The number of people affected with obstructive sleep apnea (OSA)—an underdiagnosed clinical condition characterized by recurrent episodes of upper airway obstruction—is increasing worldwide, and as the obesity epidemic continues, the number can be expected to keep growing. Obesity predisposes individuals to OSA, but whether OSA is merely a secondary occurrence with metabolic syndrome or a factor that exacerbates the cardiometabolic risk attributed to obesity and metabolic syndrome remains a challenging question.

In a review of recent literature, Luciano F. Drager, MD, PhD, from the Heart Institute of Sao Paulo Medical School, Brazil, and colleagues examined the associations among OSA and obesity and metabolic syndrome and attempted to determine why OSA remains unrecognized in a vast majority of these patients despite such an overwhelming association.

The literature cites several mechanisms for the relationships among OSA and metabolic syndrome and obesity, and several clinical and epidemiological studies report an independent association between OSA and CV events, suggesting that OSA may lead to cardiometabolic dysregulation independently of obesity and metabolic syndrome.

However, the vast majority of the clinical studies that evaluated the impact of obesity and the metabolic syndrome on CV burden failed to consider OSA as a potential confounding factor. "This may reflect a low awareness of OSA in the cardiovascular field associated with the perception that OSA is merely an epiphenomenon of obesity," the review authors noted.

Drager et al. also discuss recent studies that have explored the impact of OSA on metabolic syndrome and its components through a reverse design. For instance, one study demonstrated that continuous positive airway pressure therapy reduced several components of the metabolic syndrome (including BP, triglycerides, and glucose levels); treating OSA, then, has the potential to reduce the CV burden associated with metabolic syndrome.

Despite the evidence in current literature supporting the role of OSA as an emerging risk factor for modulating the cardiometabolic consequences of obesity, the condition remains underdiagnosed. To counter this lack of awareness, Dr. Drager and colleagues suggest first implementing more screening for OSA in obese patients and those with metabolic syndrome. More comprehensive genetic studies would also shed some light on the reasons why a portion of obese patients do not develop OSA and other gaps in knowledge. "There is a clear demand for additional research, both at the basic science and clinical levels, for understanding the mechanisms by which OSA and its components exacerbate metabolic dysfunction and vascular impairment in obesity and metabolic syndrome," the authors concluded, but larger randomized studies are needed.

Drager LF, Togeiro SM, Polotsky VY, Lorenzi-Filho G. J Am Coll Cardiol. 2013 May 24. [Epub ahead of print]

Keywords: Metabolic Syndrome, Epidemiologic Studies, Schools, Medical, Risk Factors, Obesity, Awareness, Sleep Apnea, Obstructive

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