News & Views

How sleep is affected by seasonal time changes

By Zach Pearl, PhD Staff


Transitions into and out of Daylight Saving Time (DST) change the social and environmental timing and therefore affect millions of people annually1. DST consists in a shift forward of 1-hour during spring, which increases the available daylight in the evening, and a shift backward of 1-hour during fall which increases the available daylight in the early morning.
The idea behind it is to improve the match between daylight hours and people’s activity peaks. The clock change causes a sudden shift in the external cues which help our internal body clock to maintain a 24-hour track. It can take several days for our biological clock to re-synchronize with the new schedule. For some people, this clock’s desynchronization may lead to disrupted sleep, daytime tiredness and health problems.

Daylight Saving Time change disrupts sleep

It has been known since the 1970s that DST transitions disrupt sleep for up to 1 week following the local clock change. The impact is mainly on sleep continuity and sleep efficiency2. There is a growing effect of sleep loss at both transitions (back and forth) as bed and rise times are gradually adjusted to the newly imposed clock time3. However it was shown in several studies that our biological clock adjusts more easily to a phase delay (autumn change) than a phase advance (spring transition)4. The effect of these clock adjustments is similar to the effects of jet lag or shift work which can reduce mental sharpness and increase the risk of numerous diseases and sleep disorders5.

Time change disrupts health

  • Heart attack – There are several evidences showing a brief increase in the frequency of heart attacks after time change in the spring, as well as a decrease in heart attacks after returning to standard time in the fall6
  • Car/Workplace accidents– It is expected that the changes to and from DST could affect driving safety. However, the data on this is controversial, where some studies show an increase in car or workplace accidents after the time change7 8 and other show no correlation with it9 10
  • Suicides/Psychiatric illness – The results here are also controversial where some studies suggested that there is an increase in the incident of suicides or psychiatric illness5 while others showed no significant effect11

How to deal with Daylight Saving Time transition

  • Gradual transition into the time change – Individuals who normally have poor quality of sleep, or less than ideal sleep duration, are likely to be at risk. Ensuring adequate opportunity for sleep in the week before may help in preparation for the time transitions3
  • Give yourself a sleep break after the time change – If you feel sleepy after the change to Daylight Saving Time, take a short nap in the afternoon, but not too close to bedtime
  • Keep regular sleep hours – Keep bed and wake up time at the same time each day. This helps your body regulate its sleep pattern and get the most out of the hours you sleep
  • Go outside – Light suppresses the secretion of the sleep-inducing hormone melatonin. Therefore it is important to expose yourself to the light during the waking hours as much as possible, and vice vera, do not expose yourself to bright light when it is dark outside. This will help adjust the body’s circadian rhythm
  • Get up if you can’t sleep – If you’ve been awake for more than 20 minutes, get up, go to another room, and do something relaxing to help you get drowsy. Keep the lights low

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