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6 Surprising Ways Your Body Reacts to Daylight Saving Time

The twice-yearly time reset can negatively affect your mood, and may increase the risk of a heart attack or stroke

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You may look forward to the extra hour when you set your clock back for the end of daylight saving time in the fall. But a growing amount of research indicates that shifting our clocks twice a year affects our bodies in some surprising and negative ways.

Daylight saving time throws your body’s internal clock out of whack, which can negatively affect your health in ways you don’t realize, says Jocelyn Cheng, M.D., a neurologist and sleep medicine specialist who is the vice chair of the Public Safety Committee for the American Academy of Sleep Medicine. 

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 “Light is the most powerful regulator of our circadian rhythm. When we change the light exposure we get in the morning and at night, it throws that off,” Cheng says. “There are adverse health consequences and real-life consequences as a result of that.”

Daylight saving time has been around in the United States since 1918, when it was thought to save energy during World War I. In recent years, increasing concerns about health effects have prompted at least 40 states to propose legislation to eliminate the twice-yearly time changes.

A 2020 survey conducted by the American Academy of Sleep Medicine found that 63 percent of adults would prefer to eliminate seasonal time changes. 

For most people, setting the clock ahead in the spring is the most dreaded change. The average person gets about 40 minutes less sleep on the Monday after “springing forward” for daylight saving time, according to the Sleep Foundation . And experts say it’s not unusual for a person’s sleep to be disrupted for days or weeks afterward. 

In the fall, we talk about “gaining” an hour of sleep, but most people still experience a net loss of sleep time that night and in the days following, because they wake up earlier, have more trouble falling asleep or wake up during the night, according to a review published in the journal Sleep Medicine Reviews.

Early risers tend to have the most trouble adjusting, the study said.

Here are some ways the disruptions from daylight saving time can affect your body.

1. Higher risk of heart attack and stroke

Daylight saving time takes a toll on your heart. One study found a 24 percent increase in heart attacks on the Monday after daylight saving time starts.

In addition, the number of people hospitalized with atrial fibrillation, or A-fib — the most common type of irregular heartbeat — surges in the days following the spring time change, according to a 2020 analysis of 6,089 patient admissions at Montefiore Medical Center in New York.  

While the spring time change is most strongly linked to cardiovascular problems, some research also points to increased risk after clocks roll back in the fall. For example, a 2019 meta-analysis of seven studies published in the Journal of Clinical Medicine found a higher risk of heart attacks in the two weeks after both the spring and fall transitions.

Another study found the risk of stroke  is 8 percent higher on the two days following the spring and the fall time change.

Scientists aren’t sure why daylight saving time affects your heart and blood vessels, but it’s likely related to the disruption of the body’s circadian rhythm, says Donald Lloyd-Jones, M.D., chair of the Department of Preventive Medicine at Northwestern University’s Feinberg School of Medicine and past president of the American Heart Association. 

“We get established in these patterns and the body knows what to expect,” he says. “When those patterns get disrupted, you tend to see differences in stress hormone levels and differences in blood pressure levels. Both of those things can be triggers for heart attacks and strokes that might not otherwise have happened.”

2. Low mood and depression

The early onset of darkness and shorter days after the fall rollback can leave you feeling lethargic and out of sorts. When you don’t get enough exposure to sunlight, your body doesn’t make as much serotonin, the brain chemical responsible for lowering anxiety and boosting mood. You also get less vitamin D, and vitamin D deficiency has been linked to depression and fatigue.

One study found that the fall clock change was associated with an 11 percent increase in depressive episodes.


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3. Impaired decision-making

Scientists have long known that lack of sleep can affect your ability to think and make decisions. Studies also show that people who don’t get enough shut-eye are more likely to take risks and make mistakes.

That may explain why there’s a spike in medical errors, workplace injuries and car wrecks after people reset their clocks in the spring, says Sabra Abbott, M.D., associate professor at Northwestern University’s Feinberg School of Medicine and director of the Northwestern Circadian Medicine Clinic.

“In general, sleep deprivation removes the frontal lobe functions in our body — that’s the part of the brain that keeps us in check and from doing things we shouldn’t do,” Abbott says. “The less sleep you get, the more likely you are to give in to impulses, and the less likely you are to make good choices.”

A 2020 study that examined vehicle accident data over a 10-year period revealed a 6 percent increase in fatal car crashes in the week after people reset their clocks in the spring. Because there was no similar increase in the fall when people gain an hour of sleep, the study authors said the spike was most likely explained by “circadian misalignment and sleep deprivation.”  

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4. Difficulty with memory and focus

Lack of sleep negatively affects memory, attention span and focus, research shows.

Expect to be more easily distracted and less productive for a few days after a daylight savings transition. One study published in the Journal of Applied Psychology revealed a sharp increase in “cyberloafing” — using the internet for personal use rather than working — on the Monday after the spring time change.

“When we sleep, a lot of critical tasks happen in our brain,” says Melissa Lipford, M.D., a neurologist and sleep specialist at the Mayo Clinic. “We need good deep sleep so the next day we can multitask, learn new tasks and pay attention.”

5. Appetite changes and cravings

You may feel hungrier than normal the week after the time change, making you more likely to overeat, experts say.

In the fall, that’s partly because you’ll start to feel hungry an hour before your normal meal time. But it’s also because of fluctuating hormone levels in your brain. Even a small sleep deficit increases the hormone ghrelin — which makes you hungry — and suppresses the hormone leptin, which helps you feel satisfied after you eat.

When those hunger pangs hit, you’ll probably find yourself reaching for pizza, doughnuts or other foods that are high in fat or sugar. Why? Because science shows that “when you’re sleep deprived, you tend to make fewer healthy choices,” Lipford says.

6. Increased irritation

You already know that when you’re tired, your mood is affected. Research indicates that it’s harder to regulate your emotions when you haven’t gotten a good night’s sleep. You feel irritable, impatient and more likely to snap at loved ones.

Even judges, who are supposed to be impartial, may be moodier in the days after daylight saving time begins; one study found that they dole out harsher sentences immediately after the shift.

Help Your Body Adjust to Daylight Saving Time

  • Start adjusting in advance. In the days leading up to the fall time change, head to bed about 15 or 20 minutes later each night. Adjusting gradually helps the time change be less of a shock to your system.
  • Expose yourself to morning light. As soon as you wake up, try to get outside. The morning light will send a strong wake-up signal to your brain and help reset your internal clock. If you can’t get outside, at least try to get to a window.
  • Cut out coffee by 2 p.m. You may be tempted to down some extra caffeine to get you through the midday slump, but caffeine can linger in your system and hurt your ability to fall asleep.
  • Practice good sleep hygiene. To stimulate sleep after the time change, make sure your bedroom is dark, quiet and cool. Avoid alcohol and electronic devices before bed, and adopt a calming bedtime routine.

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