CPAP Usage Causes Weight Gain
Frank J. Domino, MD
“In patients with obstructive sleep apnea, does CPAP cause weight gain or weight loss?” [Brager, LF, et al. Thorax 2014; 0:1-7)
An extensive review of the medical literature identified 25 randomized controlled trials covering over 3,000 patients. All of the included studies had a population that included mainly overweight and obese patients. Of significance is that the vast majority of excluded studies did not specifically identify outcomes with regards to body weight and BMI, and most studies that were included in this meta-analysis compared CPAP to no treatment for obstructive sleep apnea.
Results & Outcomes:
Meta-analysis demonstrated that CPAP promoted an increase in BMI as well as weight with a low risk for publication bias. This result came after adjusting for age, gender, baseline BMI, baseline weight, obstructive sleep apnea severity, CPAP compliance, use of sham CPAP, study duration, study design, study population, and recommendation for dietary change or physical activity as part of the study. The only predictor for an increase in BMI or an increase in weight was a high baseline weight.Conclusion:
Obstructive sleep apnea treated with Continuous Positive Airway Pressure promotes a statistically significant increase in BMI as well as weight.
It is long known that obesity increases the risk for sleep apnea. There is reasonable data demonstrating even a 10% increase in baseline weight corresponds to a > 30% increase in apnea-hypoapnea index (AHI) and a 6 fold increase in the risk of developing moderate to severe obstructive sleep apnea. It has also been well recognized that an appropriate treatment for obstructive sleep apnea is weight loss. A 10% weight loss predicts a 26% decrease in AHI score.
Obesity has long been considered a cause of obstructive sleep apnea through a variety of pathophysiologic mechanisms including upper airway narrowing due to fat deposition in the neck, reduced lung volume due to increased abdominal fat, a restrictive lung disease due to thoracic fat deposition, and instability of regular breathing associated with leptin resistance.
Once you have an increase in BMI and obesity your risk for obstructive sleep apnea seems to worsen by mechanisms including neurohormonal changes. These are known to control satiety and hunger, dietary habits, and a decreased motivation to exercise as well as a decreased ability to complete physical activity.
The logical assumption had been that treating obstructive sleep apnea with Continuous Positive Airway Pressure would result in improved physiologic parameters and help obese patients who wanted to lose weight be more able to do so. This study of randomized controlled trials demonstrates the opposite is true. While the degree of BMI and weight gain were not large over the course of the studies included (BMI increased by over 0.13 and weight increased about 0.5 kg) the finding of an increase in both BMI and weight is discouraging.
The authors of this meta-analysis recognized the studies included were well done, and had many strengths, but a number of limitations came to possibly influence its interpretation. First is that most of these randomized controlled trials were not designed to study the influence of CPAP on weight or BMI and that none of the studies did a detailed analysis of the participants dietary patterns or physical activities.
This raises though an opportunity for treatment going forward and a future study. It may be that the treatment of obstructive sleep apnea with CPAP should also require a component of counseling on weight loss and exercise. Potential future treatments could also include some required component with regard to close follow-up on not just the efficacy of the CPAP, but the efficacy of weight loss.
This study brings with it a call for future study regarding how best to treat obstructive sleep apnea. It should be incumbent upon all of us to become much more aggressive with our dietary counseling in those with obstructive sleep apnea. It may make the use of weight loss medications even more important in this population as not losing weight will certainly make their overall health considerably worse.
Frank J. Domino, MD, is Professor and Pre-Doctoral Education Director for the Department of Family Medicine and Community Health at the University of Massachusetts Medical School in Worcester, MA. Domino is Editor-in-Chief of the 5-Minute Clinical Consult series (Lippincott Williams & Wilkins).
Additionally, he is Co-Author and Editor of the Epocrates LAB database, and author and editor to the MedPearls smartphone app. He presents nationally for the American Academy of Family Medicine and serves as the Family Physician Representative to the Harvard Medical School’s Continuing Education Committee.