CPAP and Glucose Metabolism in Non-Diabetic OSA Subjects

The purpose of the current study is to investigate whether alleviation of OSA by CPAP positively impacts glucose metabolism in non-diabetic patients.

Glucose metabolism in patients newly diagnosed with moderate-severe OSA and without diabetes will be monitored for two weeks prior to commencement of CPAP using a CGM. They will consume a 75g oral glucose drink fasted on waking twice during the two-week monitoring period, having consumed a standardised meal the evening prior. After establishing CPAP use for at least four weeks they will undergo the same protocol as for the observation period prior to commencing CPAP. Glucose metabolism will be monitored using an interstitial (skin based) glucose monitor.

Inclusion Criteria: 1. Community dwelling adult males and females aged 18-65 years 2. Polysomnography confirmed moderate to severe OSA with apnea hypopnea index (AHI) ≥15/hr within the past 60 months 3. Able to give written informed consent 4. Proficient in English 6\. Diagnosed non-diabetic as defined by the American Diabetes Association as any of the following recent (\<3 months) findings: 1. Fasting glucose with a BGL \<7.0 mmol/L 2. Glucose tolerance with a 2-hour BGL of \< 11.1 mmol/L after a formal 75g Oral Glucose Tolerance Test (OGTT) 3. HbA1C of ≤ 6.5% 7. Possession or regular access to a mobile telephone with capability to download and run the Withings Sleep Anlayser App. Exclusion Criteria: 1. Clinically significant co-morbidity (e.g. myocardial infarction, congestive heart failure, stroke, arrythmia, chronic kidney or liver disease, epilepsy, head injury) 2. Severe mental health disorders (e.g. current major depressive disorder, schizophrenia, bipolar disorder) that in the opinion of the investigator is not adequately treated or will significantly affect their participation in the study. 3. Regular (\>2 times per month) use of sleep-affecting medication (e.g. benzodiazepines, opioids, antidepressants) 4. Regular night shift work or travel overseas within the last 2 weeks 5. Sleep physician has advised against CPAP withdrawal 6. Pregnancy 7. Active smoking or routine alcohol use (more than 2 standard drinks a day) or excessive caffeine intake (\>300 mg a day) or recent (in the past month) use of illicit drugs 8. Current or previous diagnosis of diabetes mellitus (previous gestational diabetes mellitus not excluded) 9. Current or recent (\<3 months) use of hypoglycaemic agents 10. Undergoing a weight loss programme 11. Contraindications for use of the FreeStyle Libre Pro Sensor. E.g. Known hypersensitivity to skin adhesives such as those used to attach the sensor to the arm.