Why Sleepiness Hits Some Postmenopausal Women With Sleep Apnea Harder

Excessive daytime sleepiness is one of the most disabling consequences of obstructive sleep apnea, a disorder in which the upper airway repeatedly collapses during sleep, cutting off airflow and fragmenting rest. Yet sleepiness does not strike everyone with the condition equally, and the factors that predict it in men or mixed-gender cohorts may not translate to women after menopause. A new retrospective cross-sectional study from a hospital-based sleep laboratory in Bangkok, published in Frontiers in Sleep, examined which overnight measurements best discriminate sleepy from non-sleepy postmenopausal women with obstructive sleep apnea, and the answer centers on respiratory burden and the depth of nocturnal oxygen desaturation rather than on sleep fragmentation alone.

The research team, led by Thanida Manitchotpisit and Mart Maiprasert of Dhurakij Pundit University together with colleagues at Samitivej Thonburi Hospital and Chulalongkorn University, analyzed records from 216 postmenopausal women whose obstructive sleep apnea had been confirmed by Level 1 polysomnography, the gold-standard in-laboratory sleep test. All participants completed the validated Thai version of the Epworth Sleepiness Scale, an eight-item questionnaire rating the likelihood of dozing in everyday situations, on the same day as their sleep study and before any treatment began. A score of 10 or above classified a woman as having excessive daytime sleepiness, which applied to 110 participants, while the remaining 106 scored below the threshold.

The polysomnographic recordings themselves were extensive, incorporating electroencephalography from frontal, central, and occipital electrodes, electrooculography, submental and anterior tibialis electromyography, electrocardiography, airflow measured by oronasal thermocouple and nasal pressure transducer, thoracoabdominal respiratory effort, snoring sensors, body position, and pulse oximetry. Sleep staging and respiratory event scoring followed the American Academy of Sleep Medicine 2012 manual, with apneas defined as airflow reductions of at least 90 percent lasting ten seconds or more, and hypopneas as decreases of at least 30 percent accompanied by either a 3 percent oxygen desaturation or an EEG arousal. Certified sleep technologists scored every recording under board-certified sleep physicians.

A central metric in the analysis was the respiratory disturbance index, calculated as the total number of obstructive apneas, hypopneas, and respiratory effort-related arousals per hour of sleep. Unlike the more familiar apnea-hypopnea index, the respiratory disturbance index captures subtle breathing disturbances that fragment sleep without meeting full apnea or hypopnea criteria. The researchers also computed position-specific and sleep-stage-specific versions, separating supine from non-supine values and rapid eye movement from non-rapid eye movement values, alongside mean and minimum oxygen saturation and the percentage of sleep time spent below 90 percent saturation.

The results revealed a striking pattern. Women with excessive daytime sleepiness were younger on average, at 60.3 versus 62.6 years, and carried more central adiposity, with higher body mass index and larger neck circumference. More tellingly, their overnight respiratory burden was substantially heavier: overall respiratory disturbance index averaged 40.1 events per hour in the sleepy group versus 28.3 in the non-sleepy group, with rapid eye movement values reaching 48.8 versus 34.5. Their minimum oxygen saturation dipped lower, averaging 79.0 percent versus 83.2 percent, and they spent a greater proportion of sleep time below the 90 percent saturation threshold.

When the researchers adjusted for age, body mass index, and neck circumference in multivariable logistic regression, five parameters remained independently associated with sleepiness: higher overall, supine, rapid eye movement, and non-rapid eye movement respiratory disturbance indices each raised the odds, while higher minimum oxygen saturation lowered them. Notably, the arousal index and sleep efficiency, measures of sleep fragmentation that previous studies in predominantly male cohorts had sometimes linked to sleepiness, showed no significant association in this population. The depth of oxygen desaturation, rather than the frequency of cortical arousals, appeared to track subjective sleepiness most closely.

To build a practical discrimination model, the team retained four predictors based on univariable performance and overall model discrimination: overall respiratory disturbance index, rapid eye movement respiratory disturbance index, mean oxygen saturation, and minimum oxygen saturation. This four-variable model yielded an area under the receiver operating characteristic curve of 0.693, indicating moderate discriminative ability, with a positive predictive value of 63.89 percent and a negative predictive value of 62.04 percent. Multicollinearity checks using the variance inflation factor confirmed the predictors were statistically compatible, with a mean value of 2.54.

The prevalence of excessive daytime sleepiness in the cohort reached 50.9 percent, comparable to the 44.6 percent reported among women in the large Swedish SESAR registry and within the 40.5 to 58 percent range observed in newly diagnosed obstructive sleep apnea populations. The finding that younger postmenopausal women were more susceptible to sleepiness runs counter to some prior evidence linking aging with increased apnea burden, but the authors suggest that beyond midlife, age-related reductions in sleep need and adaptation to chronic sleep disruption may attenuate subjective sleepiness despite persistent breathing disturbances.

The mechanistic story behind these associations weaves together hormones, anatomy, and sleep physiology. Declining estrogen and progesterone after menopause remove protective effects on upper airway tone and ventilatory drive: progesterone normally stimulates respiratory effort and upper airway dilator muscle activity, while estrogen supports sleep stability and reduces arousal susceptibility. Simultaneously, menopause promotes central adiposity and fat deposition around the upper airway and thoracic cavity, increasing pharyngeal collapsibility. Because respiratory events in women cluster during rapid eye movement sleep, a stage of generalized muscle atonia and altered ventilatory control, events in that stage tend to be longer and more severe, producing deeper desaturations.

Recurrent intermittent hypoxia, particularly when oxygen saturation nadirs plunge profoundly, triggers oxidative stress, neuroinflammation, and dysregulation of neurotransmitter systems that impair wake-promoting neural circuits. Repeated desaturations also activate the sympathetic nervous system and disrupt slow-wave and rapid eye movement sleep, stages essential for physical restoration and cognitive function. The authors caution that polysomnographic variables alone cannot fully explain individual variability in sleepiness, noting that women more often report fatigue or non-restorative sleep rather than classical sleepiness, and that coexisting insomnia may confound Epworth scores. Still, the findings support using hypoxemia-focused metrics such as nadir oxygen saturation alongside event frequency when assessing the daytime consequences of obstructive sleep apnea in postmenopausal women, and they may inform risk communication, earlier continuous positive airway pressure initiation, and safety counseling regarding driving and other activities requiring sustained alertness.

Subject of Research: Polysomnographic determinants of excessive daytime sleepiness in postmenopausal women with obstructive sleep apnea

Article Title: Polysomnographic characteristics of excessive daytime sleepiness in postmenopausal women with obstructive sleep apnea

Article References: Manitchotpisit, T., Sugkraroek, P., Segsarnviriya, C., Chirakalwasan, N., & Maiprasert, M. (2026). Polysomnographic characteristics of excessive daytime sleepiness in postmenopausal women with obstructive sleep apnea. Frontiers in Sleep, 5, Article 1853970. https://doi.org/10.3389/frsle.2026.1853970

Image Credits: AI Generated

DOI: 10.3389/frsle.2026.1853970

Keywords: obstructive sleep apnea, excessive daytime sleepiness, polysomnography, postmenopausal women, respiratory disturbance index, nocturnal hypoxemia, Epworth Sleepiness Scale, REM sleep, menopause, sleep medicine, Polysomnographic, characteristics