Daylight Saving Time Makes Your Body Clock A Little Loopy. Here’s What To Know.

Our circadian rhythms, or body clocks, are in for a rude awakening as we “spring forward” an hour at the start of daylight saving time. Here’s what to know about how the time shift affects your health.

It’s that time of year again. On Sunday, March 12, most people in the US will “spring forward” — aka lose an hour of sleep as the clocks move ahead — and enter daylight saving time (DST). This means less sunlight in the morning and more of it in the evening, which you may consider a one-way ticket back into, or out of, the winter blues, depending on whether you’re a night owl or early bird.

While DST can be a sign that brighter, happier days are ahead, it’s not all sunshine and rainbows. This 60-minute shift, although seemingly small, can have a larger impact on your health besides making you an hour late for brunch on Sunday morning.

That’s because DST disrupts your circadian rhythm — the 24-hour body clock that’s governed by light — by forcing it to follow an unnatural schedule until November when the clocks switch back to standard time.

Circadian rhythms are a complex interaction of genes, enzymes, and hormones that control your daily fluctuations in mood, appetite, immune function, digestion, blood pressure, body temperature, and blood sugar, just to name a few.

Even if you pay no attention to the time, just about every tissue, organ, and cell in your body has an internal clock. So pushing those gears one hour forward can have consequences that could last for weeks or maybe even months.

One of the most obvious is sleep disruption, which is often to blame for the temporary rise in traffic accidents (along with driving in the dark), workplace mistakes, and injuries after the start of DST. The time change has also been linked to a risk, at least in the short term, of heart attack and stroke.

Meanwhile, DST doesn’t offer any obvious health benefits, Joseph Takahashi, an expert on biological clocks and chair of the neuroscience department at the University of Texas Southwestern Medical Center, told BuzzFeed News.

Of course, some people love DST because of the extra evening light that gives them a serotonin boost and more time to do outdoor activities after work or school. But not all US states and territories observe it. Hawaii and Arizona (excluding the Navajo Nation), do not, nor do the US territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the Virgin Islands. (About one-quarter of the world follows DST.)

If you live somewhere that makes the DST shift, here’s what to know about how it may affect your body clock and what it can mean for your health.

Why daylight saving time affects your body

DST’s hour shift disrupts our social clock, which dictates when we go to work, school, and hang out with friends. Our biological clocks, which follow the sun, can’t always keep up with the change. (Lots of clocks, I know).

The result is what scientists call “circadian misalignment,” or “social jetlag.” While you may be able to adapt to the change in a couple of days, some people struggle more, particularly those with sleep disorders, jobs with inconsistent hours, mental health problems, or other conditions such as autism.

But no matter who you are or what you do for a living, your body clock never really “adjusts,” Dr. Beth Malow, a professor of neurology and director of the sleep disorders division at Vanderbilt University Medical Center in Tennessee, told BuzzFeed News.

“I think you could say you adjust to the sleep loss in a few days, but from a circadian alignment standpoint, you're really off the whole period of time,” Malow said. “There's a mismatch between what's going on with the light and what's going on with our bodies. It kind of jars the system in a way that just moving time zones might not.”

What’s more, not all body clocks are the same; about 80% of people have a circadian rhythm that’s slower than 24 hours, whereas the remaining 20% have one that runs a bit faster, Takahashi said, which might explain why some people take longer to get used to the DST time change than others.

Then there are the trillions of microscopic clocks ticking inside every cell in your body.

“You can imagine that this mismatch in the synchronization of our clocks is not optimal and that just exacerbates many other aspects of our cellular function,” Takahashi said, “and perhaps maybe that's what tips the balance.”

Daylight saving time will likely disrupt your sleep

Experts agree the internal disarray caused by “springing forward” leaves the biggest mark on our sleep, according to the Society for Research on Biological Rhythms. It can often trigger short-term insomnia, daytime fatigue, irritability, lack of energy, and difficulty thinking straight.

A study of 55,000 people in Central Europe published in 2007 in the journal Current Biology found that on “free days” people reverted back to their biological clock instead of the social clock during DST. The researchers also followed a subgroup of 50 people for eight weeks around both time changes; the volunteers were either night owls, who preferred to stay up late and sleep in, or morning larks, who tended to get up and go to bed earlier.

The study found that while their sleep and peak activity levels quickly adjusted to the end of DST, they never really adapted to the change in spring, particularly if they were night owls.

The researchers say their findings suggest this “incomplete adjustment” isn’t just short-term, but can last for the entirety of DST.

Daylight saving time affects other aspects of our health, too

Heart attacks

DST is also associated with an increase in heart attack rates. For example, in one 2014 study published in the journal Open Heart, researchers looked at patients admitted to Michigan hospitals. They found that over three years, there was a 24% increase in the number of heart attacks on the Mondays after the start of DST compared with other Mondays of the year. On the Tuesdays following the return to standard time, there was a 21% drop in the number of heart attacks.

The researchers concluded that DST’s impact is limited to the timing of heart attacks and not the overall incidence; the abrupt changes in the sleep-wake cycle, as well as heightened stress related to starting a new work week, may trigger events in people who would have had them at some other point.


Stroke rates have also been found to jump after DST. In a study of hospitalized patients in Finland, stroke rates were 8% higher in the two days after the start of DST compared with rates in the two weeks before and after. The 2016 study was published in the journal Sleep Medicine.

Workplace mistakes and injuries

A 2020 study published in the Journal of General Internal Medicine found that “human errors” among healthcare workers in the Mayo Clinic Health System increased about 19% in the week after the springtime change compared to the week prior. These errors included giving people incorrect medications or dosages, mislabeling laboratory samples, and making mistakes during surgery. There was no increase in errors made around the end of DST in the fall.

A 2009 study of mine workers from a National Institute for Occupational Safety and Health database found workers experience more injuries, and more severe injuries, the Mondays right after DST compared to other days.

Car accidents

There’s also some evidence that suggests a link between DST and increased traffic accidents, which could be explained by tired drivers traveling during darker mornings. A study looking at 21 years of data on car accidents in the US found that about an additional 28 car accident-related fatalities occurred during the workweek after the DST transition compared to any other week. The findings were published in 2020 in the journal Current Biology.

Who’s most affected by daylight saving time?

Anyone can be thrown off when the time changes in the middle of the night, but some people are more affected than others.

Teenagers, for example, face some of the greatest risks of sleep deprivation following the DST change because they already deal with chronic sleep issues during the school week, according to the American Academy of Sleep Medicine.

There’s a biological explanation, too, Malow of Vanderbilt said. Teens release their natural melatonin levels an average of two hours later than adults because their body clocks shift to a later period during puberty. So when DST comes around, their already altered sleep becomes even more disrupted, which is only made worse with their busy social lives, early school schedules, and any jobs they may have.

Shift workers who work unusual hours are also more likely to struggle with DST. Some members of this group already have shift work disorder (a type of circadian rhythm disorder), which causes them to sleep up to four hours less than the average worker and have poor sleep quality overall, the AASM says.

People who live on the US West Coast, where the difference in social clocks and body clocks is greater than on the East Coast, may also feel the shift more.

Changes in mental health after the switch to DST may be more noticeable or serious in people with seasonal affective disorder — a type of depression related to seasonal changes and lack of sunlight — who are sensitive to disturbances in their body clocks.

Malow said people with certain conditions that make them vulnerable to changes in their daily patterns, like autism and bipolar disorder, are more likely to experience severe disruptions in their mood and functioning following the DST shift.

How to ensure the smoothest transition into daylight saving time

If you haven’t guessed already, you’ll definitely want to prioritize sleep around the start of DST. Malow suggests going to bed a little earlier (about 15 to 20 minutes) two to three days before the switch to DST — that way you’ll be extra rested when that hour is taken from you later on.

And try not to sleep in on the day of the switch, Malow said. “You want to try to wake up fairly early. Not crazy early, but 7 or 8 a.m., and get exposed to the bright light because that light in the morning will help you reset yourself.”

Here are some other ways you can minimize DST’s impact on your sleep and overall health:

  • Start your daily routines, such as eating dinner, that serve as time cues for your body in the days before the DST switch a bit earlier
  • Set your clocks ahead one hour Saturday evening so you start adjusting before the time actually changes overnight — then go to sleep at your normal bedtime
  • Go to bed at your usual time on Sunday night to be well rested for the workweek
  • Ensure healthy sleep habits: Get seven to nine hours of rest a night, keep your bedroom dark and cool, and avoid caffeine or alcohol before bed

Is daylight saving time here to stay?

You either love it or hate it, but DST is here to stay — at least for now.

In an effort to conserve fuel, the US first adopted DST in 1918 after Europe tried it during World War I. However, the move was unpopular and it was reversed after the war; people didn’t like waking up in the dark, especially in the winter.

DST was then standardized in the US in 1966, with the same energy conservation idea in mind (policymakers assumed people wouldn’t need to use energy in the evening because of extra sunlight). Even though that didn’t turn out to be the case, DST persevered, with some modifications along the way.

In the last few years, nearly 20 states have initiated the legal process to adopt yearlong DST, with Florida being the first to enact legislation for permanent DST (Congress has yet to approve the bill).

Meanwhile, doctors and scientists are itching on the sidelines. In 2020, the AASM published a position statement in the Journal of Clinical Sleep Medicine that called for the elimination of “seasonal time changes in favor of a national, fixed, year-round time,” stating that evidence shows standard time “aligns best with human circadian biology and provides distinct benefits for public health and safety.”

The statement was endorsed by over 20 organizations, including the American Academy of Cardiovascular Sleep Medicine, Society for Research on Biological Rhythms, American Academy of Dental Sleep Medicine, National PTA, and National Safety Council.

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