The Clock Change Explained (And Why Sleep Scientists Recommend Stopping It)

Twice a year, we collectively agree to mess with time itself. In spring, we "spring forward" and lose an hour of sleep. In the fall, we "fall back" and gain one. It's called Daylight Saving Time, and if you've ever wondered why we do this annoying ritual, you're not alone.

Spoiler alert: the reasons we started doing it don't really apply anymore, and the science shows it might actually be hurting us.

The Origin Story: War, Farming, and Energy

The idea of shifting clocks around started getting serious attention in the early 1900s. Germany was the first country to adopt it in 1916 during World War I, trying to conserve fuel for the war effort. The logic was simple: if you shift an hour of daylight to the evening when people are awake and active, they'll use less artificial lighting and save energy.

The United States jumped on board in 1918 for similar reasons. Then it got repealed. Then it came back during World War II. Then it became a confusing mess where different states and cities did their own thing. Finally, in 1966, Congress passed the Uniform Time Act to standardize it (though states could still opt out, and Arizona and Hawaii did).

Here's a myth worth busting right away: Daylight Saving Time was NOT created to help farmers. In fact, farmers generally hated it because their work is tied to actual sunlight and animal schedules, not whatever arbitrary time we put on clocks. Cows don't care if you changed your clock. They want to be milked when they want to be milked.

Does It Actually Save Energy?

This was the whole point, right? So does it work?

Sort of, but not really, and definitely not as much as it used to.

Studies show that Daylight Saving Time does reduce electricity used for lighting, but the effect is pretty small, only about 1% of total energy use. And here's the kicker: any energy saved on lighting can be offset by increased use of air conditioning (because people are awake during warmer evening hours) or heating (in the spring when mornings are colder).

Back when DST started, lighting was a huge chunk of energy consumption. Today? Not so much. We have LED bulbs, better insulation, and a ton of energy goes to things like computers, phones, and appliances that run 24/7 regardless of what the clock says.

A 2008 study in Indiana (which had recently adopted DST statewide) found that the time change actually increased overall energy use by about 1% because of heating and cooling costs. So much for that.

The Health Costs Are Real

Here's where things get concerning. Scientists have found that messing with our sleep schedules twice a year has genuine health consequences.

Heart attacks increase. Multiple studies have found a spike in heart attacks in the days following the spring time change when we lose an hour. One analysis found a 24% increase in heart attacks on the Monday after springing forward. The fall time change (when we gain an hour) shows a corresponding decrease, suggesting the disruption itself is the problem.

Car accidents go up. The Monday after we spring forward sees about a 6% increase in fatal car accidents. Sleep deprivation and disrupted circadian rhythms make people worse drivers.

Strokes increase. Research shows an 8% increase in stroke risk in the two days after either time change, with even higher rates in people over 65 and those with cancer.

Productivity drops. Studies have found increased workplace injuries, decreased productivity, and more "cyberloafing" (slacking off online) in the days after the time change.

Mental health takes a hit. Some research links the time changes to increases in depression and seasonal affective disorder, particularly in the fall.

Your Circadian Rhythm Is Not a Fan

Your body runs on an internal clock called your circadian rhythm. It regulates sleep, hormone release, body temperature, and other functions based on light and dark cycles. When you suddenly shift your schedule by an hour, your circadian rhythm doesn't just adjust instantly. It can take days or even weeks to fully adapt.

This is basically like giving the entire population mild jet lag twice a year. And unlike actual jet lag from travel, we can't just accept that we'll be tired for a few days because we got to visit somewhere cool. We're tired because... we decided to be tired. Teenagers are especially affected. Your natural sleep patterns already shift later during adolescence (which is why early school start times are rough). Adding a time change that takes away an hour of sleep in the spring makes this worse. Studies show increased sleepiness, decreased attention, and worse academic performance after the springtime change.

The Case for Staying on Standard Time

If we're going to pick one time and stick with it (and many experts think we should), most sleep scientists and health organizations advocate for permanent Standard Time, not permanent Daylight Saving Time.

Here's why: Standard Time is closer to our natural circadian rhythms. The sun being at its highest around noon matches up better with when our bodies expect it. Permanent Daylight Saving Time would mean very late sunrises in winter, especially in northern states. Kids would be going to school in the dark, which has safety implications and makes it harder to wake up.

The American Academy of Sleep Medicine, the American Academy of Sleep Medicine, and other major health organizations have published position statements supporting permanent Standard Time based on health evidence.

But People Like Evening Light!

This is true. Surveys often show people prefer having more light in the evening, which is what Daylight Saving Time provides. There's something nice about leaving work or school and still having daylight. Some studies suggest it reduces crime (more light = less crime) and increases physical activity.

The debate often comes down to priorities: do we optimize for health and circadian biology, or for social preferences and evening activities?

What's Happening Now?

The movement to end the clock changes has been gaining momentum. Multiple states have passed laws to adopt permanent Daylight Saving Time, but there's a catch: they need federal approval to do it. Under current law, states can opt out of DST and stay on Standard Time year-round (like Arizona and Hawaii do), but they can't stay on DST year-round without Congressional approval.

In 2022, the U.S. Senate unanimously passed the Sunshine Protection Act, which would have made Daylight Saving Time permanent nationwide. But the bill stalled in the House and never became law. The debate continues.

Meanwhile, most of the world doesn't do this. Only about a third of countries observe Daylight Saving Time, and several have recently abolished it, including most of Mexico, Turkey, and Russia.

The Bottom Line

Daylight Saving Time made more sense in a different era. The energy savings are minimal to nonexistent with modern technology. The health costs are real and measurable. And the twice-yearly disruption affects everything from heart attacks to car accidents to your ability to stay awake in first period.

Whether we should have permanent Standard Time, permanent Daylight Saving Time, or keep the status quo is still being debated. But the scientific evidence increasingly suggests that whatever we choose, we should stop changing the clocks twice a year.

So the next time you're groggily adjusting your watch and wondering why we do this, know that you're asking the right question. A lot of experts are wondering the same thing.

Sources

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Barnes, C. M., & Wagner, D. T. (2009). Changing to daylight saving time cuts into sleep and increases workplace injuries. Journal of Applied Psychology, 94(5), 1305-1317.

Kotchen, M. J., & Grant, L. E. (2011). Does daylight saving time save energy? Evidence from a natural experiment in Indiana. Review of Economics and Statistics, 93(4), 1172-1185.

Jiddou, M. R., et al. (2013). Incidence of myocardial infarction with shifts to and from daylight savings time. American Journal of Cardiology, 111(5), 631-635.

Janszky, I., & Ljung, R. (2008). Shifts to and from daylight saving time and incidence of myocardial infarction. New England Journal of Medicine, 359(18), 1966-1968.

Manfredini, R., et al. (2019). Daylight saving time and acute myocardial infarction: A meta-analysis. Journal of Clinical Medicine, 8(3), 404.

American Academy of Sleep Medicine. (2020). AASM position statement on daylight saving time. Journal of Clinical Sleep Medicine, 16(10), 1781-1782.

Fritz, J., et al. (2020). A chronobiological evaluation of the acute effects of daylight saving time on traffic accident risk. Current Biology, 30(4), 729-735.