Rationale: Twenty-eight percent of people with mild to moderate obstructive sleep apnea experience daytime sleepiness, which interferes with daily functioning. It remains unclear whether treatment with continuous positive airway pressure improves daytime function in these patients.

Objectives: To evaluate the efficacy of continuous positive airway pressure treatment to improve functional status in sleepy patients with mild and moderate obstructive sleep apnea.

Methods: Patients with self-reported daytime sleepiness (Epworth Sleepiness Scale score >10) and an apnea-hypopnea index with 3% desaturation and from 5 to 30 events per hour were randomized to 8 weeks of active or sham continuous positive airway pressure treatment. After the 8-week intervention, participants in the sham arm received 8 weeks of active continuous positive airway pressure treatment.

Measurements and Main Results: The Total score on the Functional Outcomes of Sleep Questionnaire was the primary outcome measure. The adjusted mean change in the Total score after the first 8-week intervention was 0.89 for the active group (n = 113) and −0.06 for the placebo group (n = 110) (P = 0.006). The group difference in mean change corresponded to an effect size of 0.41 (95% confidence interval, 0.14–0.67). The mean (SD) improvement in Functional Outcomes of Sleep Questionnaire Total score from the beginning to the end of the crossover phase (n = 91) was 1.73 ± 2.50 (t[90] = 6.59; P < 0.00001) with an effect size of 0.69.

Conclusions: Continuous positive airway pressure treatment improves the functional outcome of sleepy patients with mild and moderate obstructive sleep apnea.

Clinical trial registered with www.clinicaltrials.gov (NCT 00127348).