Objectives This is the first general population study to evaluate whether evening chronotypes (E) have poorer work ability (WA) and higher probability for early disability pensions (DPs) than morning types (M) in middle age.
Methods Among non-retired individuals (n=5831; 2672 men, 3159 women) of the Northern Finland Birth Cohort 1966, chronotype was determined at the age of 46 years with shortened Morningness–Eveningness Questionnaires in 2012. The outcomes were poor WA in 2012, indicated by scores 0–7/10 of Work Ability Score, and registered emergence of DPs in 2013–2016. Multivariate logistic and Cox regression analyses were separately adjusted for factors related to sleep, health and behaviours, sociodemographic and economic factors, or working times.
Results E-types represented 10% (n=264) of men and 12% (n=382) of women. Compared with M-types, the unadjusted ORs with 95% CIs of poor WA for E-type men and women were 2.24 (95% CI 1.62 to 3.08) and 2.33 (95% CI 1.74 to 3.10), respectively. The odds remained statistically significant and approximately twofold in all separate adjustment models tested. During 2013–2016, 8 (3.0%) E-type men and 10 (2.6%) E-type women were granted DP, which, compared with M-types, represented a higher HR that was statistically significant for men (HR 3.12, 95% CI 1.27 to 7.63) and remained significant except when multiple sleep variables or working times were adjusted for.
Conclusions Eveningness appears a previously unrecognised risk factor for poor WA and early disability. We suggest that individual chronotype be considered in attempts to lengthen work careers.
- circadian rhythm
- disabled persons
- occupational health
- longitudinal studies
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Contributors TR, HJ and LA-M presented the study hypothesis and the medical background for it, after which all authors participated in the study design, led by LA-M as the guarantor of the study. IN performed the statistical analyses and created the figure and quality control of data, and algorithms were performed by all authors. The tables were created by TR, IN and LA-M. TR wrote the first draft of the manuscript. All authors interpreted the data and revised the manuscript carefully. All authors approved the final version of the manuscript, and TR had the final responsibility to submit the manuscript.
Funding This study is funded by European Regional Development Fund (539/2010 A31592), Oulun Yliopisto (24000692), Oulu University Hospital (24301140) and OP Group Research Foundation.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. NFBC data are available from the University of Oulu, Infrastructure for Population Studies. Permission to use the data can be applied for research purposes via electronic material request portal. In the use of data, the university follows the EU general data protection regulation (679/2016) and Finnish Data Protection Act. The use of personal data is based on cohort participant’s written informed consent at his/her latest follow-up study, which may cause limitations to its use. Please contact NFBC project centre (NFBCprojectcenter@oulu.fi) and visit the cohort website (www.oulu.fi/nfbc) for more information.