Important risk factors for OSA include obesity, male gender, and upper airway structural abnormalities (

Fig. 67-4). The majority of OSA patients are overweight, with more than 75% reported to be at least 20% over ideal body weight. A thick neck (circumference of more than 17 inches) has been correlated with sleep apnea risk in men.

The male predominance of OSA suggests that there may be important gender differences in upper airway anatomy and mechanics. Several studies have reported that many women with OSA are postmenopausal, suggesting that hormonal influences may be important. Premenopausal women with OSA are often morbidly obese. OSA can affect any age-group but appears to be most common in the middle-age years (30 to 70). In the Wisconsin Sleep Cohort Study, 4% of the men and 2% of the women in a middle-aged working population had symptomatic sleep apnea. Families with a high incidence of OSA have been reported, which may reflect genetic influences on body weight, upper airway structure, or respiratory drive. There is also a higher incidence of OSA in patients with hypothyroidism, acromegaly, and various congenital disorders (Down and Pierre Robin syndromes).