Background: Recent data has shown that CPAP increases weight in a dose-dependent manner compared to sham CPAP. However it not known whether this weight gain is associated with metabolic dysfunction in a dose-dependent manner.
Methods: Patient-level meta-analysis using the first arm of three randomised sham-controlled trials was performed to test whether patients gained weight in a dose-dependent manner. Metabolic markers (fasting glucose, insulin and insulin resistance [HOMA]) were also tested to indirectly determine whether weight changes might be due to increases in fat mass. Mixed model analysis of variance was used to quantify the effects of CPAP, dose (hours/night), their interaction and regression to the mean.
Results: 82 and 79 participants received CPAP and sham respectively. High use (>20 hours/week) was associated with greater weight gain across both treatments (difference 0.96 kg; 95%CI 0.0 to 1.9, p=0.04). CPAP increased weight compare to sham irrespective of dose however the difference did not reach significance (0.83kg; -0.08 to 1.7, p=0.07). High use of CPAP increased weight more than high use sham (1.4kg; 0.04 to 2.9, p=0.05) and more than low CPAP use (1.6kg; 0.4 to 2.8, p=0.01). There was no difference between high and low sham users (0.36kg; -1.0 to 1.7 NS). Neither treatment alone, CPAP dose alone nor the combined effect of both influenced glucose, insulin or insulin resistance.
Conclusion: High use CPAP increases weight compared to high use sham and low use CPAP without any subsequent changes in metabolic dysfunction. It is possible an increase in lean muscle mass rather than fat is the cause of the weight gain which may not necessarily have a detrimental effect on health.