- What Is Circadian Rhythm?
- Take our Sleep Habits Test
- Find a sleep therapist near me
Key points
- The U.S. House passed a bill to require permanent daylight savings time.
- Medical associations recommend permanent standard time.
- Standard time is more aligned with circadian biology and is linked to fewer health problems.
For years, sleep scientists have documented many problems with daylight saving time (DST), which requires changing clocks twice a year. After time changes, incidences of adverse cardiovascular events and mood disorders increase, and the frequency of vehicular crashes rises. Our bodies are entrained by daily light and dark periods, and even the one-hour shift in timing of sunrise and sunset can disrupt the circadian system. Schools and businesses do not adjust start or end times on transitions. Changing the clocks on Sunday is meant to ease the time transition, but one day is not enough time to be effective.
After reviewing years of study, a panel of 23 scientists published a paper that laid out the evidence for permanent standard time (Rishi et al. 2020). Both the American Academy of Sleep Medicine and the American Medical Association favor permanent standard time. The problem with DST is that it is inconsistent with circadian physiology. Late evening light, along with early morning darkness, causes a phase delay in the endogenous system. Chronic misalignment has been associated with increased risk of obesity, metabolic syndrome, heart disease, and depression. The misalignment is worst in the westernmost areas of time zones where sunset occurs later in clock time.
During the OPEC oil embargo of 1973-74, the U.S. enacted permanent DST and then dropped it after only one winter because of widespread dissatisfaction primarily due to having to wake up in darkness to get to work or to school. In a post I wrote in 2021, I described the origin of DST when in 1916 the German Empire pushed clocks forward by one hour to save fuel. The UK and France did so a few weeks later, and the U.S. two years later in 1918 after joining the war in 1917.
Then DST was repealed later in 1918 when the war ended. During WW2, the U.S. reestablished DST in 1942, then abandoned it when the war ended in 1945. In 1966, the U.S. established rules allowing states to introduce DST in Spring and change back to ST in the Fall. The ensuing years led to a patchwork of different plans across the country. Currently, only Arizona and Hawaii keep ST year-round, with the rest changing twice a year.
Legislation has been introduced in many states opting for permanent DST or ST, and on July 14, the U.S. House of Representatives passed a bill to require permanent DST throughout the U.S. The vote was 308-117. The bill would allow states to opt out if their legislatures pass laws before the House bill is enacted. Several senators have, however, said that it will likely not be passed in the Senate. Why the House chose to ignore the recommendations of AASM and AMA is a mystery, since both organizations consulted with House members.
One of the most problematic aspects of year-round DST is its effect on children having to wake and go to school long before sunrise. You can see the effect by looking at sunrise and sunset times on each day of the year where you live. For example, in Denver, Colorado, on October 5, 2026, sunrise is at 7:00 AM. With permanent DST, sunrise would be at 8:00 AM, with many children waiting for buses in the dark. If you have an opinion about whether the U.S. should keep the current DST-ST switch or change to permanent DST or ST, now is the time to contact your Representative and your two state senators to convey your views.
- What Is Circadian Rhythm?
- Take our Sleep Habits Test
- Find a sleep therapist near me
References
Rishi, M., Ahmed, O., Barrantes Perez, J. et al. Daylight saving time: an American Academy of Sleep Medicine position statement. J Clin Sleep Med 16, 1781–1784 (2020). https://doi.org/10.5664/jcsm.8780
