Sex Differences in the Association of Regional Fat Distribution with the Severity of Obstructive Sleep Apnea

OBSTRUCTIVE SLEEP APNEA (OSA) IS CHARACTERIZED BY REPETITIVE UPPER AIRWAY OBSTRUCTION DURING SLEEP.1 IT RESULTS FROM A COMBINATION of anatomic features that narrow the upper airway and the permissive effect of insufficient neuromuscular compensation during sleep.2 OSA is prevalent to a clinically significant degree in 2% of women and 4% of men,2 and obesity is the most common known risk factor.3–5 Excessive fat deposition may play a mechanistic role in OSA severity. Fat in the peripharyngeal area of the neck is thought to directly compress the upper airway.6 Chest-wall fat compresses the rib cage, reducing lung volume.7 Abdominal fat is thought to result in cranial displacement of the diaphragm, decreasing longitudinal tracheal traction on the upper airway and leading to increased propensity for upper airway collapse.8 Reduced prevalence and severity of OSA in women is likely to be a consequence of a more favorable pattern of distribution of excess fat. Specifically, women tend to distribute fat peripherally around the hips, buttocks, and thighs, whereas men tend to distribute excess fat more centrally on the abdomen and neck.9 As a result, although women have proportionally greater fat mass than men, they have less mechanical loading on their upper airway.9 However it is notable that most clinical studies examining the influence of obesity have been conducted in male populations10,11 or have included only small numbers of women12; therefore, the potentially important explanatory role of differences in pattern of obesity in determining differences in severity of OSA remains inadequately defined. Furthermore, traditional anthropometric measures used in studies of OSA include body mass index (BMI), waist and neck circumferences, neck-to-waist ratio (NWR), waist-to-hip ratio (WHR), and skin-fold anthropometry, which are of limited accuracy in determining fat distribution.5,13–15 More sophisticated methods are available to measure fat mass, such as magnetic resonance imaging (MRI) and computed tomography (CT), although they are unsuitable for studies requiring large populations. Dual energy absorptiometry (DXA) scanning is an accurate alternative measure of fat mass that is well suited for studies in clinical settings due to its relatively lower associated costs, training expertise, and radiation exposure.16 To date, it remains unknown whether DXA-measured regional fat can predict severity of OSA better than traditional anthropometric measures. In this study, we investigated whether traditional anthropometric measures, DXA-measured fat, or a combination of both best predicted OSA severity. We also investigated whether associations between OSA severity and regional fat distribution differed in men and women.