A previous epidemiological study reported that males have higher prevalence rates of a diagnosis and severity of obstructive sleep apnea syndrome (OSAS) than females, with a ratio of 2:1 to 3:1 [1]. Gender differences in craniofacial shape and fat deposition seem to be the most important issues between males and females [2,3]. Obesity is a well-known risk factor for the development of OSAS in both genders [4–7]. Moreover, Yukawa et al. reported that Japanese females had lower apnea–hypopnea index (AHI) values than Japanese males after adjusting for body mass index (BMI) and that male patients with OSAS had a higher continuous positive airway pressure (CPAP) compared to female patients with OSAS [8].
