Chapter 1 12 1.2. Central theme of this thesis To better understand the impact of exogenous sex hormones and to elucidate the sex disparities in depression and insomnia, in thesis we aimed to study the effects of exogenous hormone use, specifically oral contraceptives and gender-affirming hormones, on depression and sleep. 2. Background: Sex hormones, depression and sleep 2.1. Sex hormones Estrogen, progesterone and testosterone are the body’s main sex hormones. Estrogen and progesterone are generally regarded as “female sex hormones” and testosterone as the “male sex hormone”, although all three sex hormones are present in both sexes. Generally, externally administered hormones forms are called exogenous sex hormones, to distinguish from hormones which are naturally produced by the body, which are called endogenous sex hormones. Endogenous sex hormones Endogenous hormone production is a well-orchestrated process that is coordinated by the Hypothalamic-Pituitary-Gonadal (HPG) axis. The hypothalamus produces gonadotropin-releasing hormone (GnRH), which triggers the anterior pituitary to produce luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in turn stimulate the gonads to regulate reproductive processes and produce sex hormones (Dwyer & Quinton, 2019). The female gonads produce progesterone and estrogen and the male gonads produce testosterone. The production of sex hormones is regulated by a negative feedback loop: in both males and females, estrogen regulates the release of LH, FSH and GnRH (Pitteloud et al., 2008a; Shaw et al., 2010), and testosterone also regulates GnRH release (Marques et al., 2000; Pitteloud et al., 2008b). This process is also illustrated in Figure 1.1. Estrogen and progesterone The HPG axis in female babies is shortly activated during prenatal development, and again in the postnatal period: this activation in the postnatal period is also called the neonatal minipuberty. The postnatal
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