The Clouded Harms of Clock Changes
A new study shows that even minor, one-hour clock changes can negatively affect daily functioning and quality of life.
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Every March, I dread losing sleep as our clocks spring forward into daylight saving time, already yearning for when they fall back in November. Daylight savings is a known disruptor of humans’ built-in biological clock called the circadian rhythm, which maintains essential bodily functions including our sleep-wake cycle.
Under federal law, daylight savings starts at 2 AM on the second Sunday of March and ends at 2 AM on the first Sunday of November. First introduced in 1918 to reduce energy costs during World War I by extending daylight hours, about one-third of the world still practices daylight savings.
However, global research has shown the health harms underlying clock changes. Immediate health effects include sleep deprivation, fatigue, and blood pressure changes. In the days following the start of daylight savings, there is a 6% increase in fatal car accident risk and a 24% increase in heart attack risk.
Gonzalo Labarca and team observed 30 healthy young men in Los Angeles, Chile to determine the short-term health effects of clock changes. Participant health was assessed 2 weeks before and after the fall and spring transitions using sleep questionnaires and computerized tasks to measure reaction and response times.
The results reveal a reduction in participants’ total sleep time after both transitions. Sleep quality worsened after the fall transition, and participants reported taking longer to fall asleep. The spring transition caused greater disruption to circadian rhythms and slower reaction times on computerized tasks. The findings highlight how even minor, one-hour clock changes can impact daily functioning and quality of life.
Though Chile is the only South American country with daylight savings, 70 countries worldwide and 48 U.S. states still observe the time change. The Sunshine Protection Act (2023) was proposed to implement a federal permanent standard time for the U.S, but it’s had little traction in Congress. In 2024, the American Academy of Sleep Medicine publicly called for eliminating seasonal time changes due to their negative health effects. Each year, state lawmakers advocate for permanent time in the hopes this will finally be the year we let go of clock changes, and gain back that precious hour of sleep.
