Daytime sleepiness is a common symptom of obstructive sleep apnea (OSA) and is more common in men, but the underlying mechanism remains unclear. The aim of this study was to assess whether or not sex differences in daytime sleepiness persisted after controlling for age and OSA severity and to explore the factors contributing to daytime sleepiness in patients with OSA.

A total of 104 pairs of patients with OSA, matched by age and apnea-hypopnea index (AHI), were enrolled in this retrospective study. Demographic data were collected; daytime sleepiness was measured by the Epworth Sleepiness Scale (ESS); and polysomnography (PSG) was performed on each participant. These measurements were compared between sexes, and the factors affecting daytime sleepiness were explored with correlation and multivariate linear regression analyses.

Men had significantly higher ESS scores (p = 0.021) than women. Regarding demographics, BMI, neck/height ratio, and proportion of habitual smoking and alcohol intake were significantly higher in men. Regarding PSG findings, men had more rapid eye movement sleep, a longer mean apnea-hypopnea duration, and a longer mean apnea duration (MAD). Regression analysis showed that two sex-associated variables, habitual smoking (β = 0.189, p = 0.006) and MAD (β = 0.154, p = 0.024), had the strongest association with ESS scores. Further analysis revealed that MAD was significantly influenced by apnea index (β = 0.306, p < 0.001) and sex (β = − 0.193, p = 0.003).

The sex difference in daytime sleepiness persists in patients with OSA, even after matching AHI and age. The difference is mediated by sex-specific smoking habits and sex differences in apnea duration.