Common risk factors contributing OSAS asthma: OSAS and asthma share some common risk factors. Fifty percent of the obese in Caucasian populations have OSAS, and among those with OSAS, 40% are obese. However, in a community study of sleep-disordered breathing in middle-aged Chinese men in Hong Kong, the average body mass index (BMI) of habitual snorer was 25.1 kg/m2 and that of OSAS was 27kg/m2, making the contribution of obesity in OSAS less as important as in the western counterpart. Apart from obesity, the prevalence of GER is increased in patients with OSAS. It has been suggested that obesity contributes to the same risk factors for OSAS and GER. However, OSAS patients exhibit significantly more GER than do members of the average population even when one controls for alcohol intake and BMI. GER occurring during sleep is a well-known trigger for nocturnal asthma and can provoke asthma symptoms through vagal reflexes induced by exposure of the esophagus to acid. OSAS-induced acid reflux may play a causative role in triggering asthma symptoms. Another possible etiology for the high prevalence of OSAS symptoms in asthmatic patients is the increased incidence of nasal obstruction in asthmatic patients. The nose is preferred breathing route during sleep, and nasal obstruction contributes to sleep disordered breathing in predisposed individuals. Rhinitis and chronic sinusitis are common conditions that may cause nasal congestion and consequently contribute to upper airway obstruction in OSAS.