Unexpected BMI Changes Seen After CPAP Therapy
SEATTLE, WA—An increase in body mass index (BMI) was observed following initiation of continuous positive airway pressure (CPAP) therapy, so implementation of nutritional and exercise interventions is recommended, according to data reported at SLEEP 2015 by Erin E. Reese, MPH, Beth Israel Deaconess Medical Center, Boston, MA.
Reese and colleagues analyzed data from the Best Apnea Interventions in Research (BestAIR) and the Heart Biomarker Evaluation in Apnea Treatment (HeartBEAT) trials (n=169 and 212, respectively) in participants with established or significant risk factors for cardiovascular disease and moderate to severe obstructive sleep apnea (OSA). Subjects had been randomized to receive either active CPAP or a control treatment (sham CPAP or healthy lifestyle education) over durations from three to 12 months.
BMI was measured at baseline, midpoint (when applicable), and final study visit; change in BMI was analyzed by trial, using linear mixed effects models. Baseline characteristics were similar for the CPAP and control groups.
In both trials, mean BMI statistically significantly increased from baseline to follow-up in the CPAP group, but remained nearly unchanged in the control group at three and 12 months. The difference in treatment effect by arm (CPAP vs. controls) on change in BMI from baseline was 0.40kg/m2 (95% CI: 0.15, 0.65) for HeartBEAT at three-month follow-up and 0.41kg/m2 (95% CI: -0.05, 0.86) for BestAIR (mean of six- to 12-month follow-ups), suggesting that BMI increases over time with CPAP treatment.
Since treatment for OSA with CPAP can improve alertness, mood, and vigor, it has been assumed that the intervention positively influences physical activity and caloric expenditure, thereby reducing body weight. These findings, however, do not bear out that assumption. It appears as though CPAP use may reduce energy expenditure during sleep, due to reduced work of breathing or unanticipated changes in appetitive behaviors.
“Increased BMI may alter positive airway pressure requirements, suggesting a role for ongoing monitoring of body weight and positive airway pressure needs,” Dr. Reese concluded.