: A change toward Eveningness in circadian sleep-wake behavior is generally seen from childhood to adolescence, but less is known about circadian changes during adulthood. Circadian changes during mid-adulthood are of high interest, since Eveningness associates with a range of health-related problems, including psychological symptoms and mental disorders. In this study, we examined the circadian stability across 10 years, from 42 to 52 years of age, and how it is associated with sleep and mental health in a Finnish general population cohort follow-up-based (= 976).: Circadian type was assessed at both ages with a widely used item for self-estimated Morningness/Eveningness from the original Horne-Östberg Morningness-Eveningness Questionnaire. Generalized estimating equations were used for analyzing how a change in Morningness/Eveningness was associated with sleep and mental health longitudinally.: Our findings indicate that the circadian type is a highly stable trait during mid-adulthood with mainly moderate changes occurring in 42.2% of adults and no circadian change among 57.8% of adults. Most changes occurred within the same circadian type (23.9%), second to changes between moderate circadian types (13.3%). Changes between the Definite Evening-types and Morning-types were very rare (0.5%). Stable Evening-types reported more insufficient sleep, discrepancy between sleep duration on workdays and free days, and depression as compared to stable Morning-types. Moderate changes toward Morningness, comprising mostly those within Morning-types, were associated with reduced distress and psychological symptoms.: In conclusion, our findings show high stability of mid-adulthood circadian type. However, changes toward Morningness seem to be associated with improved mental health. (PsycInfo Database Record (c) 2024 APA, all rights reserved). Objective n Method Results Conclusions
