Prospective observational studies of medically stable adult patients with newly diagnosed previously untreated moderate to severe obstructive sleep apnoea were eligible for inclusion. Moderate to severe obstructive sleep apnoea was defined by an apnoea-hypopnoea index (AHI) of 15 or more. CPAP intervention durations were more than two weeks. Included studies were required to measure homeostasis model assessment insulin resistance (HOMA-IR) and BMI before and after CPAP. Study participants were required to be free from type 2 diabetes, any cardiovascular or cerebrovascular disease, liver, endocrine, inflammatory or other chronic disease at the time of diagnosis and to be without significant changes in dietary, BMI and medication use during the study.
The mean age of study participants ranged from 40 to 56 years. Mean baseline BMI ranged from 32 to 46.1kg/m². Mean baseline HOMA-IR ranged from 4.99 to 7.6. The mean baseline rate of apnoea-hypopnoea index events ranged from more than 15 to 91 per hour and the mean daily CPAP use ranged from four to six hours.
Two reviewers independently assessed studies for inclusion.