Background: Daylight savings time transitions affect approximately 1.6 billion people worldwide. Prior studies have documented associations between daylight savings time transitions and adverse health outcomes, but it remains unknown whether they also cause an increase in the incidence rate of depressive episodes. This seems likely because daylight savings time transitions affect circadian rhythms, which are implicated in the etiology of depressive disorder. Therefore, we investigated the effects of daylight savings time transitions on the incidence rate of unipolar depressive episodes.
Methods: Using time series intervention analysis of nationwide data from the Danish Psychiatric Central Research Register from 1995 to 2012, we compared the observed trend in the incidence rate of hospital contacts for unipolar depressive episodes after the transitions to and from summer time to the predicted trend in the incidence rate.
Results: The analyses were based on 185,419 hospital contacts for unipolar depression and showed that the transition from summer time to standard time were associated with an 11% increase (95% CI = 7%, 15%) in the incidence rate of unipolar depressive episodes that dissipated over approximately 10 weeks. The transition from standard time to summer time was not associated with a parallel change in the incidence rate of unipolar depressive episodes.
Conclusion: This study shows that the transition from summer time to standard time was associated with an increase in the incidence rate of unipolar depressive episodes. Distress associated with the sudden advancement of sunset, marking the coming of a long period of short days, may explain this finding. See video abstract at, http://links.lww.com/EDE/B179.
From the aDepartment of Political Science, University of Copenhagen, Copenhagen, Denmark; bDepartment of Political Science, Stanford University, Stanford, CA; cDepartment of Political Science, Aarhus University, Aarhus, Denmark; dPsychiatric Center Copenhagen, Copenhagen University Hospital, Copenhagen, Denmark; eDepartment of Clinical Medicine, Aarhus University, Aarhus, Denmark; and fPsychosis Research Unit, Aarhus University Hospital, Risskov, Denmark
Submitted 9 December 2015; accepted 18 October 2016.
The study was funded by grants from the Carlsberg Foundation (Grant Numbers: 2011_01_0609 and CF14-0703). Søren Dinesen Østergaard was supported by a grant from the Lundbeck Foundation (Grant Number: R165-2013–15320). The funders had no influence on design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
The authors declare no conflicts of interest.
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Correspondence: Søren Dinesen Østergaard, Psychosis Research Unit, Department of Clinical Medicine, Aarhus University Hospital, Risskov, Skovagervej 2, 8240 Risskov, Denmark. E-mail: firstname.lastname@example.org.