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Medically reviewed by: Alison Kole, MD, MPH, FAASM
For most of the United States, a major switch happens in early November. We move from daylight saving time back to standard time. It's a change we expect each year, but our bodies still feel the real impact.
What is the difference between daylight saving time and standard time?
Daylight saving time was first tested in Germany and Austria in 1916 to conserve fuel during World War I, and the U.S. followed in 1918. Then in 1966, Congress passed the Uniform Time Act, which standardized biannual shifts from daylight saving time to standard time across the United States. What was originally created to save on energy has now started to cost us our sleep and overall health.
What actually changes when we switch? It may seem like we get more sunlight during the day with daylight saving time, but that's false. We are just trading one hour of sunlight in the morning for one hour of sunlight in the evening. And that trade matters more than you may think.
Our bodies have a built-in clock, called our circadian rhythm, that runs slightly more than a day, about 24.2 hours. Light is what resets our circadian rhythm each day. Morning light tells our body it’s time to wake up and start the day. Evening light sends the opposite signal. With daylight saving time, we get more of that late light, so our body clock runs later. That can make it harder to fall asleep at night and harder to wake up in the morning.
For most of us, the day starts early. If we were to keep daylight saving time all year, in the peak of winter, the sun wouldn't rise until after 9 a.m. in some cities, leaving people to commute and start their days in the dark.
Why do sleep experts want permanent standard time?
Because standard time gives us more morning light, it helps keep our circadian rhythm steady. That's why the American Academy of Sleep Medicine recommends that the U.S. stop changing clocks and stay on standard time all year.
In a 2025 Stanford modeling study, researchers compared three options: switching twice a year, staying on daylight saving time, and staying on standard time. In this study, standard time came out on top. The researchers estimated it could mean about 300,000 fewer strokes each year and about 2.6 million fewer people living with obesity.
What does the time change mean if you have sleep apnea?
If you have sleep apnea, the time change can hit a little harder. Sleep apnea causes your breathing to stop and start throughout the night. Each pause can briefly wake your brain, even if you don't remember it, so your sleep is already broken up before the clock ever changes.
Untreated sleep apnea is linked to heart disease, stroke, and drowsy driving. Any disruption to your sleep schedule, including the clock change to daylight saving time, adds strain to a system that’s already under pressure. That's why using your CPAP or oral appliance every night matters so much, especially in the days around the switch.
How can you adjust to the time change?
The good news is that a few small changes can make the switch easier on your body.
- Soak up the morning light. Get outside within an hour of waking up, even on cloudy days. Morning light helps reset your circadian rhythm, and it can give your mood a lift as the evenings get darker.
- Wind down in dim light. Lower the lights and put screens away about an hour before bed.
- Keep a steady wake-up time. Try to get up at the same time every day, even on weekends.
Not sure if it's the time change or sleep apnea that's making you feel off? Ognomy Sleep can help evaluate your symptoms, all from the comfort of your home. Schedule a virtual visit with one of our sleep medicine clinicians today to get to the bottom of your symptoms.
Frequently asked questions
Which is better for sleep, standard time or daylight saving time?
Most sleep experts say standard time. It gives you more morning light, which keeps your circadian rhythm on track.
Will the U.S. stop changing clocks?
Earlier this year, the House passed a bill for year-round daylight saving time—the Sunshine Protection Act—pushing to end the disruption of shifting time twice a year. However, it has not become law. Instead of adopting this hazardous framework, the Senate should support the newly established Sunshine for Our Kids Act, which would end clock change while supporting circadian health by establishing permanent Standard Time as the national default.
