General discussion 257 General discussion The aim of this thesis was to examine whether the use of exogenous sex hormones could affect depression and sleep. In numerous empirical studies, we investigated the effects of oral contraceptives (OCs) and gender-affirming hormone therapy (GAHT) on depressive symptoms, sleep quality, insomnia, sleep architecture and sleep timing, and in a systematic review, we summarized studies on sex hormones, depression and sleep. In this chapter, the findings of this thesis are summarized, possible underlying mechanisms are discussed, strengths and limitations of the different study setups are evaluated and directions for future research on sex hormones, depression and sleep are addressed. 1. Summary of main findings 1.1. Sex hormones and depression We examined the association between sex hormones and depression in Chapter 2 and Chapter 3. In Chapter 3, we used data from a longitudinal cohort study to retrospectively assess differences in depressive symptoms and depression diagnoses between OC users and naturally cycling women. In the overall group, we found no significant differences in depression prevalence or symptom severity between OC users and naturally cycling women. However, estimation of the within- and between-person estimates showed opposing results. Between-person estimates indicated that participants who reported using OCs more often showed a lower prevalence of depression and lower depression symptom severity. Within-person estimates in the subgroup of participants who contributed measurements during both OC use and natural cycles, however, showed that presence and severity of depression was higher during OC use compared to non-use. In Chapter 3, we studied depressive symptom profiles before GAHT use, and we examined changes in depressive symptom profiles after 3 and 12 Research question 1: Are OC use and GAHT use associated with changes in depressive symptoms?
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