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The springtime change may adversely affect patterns of mortality.

Car accidents increase in the weeks following the start of daylight saving time.

Maintenance of good sleep habits can defray the sometimes difficult adjustment to time changes.

March means the start of Daylight Saving Time and the time of year between spring and fall when clocks are set one hour ahead. Congress passed An Act to Save Daylight and to Provide Standard Time for the United States on March 19, 1918. The law, now more commonly known as the Standard Time Act of 1918, established current standard time zones in the U.S. and followed precedent in Europe, where some countries had already adopted Daylight Saving Time. Over time, revisions have occurred, and changes have been proposed, but elements of the original legislation remain in place today.

For many, this annual transition is rote and routine, but most people find the single-hour advance exhausting. Many note that the acclimation period needed lingers for days before fully adjusting. At least 54 percent of the public supports ending daylight saving time, and over half experience tiredness following the spring clock change. Beyond the fatigue, the springtime change may have significant effects on physical and mental health.

A 2024 study in BMJ Medicine examined the transition to daylight savings time and associated risks of all-cause and specific mortality in the U.S. Between the start of 2015 and the end of 2019, 13,912,837 deaths were recorded and analyzed for cause, including Alzheimer’s disease, cardiovascular disease, respiratory disorders, and cancer. The time change was found to be influential for patterns of mortality; in particular, a protective effect of the autumn time change was noted with a significant decrease in all causes of death during the first eight weeks following the transition. However, no effect of the time change on the overall number of deaths was observed.

Does the daylight saving time change affect mood or risk of self-harm? Results are mixed, and the impact of daylight savings time on mental health outcomes is an active topic of study. An analysis in the European Journal of Public Health from 2024 showed no increase in suicide in Austria, Switzerland, and Sweden following the start of daylight saving time. However, data vary, and studies show that some subgroups, including patients with substance use disorders, may incur a 6.59 percent increase in suicide risk soon after the springtime change.

The biannual time change has societal consequences. For example, work productivity declines in some sectors with the springtime change. One of the best studied population-level outcomes is fatal motor vehicle collisions. The change in light conditions in spring and fall may be expected to influence the incidence of accidents. In a 2025 study of fatal crashes occurring from 2010-2019, fatal crashes decreased by 7.1 percent in the five weeks following the autumn time change but increased by 12 percent in the five weeks after the spring time change. Correspondingly, pedestrian and bicycle collisions increased in incidence after the autumn time change and decreased in the spring. The amount of ambient light may have been a contributing factor.

Good habits are powerful armor to cope with the time change. Experts recommend close attention to sleep hygiene with avoidance of caffeine or other stimulants and adoption of a regular bedtime and wake-up time on all days of the week (yes, even weekends). It is best to reduce or even eliminate screen time in the hour before bedtime. Natural light has the greatest influence on helping to reset biorhythms. Taking a walk or opening curtains to allow for direct sun exposure often speeds up adjustment.

The physical, psychological, and societal consequences of a biannual time change are increasingly evident in research. Some may wonder why something as simple as the passing of time remains grounded in a law more than a century old. But the transition need not be so onerous. Knowledge and practice of healthy behaviors can mitigate weariness so that we all sleep better at night. We’re all on the clock, after all.

Why Is Sleep Important?

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