Oct. 29, 2025 — Our internal body clock influences nearly every aspect of our health, including hormones, metabolism, immune function, and brain activity. And it doesn’t like being reset.
Recent research reveals how the twice-yearly switch to and from daylight saving time disrupts that delicate rhythm in ways that affect our sleep, mood, and health.
How should you handle the upcoming “fall back” to standard time next Sunday, Nov. 2? To find out, we read the studies and asked the experts.
Is Gaining an Hour Really Easier Than Losing One?
It usually feels that way — but that doesn’t mean “falling back” won’t disrupt your internal clock.
Research shows that morning light advances the body clock (so you wake and sleep earlier), while evening light delays it, making you stay up later. “Spring forward” — when we set the clocks ahead an hour on the second Sunday in March — removes morning light and extends evening light, nudging most people’s rhythms later just when they need to be earlier. That’s why the time change feels especially rough in spring.
The fall change adds morning light and reduces evening light, so it can feel like a freebie. “You can ‘just stay awake an hour later than usual’ and let the extra morning light help you adapt,” said Jamie M. Zeitzer, PhD, professor of psychiatry and co-director of Stanford’s Center for Sleep & Circadian Sciences.
The risk: Your body clock can still drift later — and start running behind the new time — if you lean into brighter evenings with artificial light, said Zeitzer. Evening light is a strong “delay” signal, he said, and home lighting can be bright enough to suppress melatonin and push circadian timing later, especially if daytime light exposure was limited. That means you could have a harder time falling (or staying) asleep and wake up groggier.
How Does a Time Change Affect Your Health?
Research is clearest on fatigue and performance, particularly in those who are already sleep-deprived, said Michael A. Grandner, PhD, director of the Sleep and Health Research Program at the University of Arizona.
Driving-simulator studies show poorer vehicle control and increased eyelid closure, particularly after springing forward, with some deficits persisting beyond the first week, often without drivers recognizing the decline.
In the fall, the later shift is tied to downsides: a rise in depressive episodes, plus broader links between “social jetlag” — a mismatch between your body clock and your work, school, or social schedule — and poorer sleep, higher metabolic risks (including obesity, diabetes, and cardiometabolic disease), and worse mental health.
On heart attacks, the latest evidence is mixed. A 2024 meta-analysis points to a small post-spring bump, while a large 2025 U.S. registry analysis found no significant spike in heart attacks around daylight saving time weeks. “Your blood pressure and heart rate rise in the morning as you wake up, and a sudden spike upon awakening might, in extreme cases, be enough to cause a cardiac event for people who are at high risk,” said Grandner. In other words, the physiology makes a rare event plausible in people who are already vulnerable.
How Should I Handle the Fall Time Change?
Experts recommend a few options.
Keep your body clock steady. Stay on the same solar schedule by going to bed and waking slightly earlier by the new clock, Grandner suggested. Prioritize strong morning light and movement.
If you slept from 11 p.m. to 7 a.m. before the change, switch to 10 p.m. to 6 a.m. by the new clock. That way, you’ll get the same or more morning light and less evening light, helping your body stay on track.
Ease into the new time. If you prefer to keep your usual clock bedtime and wake time — 11 p.m. to 7 a.m. — that’s fine too. Just shift gradually, moving bedtime and wake time 15 to 20 minutes later each night. Continue getting bright light early in the day.
Bank a bit of sleep, once. If you’re short on sleep, it’s OK to use the extra hour for rest, Grandner said. If you normally wake at 7 a.m., then wake on Sunday morning at 7 a.m. new time (which feels like 8 a.m. old time). On Monday, resume your usual schedule — 6 a.m. by the new clock — and get outside soon after waking.
What Should I Do After the Time Change?
Focus on your evenings. Keep lights low for a few hours before bed to help your internal clock shift to the new time faster. Zeitzer points to modeling of real-world routines indicating that evening light exposure is the biggest factor in how quickly people readjust.
Zeitzer noted that while intensity matters most for circadian effects, warmer-tone bulbs can serve as a behavioral cue to wind down — your brain notices color shifts more than modest dimming. Think “soft white” bulbs around 2700K (often labeled Soft/Warm White) for evenings, or go extra-warm at 2200K, which is marketed as “amber,” “vintage Edison,” or “candlelight.”
During the day, get outside. Zeitzer said about 30 minutes outdoors, even on overcast days, makes typical evening home lighting effectively negligible to your body clock. The circadian system weighs evening light against the daylight you received earlier that same day, so stronger daytime exposure makes evening light matter less.
Anchor this routine with earlier meals during the changeover — another cue that helps your body clock settle more quickly.
What Should I Not Do?
Don’t lean too much on caffeine, and keep a wide buffer between your morning coffee and bedtime, particularly in the first three to five days after the change, when your body clock is most sensitive. This applies to both fall back and spring forward; modeling and empirical work suggests a one-hour change typically takes several days (and sometimes longer) to settle.
A randomized crossover trial, published in Sleep in 2025, found 400 milligrams of caffeine (about four cups of coffee) within 12 hours of bedtime can still delay sleep onset, fragment sleep, and alter sleep stages — even if you feel fine. So keep your last strong caffeine in the late morning, especially that first week.
Short naps are OK if you need a boost, but limit them to 20 to 30 minutes, early in the day. Skip late-day “rescue” naps, which can make it harder for your clock to settle on the new schedule.
