The transition from daylight saving time to standard time is associated with an increase in the incidence rate of unipolar depressive episodes, researchers reported in Epidemiology.
Daylight saving time transitions affect circadian rhythms, which are involved in the etiology of depressive disorder, noted Associate Professor Søren D. Østergaard, from Aarhus University Hospital in Risskov, Denmark, and colleagues. The group compared the observed trend in the incidence rate of hospital contacts for unipolar depressive episodes after transitions to and from daylight saving time with the predicted trend in the incidence rate. The study is based on analysis of 185,419 depression diagnoses registered in the Central Psychiatric Research Register between 1995 and 2012.
The researchers found that the transition from daylight saving time to standard time was associated with an 11% increase in the incidence rate of unipolar depressive episodes, which lessened over 10 weeks. However, the transition from standard time to daylight saving time was not associated with a similar change in the incidence rate of unipolar depressive episodes.
“We are relatively certain that it is the transition from daylight saving time to standard time that causes the increase in the number of depression diagnoses and not, for example, the change in the length of the day or bad weather. In fact, we take these phenomena into account in our analyses,” stated Professor Østergaard. “Furthermore, the transition to standard time is likely to be associated with a negative psychological effect, as it very clearly marks the coming of a period of long, dark, and cold days.”
“Our results should give rise to increased awareness of depression in the weeks following the transition to standard time,” Professor Østergaard continued. “This is especially true for people with a tendency toward depression, as well as their relatives. Furthermore, the healthcare professionals who diagnose and treat depression should also take our results into consideration.”