Continuous positive airway pressure treatment in patients with sleep apnoea: does it really improve glucose metabolism?

Obstructive Sleep Apnoea Syndrome (OSAS) is a common disorder, characterised by repetitive episodes of partial or complete obstruction of the upper airway during sleep and associated with increasing respiratory efforts. These perturbations lead, in turn, to oxyhaemoglobin desaturation, sleep fragmentation, and daytime symptoms, mainly excessive sleepiness. Accumulating evidence suggests that intermittent hypoxia and oxyhaemoglobin desaturation may result, independently of obesity, in impaired glucose metabolism, as well as insulin resistance even in non-diabetic patients with OSAS. Additionally, OSAS has been proposed as an independent risk factor for type 2 diabetes mellitus. Continuous Positive Airway Pressure (CPAP) is the treatment of choice for OSAS, since it eliminates upper airway collapse during sleep and also improves sleep fragmentation, daytime symptoms and quality of life. Moreover, it has been proposed that the amelioration of breathing disturbances during sleep can improve several markers of glucose metabolism and insulin resistance, such as glycated haemoglobin, fasting glucose, insulin, and insulin resistance. Indeed, some studies have reported improvements in these parameters especially in compliant patients. However, other works failed to confirm this beneficial effect. The present article reviews the issue whether CPAP treatment exerts a beneficial effect on glucose metabolism and insulin resistance.