Cognitive factors increase the risk of shift work disorder through insomnia symptoms

The primary aims of the current study were to 1) investigate whether cognitive factors are associated with an increased risk of shift work disorder (SWD), and 2) whether symptoms of insomnia and/or excessive sleepiness mediate this association. Additionally, a third exploratory aim of the study was to examine whether these mediators of insomnia and excessive sleepiness vary in the relationship between cognitive factors and two phenotypes of SWD (i.e., SWD with high insomnia and low excessive sleepiness (SWD-I), and SWD with high excessive sleepiness with or without high insomnia (SWD-E)).

Shift workers (n = 126), predominantly working a schedule involving night shifts, completed a survey comprising measures of SWD risk, insomnia, excessive sleepiness, and cognitive factors, including pre-sleep cognitive and somatic arousal, dysfunctional beliefs about sleep, and sleep reactivity.

Logistic regressions found cognitive factors were not associated with SWD risk. Mediation analysis showed insomnia symptoms mediated the impact of pre-sleep somatic arousal, dysfunctional beliefs about sleep, and sleep reactivity on high SWD risk. Of those at high risk of SWD (37 %), 43 % and 34 % had the SWD-I and SWD-E phenotype, respectively. Insomnia symptoms mediated the relationship between all cognitive factors and SWD-I, but not SWD-E.

Although cognitive factors were not directly associated with SWD risk, insomnia severity, but not excessive sleepiness, was a significant cross-sectional mediator in the relationship between cognitive factors and risk of SWD. When exploring SWD phenotypes, cognitive factors were associated with a risk of having SWD when participants did not have excessive sleepiness (i.e., SWD-I). To expand on our findings, future research should investigate insomnia's role as a mediator in individuals diagnosed with SWD and to investigate the SWD phenotypes with larger samples.