When you set your clock forward an hour every spring for daylight saving time (DST), it doesn’t just make you feel tired, experts say. A growing amount of research indicates that it also affects your body in other surprising and negative ways.
Losing an hour may not seem like a big deal, but it “really can have a significant impact on our overall health and well-being,” says Melissa Lipford, M.D., a neurologist and sleep specialist at the Mayo Clinic.
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.
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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.
A 2019 survey conducted by the American Academy of Sleep Medicine found that 55 percent of adults feel extremely or somewhat tired after the time change.
Even if you don’t feel tired, daylight saving time throws your body’s internal clock out of whack, which can affect you in ways you don’t realize, says Jocelyn Cheng, M.D., a neurologist and sleep medicine specialist who is a member of the Public Safety Committee for the American Academy of Sleep Medicine.
“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.”
Here are some ways DST 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. Another found the risk of stroke is 8 percent higher on the two days following the time change.
In addition, the number of people hospitalized with AFib — 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.
Scientists aren’t sure why daylight saving time impacts your heart and blood vessels, but it’s likely related to the disruption of the body’s circadian rhythm, says American Heart Association President Donald Lloyd-Jones, M.D., chair of the department of preventive medicine at Northwestern University’s Feinberg School of Medicine.
“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. Impaired decision-making
Scientists have long known that lack of sleep can affect your ability to think and make decisions. Studies also show 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., assistant professor with the Center for Circadian and Sleep Medicine at Northwestern University’s Feinberg School of Medicine.
“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 explains. “The less sleep you get, the more likely you are to give into 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 author’s said the spike was most likely explained by “circadian misalignment and sleep deprivation.”
3. Difficulty with memory and focus
Lack of sleep negatively impacts memory, attention span and focus, research shows.
Expect to be more easily distracted and less productive the day after you set your clock forward. 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 time change.
“When we sleep, a lot of critical tasks happen in our brain,” Lipford explains. “We need good deep sleep so the next day we can multitask, learn new tasks and pay attention.”
4. Appetite changes and cravings
You may feel hungrier than normal the week after the time change, experts say.
That’s partly because you’re eating your meals an hour later than you’re used to. 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 pains 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.
5. 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; 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 time change, head to bed about 15 or 20 minutes earlier 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 wakeup 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.
- Consider a small dose of melatonin. If you still find it difficult to fall asleep, consider taking a small dose of melatonin — half a milligram to a milligram — about 30 minutes before bedtime, Abbott suggests.
Michelle Crouch is a contributing writer who has covered health and personal finance for some of the nation’s top consumer publications. Her work has appeared in Reader’s Digest, Real Simple, Prevention, The Washington Post and The New York Times.