Chapter 8 232 study used actigraphy (Lee et al., 2000), five studies used validated sleep questionnaires (Baker et al., 2012; de Zambotti et al., 2015; Freeman et al., 2004; Hollander et al., 2001; Kische et al., 2016) and six studies used sleep items from other questionnaires (Ben Dor et al., 2013; Gingnell et al., 2013; Kravitz et al., 2005; Lee et al., 2000; Li et al., 2015; Toffol et al., 2019). A number of studies combined different methods of sleep assessment (Baker et al., 2012; de Zambotti et al., 2015; Kische et al., 2016; Lee et al., 2000). Because of the heterogeneity of assessment methods for sleep and depressive symptoms, it was not possible to determine mean risk ratios or effect sizes of sex hormones on depression or sleep across the studies. 3.5. Demographics of study participants Only one study (Kische et al., 2016) included both male and female participants. Studies varied in age range of participants; part of the studies assessed participants at the end of the reproductive life phase towards menopause (35-55 years old), others assessed only younger women (18-27) or chose a broader age range. Kische et al. (2016) was included despite their age range, which exceeded our set age range (18 to 45). This study was of additional value for our review as this was the only study that included men, and the authors corrected for age in all the reported results. The ages and sample sizes of all included studies are also displayed in Figure 8.2. 3.6. Established link between sleep and depression Most study outcomes on the association between sleep and depression are consistent with previous research. They indicate an association between poor subjective sleep (daily diary, question item “Did you have trouble sleeping”) and depressive mood (Kravitz et al., 2005). Additionally, when subjective sleep quality worsens (measured using St. Mary’s Sleep Questionnaire) depressive symptoms increase (Hollander et al., 2001) and the risk of MDD diagnosis rises (Freeman et al., 2004; Hollander et al., 2001). In studies using PSG measurements, depressed participants were found to have a longer sleep onset latency, spend more time in shallow sleep and show altered ratios of delta sleep compared to controls (Antonijevic et al., 2003). Only Kische et al. (2016) found no significant differences in sleep PSG or sleep quality after grouping based on whether participants had experienced depression in the past.
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