The transition from daylight saving time to standard time increases the risk of depression

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daylight saving time

“The year has 16 months: November, December, January, February, March, April, May, June, July, August, September, October, November, November, November, November,” writes the Danish poet Henrik Nordbrandt in a disheartening comment on the month people are about to enter.

And Nordbrandt is not the only one suffering in November.

A recently published study documents that the number of people who are diagnosed with depression at psychiatric hospitals in Denmark increases immediately after the transition from daylight saving time to standard time.

More specifically, the number of depression diagnoses during the month after the transition from daylight saving time is approximately 8% higher than expected based on the development in the number of diagnoses up to the transition.

The study is based on analysis of 185,419 depression diagnoses registered in The Central Psychiatric Research Register between 1995 and 2012.

According to the researchers from Aarhus University Hospital, the increase in depression rates is too pronounced to be coincidental.

They 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.

Researchers also points out that even though the study is based on analysis of relatively severe depressions diagnosed at psychiatric hospitals, there is no reason to believe that the time transition only affects the propensity to develop more severe forms of depression.

The study does not identify the underlying mechanism triggering the marked increase, but 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 – 6:00 pm to the morning between 7:00 am – 8:00 am.

People probably benefit less from the daylight in the morning between 7-8 am, because many of them are either in the shower, eating breakfast or sitting in a car or bus on the way to work or school.

When they get home and have spare time in the afternoon, it is already dark.

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.

Why are the results of the study important? The researcher from Aarhus University is not in doubt:

“The 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.”

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Citation: Hansen BT, et al. (2016). Daylight savings time transitions and the incidence rate of unipolar depressive episodes. Epidemiology, published online. DOI: 10.1097/EDE.0000000000000580.
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