Daylight savings time (DST) heralds longer days, more sun, and warmer temperatures, but did you know that it is also associated with an increased risk of fatal car accidents? Multiple sleep research studies have found a higher rate of car accidents on the Monday following the shift to Daylight Savings Time. The same association is not found with the Autumn time shift. But what's behind the statistics? To fully grasp the problem and how we can manage it, we need an understanding of our internal body clocks.
Our bodies are naturally programmed to have daily cycles, called circadian rhythms, that govern many mental and physiological domains. For the sake of this discussion, let's say that you typically have the common sleep schedule of an 11 p.m. - 12 midnight bedtime and a 6-8 a.m. rise time. The graphic below represents how your alertness would fluctuate throughout the day on such a schedule:
As you can see, there are separate alertness peaks mid-morning and in the late evening. Most people who keep the above sleep schedule will be maximally alert somewhere around 9 p.m.
It makes sense that our circadian rhythms are not fixed; otherwise, we'd never be able to adapt to new locations in different time zones. But circadian rhythms change relatively slowly and, for unclear reasons, it's easier to "phase delay" our rhythms (be able to stay up later) than "phase advance" (be able to go to bed earlier); in general, it takes us 50% longer to adjust to phase advances than delays. The rule of thumb is that it we can phase advance approximately one hour per day.
During DST, we are asking our bodies to phase advance. Instead of going to bed at 11 p.m. when our bodies are naturally sleepy, we try to go to bed at the new 11 p.m. clock time but our bodies still think it's 10 p.m.! At 10 p.m., we are still coming off our maximal alertness peak and falling asleep is likely to be difficult. Couple this problem with the possibility that we just lost an hour of sleep with the time change due to having to get up for our usual Sunday responsibilities, and it can be a dangerous combination leading to significant sleep deprivation on Monday morning.
To ensure a smooth transition through DST, the following countermeasures may be helpful:
Author: Joseph Krainin, M.D., FAASM is the Founder and Owner of Singular Sleep, LLC, an innovative comprehensive online sleep clinic. A graduate of the renowned Michael S. Aldrich Sleep Disorders Center at University of Michigan, Dr. Krainin is a fellow of the American Academy of Sleep Medicine and board certified in both Sleep Medicine and Neurology.
© 2021 American Sleep Association.