The impact of sex and menstrual phase on complex cognitive performance, sleepiness and mood during a simulated night-shift

In the luteal stage of the menstrual cycle, core body temperature increases during the night circadian cycle which results in better performance on simple cognitive tasks. In the follicular stage, increased performance is found on sexually dimorphic tasks favouring men. This effect has not been tested in the context of misaligned sleep cycle. The aim of this study was to investigate the impact of sex and menstrual phase on complex cognitive performance, sleepiness and mood during a simulated night-shift. The participants, 22 men, 9 luteal stage women and 5 follicular stage women, completed a Serial Addition-Subtraction Task (SAS), Conjunction Search Task and Spatial Configuration Task at regular intervals during a simulated night shift in a sleep laboratory. Subjective mood and sleepiness were also assessed during the simulated night shift using a Profile of Mood States and the Karolinska Sleepiness Scale, respectively. There was no difference between groups in the percentage of correct responses on the SAS task and the spatial configuration task, or self-reported mood and sleepiness. There was a difference between groups in the percentage of correct responses on the conjunction search task with men and luteal stage women performing better than follicular stage women. This study shows that the vulnerability to sleep restriction due to menstrual cycle is not completely evidenced in the context of complex cognitive tasks over a single night of simulated shift work. Nevertheless, a more robust method of menstrual stage classification than self-report, as well as identifying participants’ menstrual cycle substages (early/late, follicular/luteal stages) is recommended in future studies.