results suggest that OSA in nonobese men and slightly obese women is associated with HPA axis activation, similar albeit stronger compared with obese individuals with sleep apnoea. Short-term CPAP use decreased cortisol levels significantly compared with baseline, indicating that CPAP may have a protective effect against comorbidities frequently associated with chronic activation of the HPA axis, e.g. hypertension.