Despite evidence of a relationship among obstructive sleep apnea (OSA), metabolic dysregulation, and diabetes, it is uncertain whether OSA treatment can improve metabolic parameters. We sought to determine effects of long-term continuous positive airway pressure (CPAP) treatment on glycemic control and diabetes risk in patients with cardiovascular disease (CVD) and OSA. RESEARCH DESIGN AND METHODSBlood, medical history, and personal data were collected in a substudy of 888 participants in the Sleep Apnea cardioVascular Endpoints (SAVE) trial in which patients with OSA and stable CVD were randomized to receive CPAP plus usual care, or usual care alone. Serum glucose and glycated hemoglobin A 1c (HbA 1c ) were measured at baseline, 6 months, and 2 and 4 years and incident diabetes diagnoses recorded. RESULTSMedian follow-up was 4.3 years. In those with preexisting diabetes (n 5 274), there was no significant difference between the CPAP and usual care groups in serum glucose, HbA 1c , or antidiabetic medications during follow-up. There were also no significant between-group differences in participants with prediabetes (n 5 452) or new diagnoses of diabetes. Interaction testing suggested that women with diabetes did poorly in the usual care group, while their counterparts on CPAP therapy remained stable. CONCLUSIONSAmong patients with established CVD and OSA, we found no evidence that CPAP therapy over several years affects glycemic control in those with diabetes or prediabetes or diabetes risk over standard-of-care treatment. The potential differential effect according to sex deserves further investigation.Obstructive sleep apnea (OSA) is characterized by repeated episodes of upper-airway collapse during sleep that causes intermittent hypoxemia, sleep fragmentation, and daytime sleepiness. The standard therapy for OSA is continuous positive airway pressure (CPAP) to prevent airway obstruction (1).OSA is common in the population and strongly associated with obesity (2). Prospective cohort studies have found associations between moderate to severe OSA and

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