We thank Dr. Kawada for his interest in our article [1]. He raised some important issues. We could not specify the effect of cardiovascular disease (CVD) on sex difference in the prevalence of sleep and psychological disturbances.

There has been accumulating evidence regarding sex differences of sleep and psychological disturbances in the general population. For instance, in a nationwide, cross-sectional study on sleep from the Korean general population, the prevalence of insomnia symptoms was higher in women than in men [2]. The meta-analysis confirmed a female predisposition of insomnia (risk ratio 1.41, 95% CI 1.28–1.55), and the use of various criteria did not influence the female predisposition to insomnia [3]. These findings are consistent with our research in patients with various cardiovascular diseases. The female predisposition of insomnia may be universal regardless of CVD.

Elucidating the mechanism of higher prevalence of insomnia in females was beyond the scope of our study. Despite adjustments using various factors (e.g., age, obesity, hypertension) in our study, unmeasured variables (e.g., iron deficiency anemia, restless leg syndrome) or other unknown variables related to hormonal and nutritional factors may have influenced the high prevalence of insomnia in females.

There are inconsistent findings regarding sex-specific differences in the relationship between sleep-disordered breathing (SDB) and CVD. Among the total of 1927 men and 2495 women free of coronary heart disease and heart failure at the time of baseline polysomnography, obstructive-type SDB predicted incident heart failure in men but not in women (adjusted hazard ratio 1.13, 95% confidence interval 1.02–1.26 per 10-unit increase in apnea hypopnea index) [4]. On the other hand, among 752 men and 893 women free of CVD participating in both the Atherosclerosis Risk in the Communities and the Sleep Heart Health Studies, obstructive-type SDB was independently associated with high-sensitivity troponin T as well as incident heart failure or death among women but not in men. Notably, among surviving participants without an incident CVD event, obstructive-type SDB was associated with higher left ventricle mass index only among women [5]. These inconsistent results may be due to differences in demographic characteristics in each cohort. Whether or not the effect of SDB on cardiovascular outcome may be modified by sex is still not well understood, and future studies will be warranted to examine this question.