1. There was no significant incremental improvement in CRP levels at 24 weeks for the combined CPAP and weight loss counseling group versus either intervention alone.
2. There was a suggestion of improved serum triglycerides and insulin resistance at 24 weeks for the combined intervention versus CPAP alone.
Evidence Rating Level: 1 (Excellent)
Study Rundown: This randomized control study was designed to disentangle the complicated relationship between obstructive sleep apnea, obesity, and proatherosclerotic risk factors such as systemic inflammation, insulin resistance, and lipid levels among obese individuals with moderate-to-severe sleep apnea. Previous epidemiological studies have linked untreated obstructive sleep apnea and cardiovascular morbidity and mortality, but these relationships are likely confounded by the fact that sleep apnea is often diagnosed along with coincident cardiovascular risk factors such as metabolic and inflammatory disorders.
The study involved three intervention arms across 24 weeks (individualized weight loss program, CPAP (continuous positive airway pressure) alone, and combined/CPAP program) with a primary outcome of measured CRP (C-reactive protein) levels. At the end of the study period, there was no significant decrease in CRP levels (primary outcome) in the combined group versus the weight loss or CPAP groups alone. Secondary analyses showed an incremental benefit of weight loss therapy in terms of insulin resistance and serum triglycerides when compared to CPAP alone. These findings must be interpreted with caution, given concern for multiple testing and potential false positive results across the many endpoints. This suggests that for obese patients with moderate-to-severe sleep apnea who are prescribed CPAP, the addition of weight loss intervention may improve cardiovascular outcomes.
The greatest strength of study is the attempt to explore epidemiological relationships in the context of a randomized control study. Drawbacks include the relatively short follow-up period, the high attrition rate of 25% over the course of study follow-up, and the fact that cardiovascular and metabolic outcomes are measured in terms of biomarkers and not clinical end points.
Relevant Reading: Sleep-disordered breathing and mortality
Study author, Dr. Julio Chirinos, MD, PhD, talks to 2 Minute Medicine: Assistant Professor of Medicine at the Hospital of the University of Pennsylvania and the Veteran’s Administration Medical Center
“Among patients with obesity and moderate to severe OSA, obesity, rather than OSA, appears to be the primary cause of inflammation, insulin resistance and dyslipidemia. However, both obesity and OSA appear to be causally related to hypertension. In this population, weight loss, but not CPAP, can be expected to reduce the burden of inflammation, insulin resistance and dyslipidemia. However, CPAP, among patients who comply with therapy, can be expected to provide a significant incremental benefit on blood pressure. Weight loss should be the essential component of CV risk factor reduction in this population.”
In-Depth [randomized controlled trial]:This randomized control study compared the effects of CPAP, a weight loss program, and a combination of CPAP and a weight loss program on CRP levels (primary outcome) and secondary outcomes including lipid levels, insulin sensitivity (measured by frequently sampled IV glucose-tolerance test), and systemic blood pressure. Outcomes were assessed at 8 and 24 weeks after initiation. Study subjects were adults with a BMI greater than or equal to 30, moderate-to-severe obstructive sleep apnea, and CRP greater than 1.0 mg per liter.
Among the 146 participants, those assigned to weight loss program only and combined program had significant improvements in CRP levels, insulin resistance, and serum triglyceride levels; these changes were not seen for those in the CPAP alone group. In the primary outcome analysis, there was no significant incremental improvement in CRP levels for the combined program versus the CPAP or weight loss programs alone. Secondary analyses showed an incremental benefit of weight loss therapy in terms of insulin resistance and serum triglycerides when compared to CPAP alone (P=0.01 and P=0.046 for comparisons).
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