Predictors of obstructive sleep apnea: special considerations for females.

To the Editor: I read with interest the article by Ibrahim et al exploring the predictors of obstructive sleep apnea (OSA) in snorers.1 The authors reported no age difference between females with and without OSA. For females, including age without considering the menopausal status can be misleading. In females, the menopausal status is one of the most important risk factors and predictors of OSA and its assessment is an essential part of any study looking into OSA in females. Young et al assessed the association between the menopausal status and sleep-disordered breathing (SDB) in women.2 After adjusting for potential confounders like age, body mass index and smoking, the authors calculated the odds ratio (95% CI) for an apnea/hypopnea index (AHI) of more than five per hour of sleep to be 1.2 (0.7–2.02) in perimenopausal and 2.6 (1.4–4.8) in postmenopausal women.2 After menopause, the prevalence of OSA in women approaches that in men and reaches its peak in the fifth and sixth decades.2,3 In general, the prevalence of OSA peaks at around 55 years in men and at around 65 years in women.4 This can be related to postmenopausal status as the risk of SDB was shown to be at least 2.5 times higher in post-than in premenopausal women, 2 and it approximates that of men at the time of menopause.5 Female hormones (especially progesterone) may play a role in increasing upper airway muscle activity during wakefulness and non-rapid eye movement sleep.6 Furthermore, there are important gender differences in central ventilatory control. Women have a lower apnea threshold, compared to men and they are less likely to exhibit apneas during non-rapid eye movement sleep despite inspiratory flow limitation.7,8 It is possible that the above protective mechanisms disappear after menopause. Another point to remember when evaluating females for SDB is the fact that a good proportion of females with OSA present with insomnia rather than excessive daytime sleepiness. Shepertycky et al in a study of 260 patients found that 1 in 5 women with OSA had a presenting complaint of insomnia compared to 1 in 20 in men.9 We found similar findings in Saudi females with OSA (under review).

We agree with the listed predictors of OSA in Ibrahim’s study. However, it is important for clinicians to realize that SDB in females is slightly different from that in males. Menopausal status is an important risk factor for OSA. Additionally, it is important to recognize that insomnia could be the presenting symptom of OSA in females. Focusing on daytime sleepiness in this group of patients may result in under-recognition of this serious disorder.