Why the Fall Time Change Throws Off Your Body Clock—and How to Reset ItCreated with Avocado

Turning back the clocks and gaining an extra hour of sleep every fall sounds like, well, a dream—until you realize the time change can leave you feeling off for days.

While it may seem like the kind of minor sleep glitch easily remedied with a strong cup of coffee, the end of daylight saving time can wreak havoc on our systems. That's because “the one-hour shift sets off a much bigger chain reaction than most people realize, one that touches hormones, hunger, mood, and more,” says Sarah Bjork, MD, a sleep medicine specialist at Montefiore Einstein.

The Science Behind Falling Back

When the clocks change, your internal clock, or circadian rhythm, is suddenly out of sync with the time on your phone. Light is one of the main signals that sets your body clock and tells you when to feel alert or sleepy, so even a one-hour shift in morning and evening light can have an outsized effect.

Your hormones are also programmed to spike at specific times of day, which is another reason that one-hour shift can feel so pronounced. “Hormones like a routine, and when they’re thrown off, they behave like very bad actors,” says Vanessa Coppola, DNP, FNP-BC, MSCP, a board-certified nurse practitioner and integrative specialist.

For example, melatonin, the hormone that tells your body it’s time to sleep, is generally released when it's dark out, so when the clock changes, your body's natural sleep signals may not line up with your new bedtime. Cortisol, often described as our stress hormone, also follows an essential daily rhythm. “Levels generally rise toward morning and decline throughout the day, reaching low levels around the early part of the usual sleep period. Sleep loss can affect this pattern,” she explains. When sleep is disrupted, the result is a frustrating combination that Coppola often hears described as “‘I am exhausted, but I cannot settle down.’”

Changes in sleep and circadian timing can affect ghrelin and leptin, the hormones that regulate hunger, leaving you hungry (and hangry) at times you wouldn’t expect. “And cravings can become insatiable for foods like carbs that help keep us energized,” Coppola says.

Why Some People Feel the Time Change More Than Others

For most healthy adults, it doesn’t take too long to adjust to the time change: “On average it will take a week or two,” Bjork says. And many people find the fall time change easier than the spring shift. “When the sun sets a bit earlier and it’s cozier in the evenings, that helps our body relax and reset,” she says.

But not everyone adjusts at the same pace. It depends on your sleep chronotype—whether you’re naturally an early bird or a night owl. “For people who are naturally early risers, falling back works well because there’s more light in the morning when they’re apt to be up anyway,” Bjork says. For night owls, that earlier morning light may arrive before their bodies are ready to wake up.

Another factor: “Parents of young children and pets may feel it more, since infants, toddlers, and animals don’t understand the social cues as adults do, so they don’t quite get what we’ve forced on them,” Bjork says. Shift workers are also especially vulnerable: “They generally have problems sleeping, but their chronic misalignment can be amplified during this time.”

The Reset Protocol

Bjork’s best advice starts before the clocks even change. “Going into the time change, move everything 15 minutes in the direction the time is changing,” she says. In fall, that means inching back your regularly scheduled activities like bedtime, mealtime, and exercise, by 15-minute increments roughly every other day for the week leading up to the end of daylight saving time. Then, when that hour change comes, you’ll have had enough time to adjust.

Once the time change hits, morning light is your single most effective weapon for staving off sleepiness, Bjork says. “When you wake up, expose yourself to bright light. It doesn’t even need to be the sun; it may just mean turning on the lights.” In the evenings, Bjork recommends the opposite approach, ending the day with dim or softer light.

What Backfires

What won’t help your body adjust is a double shot of espresso. “Too much caffeine can cause rebound fatigue or tiredness in the afternoon that undoes everything you’ve worked for if you’ve been prepping for the time change,” Bjork says. Her recommendation is to stop coffee intake anywhere from 2 to 4 p.m.

And while a melatonin supplement can help you fall and stay asleep, it only works  if  timed properly: 90 minutes to two hours before you want to fall asleep, Bjork says. Taken outside this timeframe, you may not get the surge of sleepiness when you need it most.

Counterintuitively, trying to “sleep off” the time change can also work against you. “There is such a thing as too much sleep,” Bjork says. “If we’re oversleeping, it can prohibit us from being active during the day and getting enough light, both of which can make us groggy and fatigued.”

Beyond This One Weekend

The disruption doesn’t necessarily end once your body catches up to the new time. “Lack of light may continue to influence the body throughout the fall and winter, when it gets darker earlier and, in colder climates, people aren’t as active,” Bjork says. So her advice holds for the entire darker stretch ahead, not just the first week: Stay consistent with sleep, get morning light whenever possible, keep moving during the day, and treat caffeine and melatonin timing as tools to be used sparingly—and intentionally.