Chapter 9 278 blunting”, and studies on GAHT indicate that feminizing GAHT is associated with an increase in emotion intensity (Slabbekoorn et al., 2001; Wassersug et al., 2007), by some described as an “emotional rollercoaster”. Therefore, future studies on sex hormones and mood should also account for changes in day-to-day emotions and emotion variability. These should be studied using daily ratings, for example using the Daily Record of Severity of Problems (DRSP; Endicott et al., 2006), which is commonly used in research on PMDD and OC use, or through assessment with Ecological Momentary Assessment (EMA), in which items could also be adapted to best reflect the most relevant emotions. Recommendations for studies of sex hormones and sleep The findings in this thesis show that the use of exogenous sex hormones could contribute to changes in sleep architecture and chronotype in a sexspecific manner, with GAHT use resulting in changes in sleep which partially align with the sex differences in the cisgender population. Future studies should elaborate on these findings in two domains: firstly, in the domain of sleep architecture and sex hormone exposure, and secondly, in the domain of chronotype and hormone therapy. Firstly, in Chapter 6, we hypothesized that the sensitivity to the effect of sex hormones on sleep architecture could be dependent on previous sex hormone exposure, based on the possible organizational effects of sex hormones (Bakker & Brock, 2010; McCarthy, 2010). The effects of chronic sex hormone exposure in adolescence on sex-hormone sensitivity in adulthood could be studied further by examining sleep architecture in females who used hormonal contraceptives during adolescence compared to females who did not. Based on the hypothesis that sex hormone exposure during adolescence can change sensitivity to sex hormones, those who used OCs during adolescence could experience stronger or weaker effects of the menstrual cycle, OCs, pregnancy and menopause on sleep in adulthood. Secondly, in Chapter 7, we showed that chronotype changed after GAHT use, meaning exogenous sex hormones could affect chronotype. This finding is relevant to the field of sex differences, but also for those who use exogenous sex hormone therapies, including menopausal hormone therapy, hormone therapy for oncological treatments, or hormones for fertility treatments, who might experience shifts in chronotype. To improve our
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