Overweight and Obesity
Obesity is the clearest risk factor for obstructive sleep apnea. However, patterns of fat distribution may affect men and women differently. In 151 patients undergoing sleep studies, neck and waist circumference, and waist-to-hip ratio were evaluated. In men, neck circumference and waist-to-hip ratio were significantly associated with the apnea-hypopnea index, a measure of sleep apnea severity. In women, only waist-to-hip ratio was significantly associated with apnea-hypopnea index (Lim 2014; Ayas 2014).
Smoking increases the risk of obstructive sleep apnea, and of developing obstructive sleep apnea at an earlier age than people who never smoked. Cigarette smoking increases upper airway resistance as a result of inflammation, swelling and increased mucus secretion, which may explain this association (Boussoffara 2013; Hizli 2013; Quan 2014; Lin 2012).
Allergies and Asthma
In a study in over 1900 individuals, the combination of asthma and allergic rhinitis was associated with 1.44-fold increased odds of obstructive sleep apnea compared to those with just asthma. When allergic rhinitis duration and severity were taken into account, the odds rose to 1.99-fold. The authors concluded that allergic rhinitis, independent of obesity and other risk factors, contributes to the risk of sleep apnea (Braido 2014).
Gender and Ethnicity
Men are at twice the risk of obstructive sleep apnea compared with women (Sutherland 2012; Valipour 2012). African American men under age 39, and between 50 and 59, have more severe sleep apnea compared with white men of the same age (Pranathiageswaran 2013; Sutherland 2012). In Asians, the association of obstructive sleep apnea with obesity is not as strong as in other ethnicities (Chirakalwasan 2013).
The risk of sleep apnea increases with age. This may be due to factors such as diminished efficiency of muscles and soft tissues in the upper airway or reduced sleep quality (Jordan 2014).
Declining Hormone Levels (in Women)
The risk of sleep apnea increases significantly after menopause, and some evidence suggests female reproductive hormones play a protective role against obstructive sleep apnea (Dursunoglu 2009; Tamanna 2013; Keefe 1999; Dancey 2001; Tasali 2008). Indeed, a preliminary study showed that estradiol plus progestin therapy or estradiol alone reduced the severity of sleep apnea in five postmenopausal women (Keefe 1999).
Family History and Narrow Airways
Obstructive sleep apnea may have a hereditary component, perhaps because its risk factors also run in families (Hayes 2014; Thompson 2012). These include anatomical features of the airway and obesity (Redline 1995; Jordan 2014).