6 Surprising Ways Your Body Reacts to Daylight Saving Time

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.

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, sleep medicine specialist and vice chair 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.”

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. 

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 more 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. 

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

1. May increase risk of heart attack and stroke 

Experts have long said 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 spring and the fall time changes.​

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.  

​But researchers at the Mayo Clinic are questioning the idea that daylight saving time increases heart attacks and strokes. In a new study looking at more than 36 million adults age 18 and over across the United States, researchers analyzed heart attacks and strokes at a large insurance databank, in the week after the spring and fall daylight saving transitions.

Benjamin Satterfield, M.D., assistant professor of medicine at the Mayo Clinic, said previous small studies on an increase in heart risks from daylight savings prompted researchers to look at the data from a large group of people in the United States.

"These cardiovascular events are common health conditions, so this led to the question of whether this is more than would be expected if this had not followed the daylight saving time transition," said Satterfield, lead author of the study, which was published in the Mayo Clinic Proceedings: Innovations, Quality & Outcomes.

​He told AARP that after reviewing the data they concluded that “the very small increase in cardiovascular events — heart attacks, strokes, cardiac arrests, etc. —we observed after daylight saving time change on a national level is not likely to have a meaningful, clinical impact.” 

Dallas-Fort Worth area cardiologist John Osborne, M.D., said the science isn’t settled on whether the time changes in the spring and fall are dangerous for heart health. “A number of other studies have seen both clinically and significant increases in cardiovascular events during DST transitions, so I don’t think the debate is in any way settled,” says Osborne, an American Heart Association volunteer expert. 

Clearly, for heart health, sleep and sleep hygiene are important and should continue to be addressed to help reduce risks. “To do otherwise would mean that we are dangerously ‘asleep at the wheel,’” Osborne told AARP.

Scientists aren’t sure why daylight saving time might affect 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.”