Fifty healthy, normotensive individuals (34 women) with a mean age of 44.3 +/- 13.2 yr and a mean body mass index of 27.1 +/- 5.4 kg/m2 were tested for the presence or absence of insulin resistance and sleep-disordered breathing. The hypothesis of this investigation was that insulin resistance is associated with sleep-disordered breathing. In vivo insulin action with determination of steady-state plasma glucose (SSPG) and insulin was measured using simultaneous intravenous infusion of somatostatin, glucose, and insulin via a Harvard pump. Determination of sleep-disordered breathing was performed through clinical assessment and portable nocturnal monitoring using a validated sleep apnea recorder. Individuals with > or = 10 hypoxic respiratory events per hour of sleep were significantly more insulin-resistant than subjects without sleep-breathing disorders. After adjusting the relationship between insulin resistance and sleep-disordered breathing for potential confounding variables, it was found that this relationship was entirely dependent on body mass.