Chapter 4 124 using a validated questionnaire for sleep disruptions. Sleep disruptions are difficult to estimate subjectively, and they could be affected by recall bias. Therefore, future studies could improve on this by using repeated sleep diaries to estimate day-to-day sleep disruptions, or more objective sleep measurements such as actigraphy or polysomnography. Perspective: reproductive context and sleep quality In the interpretation of this study, it must be noted that our results cannot be generalized to those with a previous or current psychiatric disorder. It is estimated that 32% of women and 26% of men in Denmark will have a lifetime psychiatric disorder (Kessing et al., 2023), meaning that the results in our study sample cannot be applied to a large proportion of the population. This is especially relevant to women, who have a higher risk of insomnia, depression and anxiety and are therefore a high-risk population. Therefore, more knowledge on the effects of OC use in those psychiatric patient groups is urgently necessary, since they are at the highest risk for insomnia. Conclusion In conclusion, we do not find sufficient evidence to confirm previously observed sex differences in sleep. We speculate if this reflects population differences in psychiatric history, since our group was selected towards robustness. Our results, however, do suggest that in healthy OC users, sleep quality is modestly poorer compared to NC women. Furthermore, we find that cortisol dynamics, in terms of the CAR, were associated with sleep quality in OC-using women and men, but not in NC women, which we speculate may be related to more rapidly fluctuating sex-hormone levels in NC women. Future studies should use longitudinal designs and clinical samples to further study the role of sex and hormonal contraceptive use on cortisol dynamics and sleep. Acknowledgements We wish to thank Peter Steen Jensen, Dorthe Givard and Birgit Tang for their help and administrative assistance in this project. The Cimbi database is supported by grants from the Lundbeck Foundation. This project was supported by the Amsterdam UMC foundation via a travel grant granted to M. Morssinkhof.
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