Psychiatric hospitals see an increase in depression cases immediately after the transition from daylight saving time to standard time, according to a new study in Denmark.
The findings, based on an analysis of 185,419 depression diagnoses filed in the Central Psychiatric Research Register, show that Danish depression cases jump approximately eight percent the month right after the transition from daylight saving time. The study involved data from the years 1995 to 2012.
This increase in depression rates is too pronounced to be coincidental, note the researchers.
“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,” says Associate Professor Søren D. Østergaard at Aarhus University Hospital in Risskov, which is part of the Department of Clinical Medicine at Aarhus University.
Østergaard is one of five researchers who conducted the study, a collaboration between the departments of psychiatry and political science at the universities of Aarhus, Copenhagen and Stanford.
While the study is based on an analysis of relatively severe depression diagnosed at psychiatric hospitals, Østergaard says there is no reason to believe that the time transition only affects the tendency to develop more severe forms of depression.
“We expect that the entire spectrum of severity is affected by the transition from daylight saving time to standard time, and since depression is a highly prevalent illness, an increase of eight per cent corresponds to many cases”, says Østergaard.
Although the study does not identify the underlying mechanism behind the increase, the researchers point to some possible causes. In Denmark, the transition from daylight saving time to standard time “moves” one hour of daylight from the afternoon between 5:00 pm to 6:00 pm to the morning between 7:00 am to 8:00 am.
“We probably benefit less from the daylight in the morning between seven and eight, because many of us are either in the shower, eating breakfast, or sitting in a car or bus on the way to work or school. When we get home and have spare time in the afternoon, it is already dark,” explains 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. This is especially true for people with a tendency towards depression — as well as their relatives. Furthermore the healthcare professionals who diagnose and treat depression should also take our results into consideration,” says Østergaard.
Source: Aarhus University