The Hefty Price of Obstructive Sleep Apnea

Reference as: Budhiraja R. The hefty price of sleep apnea. Southwest J Pulm Crit Care 2011;3:169-71. (Click here for a PDF version)

Obesity is approaching an epidemic level in the United States. The association between obesity and obstructive sleep apnea (OSA) is quite strong and likely causal. Approximately half of obese individuals have OSA and the risk of OSA increases with increasing BMI. Conversely, majority of individuals with OSA are obese. However, whether this relationship is bidirectional and OSA can, in turn, contribute to obesity is unclear.

The study by Brown and colleagues in the Journal attempts to answer this question ¹. The authors analyzed prospectively obtained data from a large community-based cohort and found that the participants with more severe sleep disordered breathing at baseline demonstrated a modest increase in body mass index (BMI) over a 5 year follow up period.

What can these intriguing results be attributed to? Pathophysiology of obesity is a multifactorial and complex process and may include dietary, lifestyle and genetic components.  As the authors hypothesize, an alteration in leptin-ghrelin levels in OSA may contribute to obesity. However, independent effect of sleep apnea on these metabolic hormones is still not clear. Studies in OSA, in contrast to those with sleep deprivation, actually suggest increased daytime leptin levels, primarily explained by obesity ². Similarly, contradictory data exist regarding ghrelin levels in OSA. While some studies demonstrate an increase in ghrelin levels ^{3, 4}, others do not ^{5, 6}. A decrease in energy expenditure is a plausible mechanism whereby OSA may lead to further weight gain. It is easily fathomable that disturbed sleep in obese people may contribute to daytime fatigue and lethargy and promote a more sedentary lifestyle.  However, convincing data from large studies confirming such an association is again lacking. Finally, an altered feeding behavior with a preference for a weight-gain promoting diet may be seen in sleep disordered breathing and contribute to obesity ⁷.

The strengths of this study include a large sample size derived from community-based cohorts, prospective collection of data and objective documentation of sleep abnormalities. However, the readers should bear in mind that the adjusted increase in BMI was fairly modest- in order of 0.21 kg/m² in those with mild OSA and 0.51 kg/m² in moderate to severe OSA. Furthermore, the statistical models used in the study accounted for only 7% of the total variance, suggesting that the factors not included in analysis likely played a prominent role in the weight gain.

Nevertheless, this study adds to emerging literature suggesting SDB as a risk factor for weight gain ^{8, 9}. Ideally, these data suggest need for well conducted prospective studies looking at physical activity, diet and change in BMI in patients with SDB. However, in view of the now well recognized adverse effects of severe sleep apnea, it will not be feasible to conduct long-term studies in these patients without offering treatment.  The other line of evidence that would support the hypothesis that sleep apnea predisposes to weight gain, would be weight loss with adequate therapy. Indeed some studies have assessed this, but with variable results ^10-12. Some of the factors underlying such variability in results may include differences in dietary habits, physical exercise, age of the participants, sleep duration, use of medications and presence of additional comorbidities ¹³. Future studies, apart from controlling for these variables, should also consider evaluating changes in central obesity instead of, or in addition to BMI, as the former may be a better marker of adverse cardiovascular outcomes than BMI ¹⁴.

Finally, obesity is a risk factor for an array of cardiovascular and metabolic adverse outcomes. This study provides further rationale to add abnormal sleep to unhealthy diet and lack of exercise as crucial factors that need to be modified to curb the obesity epidemic. Further longitudinal and interventional studies are required to help confirm these observations and assess the impact of better sleep on health outcomes.

Rohit Budhiraja, M.D.^{1, 2, 3}

Associate Editor

Southwest Journal of Pulmonary and Critical Care 

¹ Department of Medicine, Southern Arizona Veterans Affairs Health Care System (SAVAHCS) , Tucson, AZ

² Arizona Respiratory Center, The University of Arizona, Tucson, AZ

³ Department of Medicine, University of Arizona College of Medicine, Tucson, AZ

Corresponding Author:

Rohit Budhiraja, MD

Southern Arizona VA HealthCare System,

3601 S 6^th Ave,

Tucson, Arizona 85723

rohit.budhiraja@va.gov

Phone: 520-331-2007

Fax: 520-629-4641

References

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