Circadian Type Determines Working Ability: Poorer Working Ability in Evening-Types is Mediated by Insufficient Sleep in a Large Population-Based Sample of Working-Age Adults

BACKGROUND: Circadian phenotype has a crucial role in determining wellbeing and health prospective. Evening-types have higher risk for sleep and mental health problems, which is also reflected in work wellbeing. However, there are no population-based studies examining the association of working ability and circadian typology at different working-age-groups. Also, the role of predisposing factors, ie, sleep-related differences between circadian types, has not been studied in relation to working ability among circadian types in a population-based sample. METHODS: In this population-based sample of 13,114 working-age Finnish adults from 18 to 64 years of age, we examined the associations between circadian type, exhaustion and working ability and the roles of sleep-wake rhythm misalignment and insufficient sleep on these associations in 10-years-wide age-groups. Circadian type was assessed with the widely-used single item for self-assessed morningness/eveningness from the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ). RESULTS: Evening-types, especially definite evening-types, were more exhausted and had poorer working ability than morning-types. Higher exhaustion among evening-types was apparent in all working ages with a peak at ages 45 to 54 years. Poorer working ability in definite evening-types as compared to definite morning-types was found only at ages 35 to 54 years. Evening-types, especially definite-evening-types, had also more social jet lag and they reported more insufficient sleep than definite morning-types. More frequent insufficient sleep associated with poorer working ability and partly mediated the association between circadian type and working ability. CONCLUSION: Circadian phenotypes were found to differ in risk for exhaustion and in working ability, and this association was partly mediated by insufficient sleep. Our findings emphasize the importance to improve sleep especially among evening-types to ensure better work wellbeing.