News & Views

Seasonal Time Changes – How do they affect our Sleep & Health?

By Zach Pearl, PhD Staff


Daylight Saving Time (DST) was introduced at the beginning of the 20th century with the idea of giving people “more light to enjoy”. It fits closely with today’s hectic 24/7 lifestyle and at the same time demonstrated to save electricity. DST consists of a shift forward of 1-hour in spring time (March), increasing available daylight in the evening, and a shift backward of 1-hour in fall time (October), increasing available daylight in the early morning.

Daylight Saving Time change disrupts sleep

Transitions into and out of Daylight Saving Time (DST) change the social and environmental timing and therefore affect millions of people annually 1 . The clock change causes a sudden shift in the external cues which help our internal body clock to maintain a 24-hour track.

It has been known since the 1970s that DST transitions disrupt sleep, in some people, for up to 1 week following the local clock change. The impact is mainly on sleep continuity and sleep efficiency 2 . 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 time 3 . Several studies have shown that our biological clock adjusts more easily to a phase delay (autumn change) than a phase advance (spring transition) 4 .

Recent research showed that people who tend to be so-called short sleepers, logging < 7.5 hours a night, and early risers (known as larks), have the most trouble adjusting to the new schedule 5 .

How does it affect our health?

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 disorders 6 .

  • Heart attack – Several studies have demonstrated an increase, albeit brief, in the frequency of heart attacks, especially on the Sunday after DST and more so in women 7 8
  •  Car/Workplace accidents– Data is conflicting, where some studies show an increase in car or workplace accidents after the time change 9 10 and other show no correlation with it 11 12
  • Suicides/Psychiatric illness – Conflicting results where some studies suggested that there is an increase in the incident of suicides or psychiatric illness 6 while others showed no significant effect 13
  • Vigilance – Significantly deteriorated in adolescents and high school students, with a decline in Psycho-motor Vigilance Test (PVT) performance, resulting in longer reaction times 14 .

Tips & Tricks – How to best deal with DST transition?

  •  Prepare your body for the change – If you suffer from insomnia, maintaining basic sleep hygiene including reducing/eliminating caffeine and alcohol, exercising several hours before bedtime, creating calming rituals (mediation, breathing) before bed time to gradually relax yourself
  • Give yourself “a break” – If you feel sleepy after the change to DST, take a short nap in the afternoon, though not too close to bedtime
  • Stick to your schedule – Maintain bed and wake up time at the same time each day. It helps your body regulate its sleep pattern and get the most of your sleep
  • Go outside – Light suppresses the secretion of the sleep-inducing hormone melatonin. Exposing yourself to the light during the waking hours as much as possible, and conversely, less bright light when it is dark outside

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