Cortisol dynamics and sleep quality: the role of sex and oral contraceptive use 121 have not found any difference in sleep quality between users and non-users of OCs (Hachul et al., 2013, 2020). In our study and numerous previous studies, however, it is important to note that study findings could be affected by healthy user bias. Since side effects are a common reason to stop using OC (Hall et al., 2014), OC users who experienced side effect could be more predisposed to stopping OCs, meaning this group could be underrepresented in our study. Based on the estimated proportions of sleep disruptions, showing strongly overlapping probabilities of sleep disruptions in OC users and NC women, we do not find the higher rate of disrupted sleep in OC users which was previously found in Morssinkhof et al. (2021). This could be due to differences in study setup: the current study was limited in power, because of the lower sample size (n=118 compared to n=1205) and the ordinal nature of the sleep disruption outcome, as well as due to due to the differences in the scales used (the PSQI vs. the WHI-IRS). Furthermore, it could also be due to differences in sample selection, since the previous study selected a sample with a high prevalence of lifetime depression diagnoses and the current sample selected only participants without lifetime psychiatric diagnoses. The analyses comparing men to NC women find no significant sex differences, which is notable in the broader context of sex differences in sleep. Epidemiological studies in community samples find a higher prevalence of insomnia and poor sleep in women compared to men (Zhang & Wing, 2006). One possible explanation for this discrepancy could relate to the screening method for participants in our sample. In previous studies, rates of insomnia and poor sleep have been examined without taking into account psychiatric history, whereas in the current study, we screened participants for psychiatric disorders and excluded those with previous or current disorders. Earlier studies have posed that in the general population, the higher prevalence of insomnia in women is associated with a higher prevalence of anxiety and depression (Hale et al., 2009). This would implicate that when constraining study samples to women without previous or current psychiatric disorders, the magnitude of sex differences in sleep quality and insomnia is lower. This could explain the possible lack of sex difference in our current sample, although the topic needs further study.
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