Early gain in body mass with continuous positive airway pressure therapy for obstructive sleep apnea

Abstract

Many clinicians believe that continuous positive airway pressure (CPAP) therapy of obstructive sleep apnea (OSA) is associated with a decrease in body mass, but to date, studies generally suggest long-term stability in body mass after 1 year. We have seen body mass increase after 4 weeks of treatment with CPAP in most patients with OSA. In this study, we test the hypothesis that therapy of OSA with CPAP produces a short-term gain in body mass, and look for physiological correlates to suggest an underlying mechanism. Retrospective analysis of 218 consecutive patients treated for sleep apnea at a community-based sleep center. A total of 152 patients met the criteria for study conclusion. After 1 month of CPAP treatment, 119 subjects (78%) gained mass, including 81% of men and 73% of women. As a group, subjects on CPAP gained 1.4±2.5 kg (mean±SD). The Epworth Sleepiness Scale was reduced after 1 month of CPAP therapy. There was no correlation between gain in body mass and measured parameters. A subgroup of 71 patients remained on therapy. They demonstrated a gain in mass at 4 weeks, which did not persist at 6 months. CPAP treatment of OSA is associated with gain in body mass at 1 month but not 6 months of therapy. The nature of this gain in mass remains unknown. We believe the gain is due to increased vascular volume, and might represent an early marker of physiological benefit of CPAP. This article includes a review of potential mechanisms for early increase in body mass with CPAP.