Sleep, Obesity, and Metabolism in Normal and Overweight Subjects: Effects of CPAP on Glucose Metabolism

Type 2 diabetes mellitus is one of the most prevalent medical conditions, affecting a staggering 246 million people worldwide. Obstructive sleep apnea is a relatively common and often undiagnosed condition in the general population. Cross-sectional studies of clinic and population-based samples suggest that up to 40% of patients with obstructive sleep apnea have type 2 diabetes and up to 75% of patients with type 2 diabetes have obstructive sleep apnea. There is increasing evidence that the pathophysiological features of intermittent hypoxia and sleep fragmentation may be responsible for altering glucose homeostasis and worsening insulin sensitivity. The mechanisms through which obstructive sleep apnea impairs glucose metabolism are largely unknown. While intermittent hypoxemia and sleep fragmentation are likely to play an essential role, the relative contribution of each in the causal pathway remains to be determined. Moreover, whether the adverse effects of intermittent hypoxia and sleep fragmentation are mediated through an increase in sympathetic nervous system activity, alterations in corticotropic function, and/or systemic inflammation is not known. Furthermore, it remains to be determined whether positive pressure therapy for obstructive sleep apnea has salutary effects on glucose metabolism. Many of the available studies examining the effects of PAP on glucose tolerance and insulin sensitivity are plagued by small sample sizes, lack of a control group, and limited data on compliance with positive pressure therapy. The current study will assess, using a community-based sample, whether treatment of obstructive sleep apnea with positive pressure therapy will improve insulin sensitivity, as assessed by the frequently sample intravenous glucose tolerance test (primary outcome measure).