Chapter 6 180 4. Discussion This study was the first to prospectively study effects of both masculinizing and feminizing sex hormones on sleep architecture in transgender persons. We found that 3 months of masculine sex hormone use resulted in decreased slow wave sleep duration, decreased REM sleep latency and increased REM sleep duration. However, 3 months of feminine sex hormone use showed no significant effects on sleep architecture. The results support our hypothesis that masculinizing hormones in persons assigned female at birth change the sleep architecture towards the opposite sex. However, feminizing hormones in persons assigned male at birth do not change sleep architecture, which does not support our hypothesis. In the transmasculine participants, the changes in REM sleep latency and duration and in SWS duration are notable. REM sleep latency shifts from a median of 87 to 68 minutes and the REM sleep duration shows an increase from a median of 111 minutes to 128 minutes. Considering a REM sleep duration of 21% to 30% in proportion of total sleep is considered healthy (Ohayon et al., 2017), these strong changes could be clinically relevant. The changes in SWS duration are small and not consistently significant after correction for repeated testing, with a 7-minute decrease in the raw SWS duration (corresponding to a Cohen’s d of 0.16) or 1.7% decrease in SWS percentage (corresponding to a Cohen’s d of 0.23), but very consistent across participants. This shows that the use of testosterone in persons assigned female at birth could affect SWS duration. Considering that the typically healthy range of slow wave sleep is from 16% to 20% (Ohayon et al., 2017), and participants showed a decrease from 21% to 19.5%, we would deem this change to be of interest for sleep science but of limited clinical meaning. Our results in the transfeminine participants mostly are in line with previous work conducted by (Kunzel et al., 2011). This study assessed the effects of 3 months of feminizing GAHT, specifically estrogen and cyproterone acetate, in seven transgender women. They found no significant changes in most sleep stages, but reported a specific increase in light (N1) sleep, from 33 minutes to 51 minutes. Our current study did not assess light sleep duration, and we could therefore not replicate the finding in N1 sleep.
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