Q&A: Should the US continue twice-yearly clock changes?

Key takeaways:

• There is debate on whether the U.S. should a adopt a permanent standard time to avoid potential health risks.
• An expert suggests shortening the current period of daylight saving time to create a better balance.

An emerging body of research suggests that twice-yearly clock adjustments may have negative impacts on health, leading some experts to advocate for a permanent time.

In 2023, the American Academy of Sleep Medicine (AASM) issued a position statement advocating for a year-round standard time (ST), which the organization said aligns best with human circadian biology.

In its statement, which was endorsed by 20 other medical, scientific and advocacy organizations, AASM cited evidence that supported benefits of ST for health and safety with respect to sleep cycles, motor vehicle accidents as well as related injuries and fatalities and acute cardiovascular events.

Others, however, disagree with adopting a permanent ST. José María Martín-Olalla, PhD, assistant professor and physicist at the University of Seville in Spain, coauthored a response to AASM, published in the Journal of Clinical Sleep Medicine, that states conversations regarding the adoption of a permanent ST “requires a fair balance of the cons and pros of the practice.”

Healio spoke with Martín-Olalla to learn more about his perspective on the social, cultural and health benefits of maintaining the status quo on changing clocks in the United States and around the world.

Healio: What factors and experiences led you to advocate for clock changes as opposed to a permanent ST?

Martín-Olalla: I maintain that the current seasonal DST setting is not artificial and does not play against human physiology. Rather, it was designed to align with human physiology. Morning light is a key cue to synchronize human rhythms with the solar day, as physiologists explain; the current seasonal DST just aligns social time with the sunrise.

Modern societies have rigid preset schedules which do not accommodate well with the varying sunrise time. Seasonal DST just helps align our morning schedules with the sunrise. Think of a regular 9 a.m. to 5 p.m. working schedule; currently it’s 9 a.m. to 5 p.m. in winter, and 8 a.m. to 4 p.m. in summer (rendered as 9 a.m. to 5 p.m. in DST). We just adapt human activity to seasons, much like in ancient times and like we adapt our wardrobe.

Healio: Please briefly address the benefits and risks in adopting permanent ST and whether the U.S. should adopt it.

Martín-Olalla: I do not see any specific benefit in adopting permanent ST, which means delaying human activity in spring and summer, when the sun rises the earliest. Instead, I see some inconveniences.

Seasonal DST was a solution to a problem in the 1920s: the late timing of human activity in summer. Throw away the solution, you get the problem back. People will find 1 hour less spare time in daylight during spring-summer. It is a sensible 12.5% reduction if spare time equals 8 hours per day. People will react to that.

The response may consist in giving birth to seasonal schedules, with their transition dates. They are currently almost unnecessary thanks to the seasonal clocks. Seasonal schedules are less efficient than seasonal clocks due to lack of synchronization.

If seasonal schedules do not gain popularity, then consider the following risk. With permanent ST, people will find outcomes in advancing their activity in summer because the sun will rise earlier. This will continue through winter and will increase the number of early risers. You set clocks to permanent ST and may end up with a permanent-DST-like activity. For 100 years, the current setting in the U.S. has successfully restrained the incorporation of human activity to the dark hours of the morning winter, in line with human physiology and human health.

Healio: Can you compare and contrast the impact of DST among smaller nations of Europe compared with a large country such as the U.S.?

Martín-Olalla: In Europe, the Central European Time zone (UTC+1) spans more than two physical time zones. Countries on the east side of the time zone tend to do things earlier than those on the west side. Each country develops their own schedules based on the sun clock.

If we look at the size of the largest Western European countries (France and Spain), they match the size of one American time zone. If we place the easternmost point of Spain on Boston, then the westernmost point is located west of Detroit. Same goes with France.

When it comes to DST, I understand that large areas like a U.S. time zone or a European country like Spain or France benefit from the current setting. The eastern side of a time zone is set to a “late” timing and the western side to a “early” timing, relative to each other. The current seasonal clocks make the timing not too early in the west during the winter (if permanent DST is chosen) and not too late in the east during the summer (if permanent ST is chosen). When a choice is demanded, you get the usual claims at either side: “the sun will rise at 9 a.m. in Indianapolis if permanent DST is chosen!” and “the sun will rise at 4 a.m. in Boston if permanent ST is chosen!”

Five hours is a formidable range for this critical time of day.

Healio: What do you believe would be the health and social impact of a potential permanent change to DST?

Martín-Olalla: I understand that permanent DST will play against human physiology in populations that face morning darkness during a few months.

I do advocate to shortening the current period of DST and break even the year. If permanent DST materializes, a critical issue is whether the number of people at discomfort will be high enough to overturn the new setting. Socially, people may also react to permanent DST by delaying their winter social schedules, but this, also, is easier said than done.

In a battle of early risers and late risers, I prefer a compromise. Keeping in mind that seasons will continue to exist, the current alternating clocks provide a smart synchronizing mechanism to adapt human activity to seasons, to prevent early risers from becoming too early in winter, and to prevent late risers from becoming too late in summer.

References:

• Martín-Olalla JM, Mira J. J Clin Sleep Med. 2024;doi:10.5664/jcsm.11042.
• Rishi MA, et al. J Clin Sleep Med. 2023;doi:10.5664/jcsm.10898.

For more information:

José María Martín-Olalla, PhD, can be found on X at: @MartinOlalla_JM.