Sleep expert explains the science behind the fall time change

Sleep expert explains the science behind the fall time change

When clocks fall back this weekend, we’ll gain an hour — but does that necessarily mean better sleep? Hannah Peach, a sleep health expert at UNC Charlotte, explains how the change from daylight saving time back to standard time affects our internal body clocks, why the fall transition is easier on our bodies than the spring change and how shorter days can affect our well-being. She also explains why permanent standard time may be the healthier option, particularly for children and adolescents.

We gain an hour when clocks fall back. Does that actually mean we get an extra hour of beneficial sleep?

We certainly get the opportunity to sleep an extra hour when clocks fall back, but that doesn’t necessarily mean we get an extra hour of quality sleep! Our bodies don’t know the clocks have changed; for individuals with consistent sleep patterns and a strong circadian rhythm, this time change may simply lead to waking up an hour earlier than usual. This can be especially true for children.

What happens to our internal body clock when daylight saving time ends?

Again, our circadian rhythms don’t know the clocks have changed. For people who do not regularly get enough sleep, this may be a welcome and beneficial extra hour of sleep. For others, naturally waking up according to their body’s internal clock (but an hour earlier than normal) gives an extra hour on Sunday to be productive or enjoy the weekend.

Is the fall time change easier on our bodies than the spring change?

Yes, the fall time change is much easier on our bodies than the spring change. Losing an hour of sleep in the spring can increase sleep deprivation and corresponding negative outcomes, such as drowsy driving and impaired cognition. In fact, a study by Cho and colleagues (2017) found that judges hand out harsher punishments and longer sentences following spring daylight savings due to sleep deprivation. (Cho, K., Barnes, C. M., & Guanara, C. L. (2017). Sleepy punishers are harsh punishers. Psychological Science, 28(2), 242–247. https://doi.org/10.1177/0956797616678437)

How might the time change affect our mood, concentration and energy levels?

The spring change can negatively impact mood, concentration and energy levels by increasing sleep deprivation. The fall change shouldn’t lead to sleep loss, but it may impact other aspects of wellness, such as seasonal depression because of shorter days with less sunlight.

How long should the adjustment take, and when should people be concerned about ongoing sleep problems?

Sleep needs and timing vary widely from person to person, but most individuals should adjust to the time change within one to two weeks. Problems typically occur when our body’s internal clock does not match our work or school schedules. 

From a sleep-health perspective, would permanent standard time or permanent daylight saving time be better for us?

From a solely sleep-health perspective, permanent standard time would be beneficial, especially for children and adolescents (e.g., Medina et al., 2015). As many parents would likely report, the time change can be extremely disruptive to their children’s sleep schedules. (Medina, D., Ebben, M., Milrad, S., Atkinson, B., & Krieger, A. C. (2015). Adverse Effects of Daylight Saving Time on Adolescents’ Sleep and Vigilance. Journal of Clinical Sleep Medicine, 11(8), 879–884. https://doi.org/10.5664/jcsm.4938)

Written by: Hannah Peach and Jason Vaughan