Here’s how daylight saving time can hurt your heart health

Many Americans curse the clock for their resulting grogginess when the time jumps forward for daylight saving time, but it’s not just energy that takes a hit during the time change. Sleep and circadian rhythm disruptions take a toll on heart health too.

“When we sleep, our heart is able to rest and go into a restoration mode where it can restore itself, and our entire cardiovascular system can rest and repair,” says Kelsie Full, behavioral epidemiologist at Vanderbilt University Medical Center. “So if we're not sleeping well and our sleep is disrupted, we see impairment or dysregulation of that cardiovascular system.”

The cardiovascular system, like much of the rest of the body, operates around our circadian rhythm—the 24-hour clock that regulates biological processes. But when the time changes in the spring, our waking hours become misaligned with this system governed by cues of natural light. 

(​Why daylight saving time exists—at least for now.)

An hour may be a relatively short time shift, but research shows very real negative heart health consequences associated with daylight saving time and the resulting misalignment with our circadian rhythm. Here’s how the time change can affect heart health in the days after and in the sunnier months that follow.

How daylight saving affects your circadian rhythms 

From March 8 to November 1, clocks will return to standard time in the United States as daylight saving time maximizes sunlight during waking hours in the spring and summer. About a third of other countries observe the change as well, although timing varies.

Since 1966 (minus a small blip in the ’70s), U.S. residents have followed this pattern, but research suggests that this change, specifically the jump in the spring, can spur a host of health problems, among them, heart issues.  

(America once made daylight saving time permanent. Here’s what went wrong.)

It’s hard not to focus on the short-term effects of sleep loss, especially when your alarm goes off on the second Monday in March. And although occasional small studies pop up showing bumps in heart attack hospital admissions the day after daylight saving time begins in the spring, much larger study published in 2025 refutes that idea. Examining records of nearly 170,000 patients, researchers found no significant increase in heart attack cases after daylight saving time began.

Instead it’s the months that follow the change that’s the biggest cause for concern. Although we may adjust to the initial feelings of tiredness over the course of two to five days, says Susan Redline—a sleep medicine specialist at Harvard Medical School—daylight saving doesn’t begin and end in one day. 

“Once we make that one-hour change, then our bodies are in chronic misalignment where our physiological processes that are occurring in our body are not aligned with the environmental cues, which include natural sunlight,” Full says. “So, we're kind of staying in that phase of misalignment chronically for eight months.”

Losing an hour of sleep may seem insignificant, but an overall lack of sleep forces your heart to work harder by increasing stress hormones, blood pressure, and inflammation, which raises the risk of heart disease, heart attack, and stroke. In one study, sleeping fewer than six hours a night was associated with a 20 percent increase in heart attack risk.

One missed hour likely isn’t enough to cause a heart attack, but these hours add up. “If you're doing that over a period of time, not maintaining good sleep hygiene, that can be associated with increased body weight, increased rates of obstructive sleep apnea, increased blood pressure, and then can contribute to an increased risk of cardiovascular conditions,” says Rymer. A February 2026 study found that shorter sleep duration was associated with atrial fibrillation, an irregular heartbeat that can lead to blood clots, among individuals in their 50s.

Amount of sleep is important (doctors recommend seven hours a night at a minimum), but consistency of sleep is key. One study, led by Susan Redline and a team of sleep researchers at Harvard Medical School, found that participants with irregular sleep schedules had more than double the risk of developing cardiovascular disease, regardless of sleep duration and prior cardiovascular risk factors. 

In studies of adults 35 and older, “people whose night-to-night variation and when they go to bed may vary by one hour chronically are at about a 30 to 50 percent increased risk of developing heart disease and various metabolic problems of diabetes,” Redline says. 

This goes against our circadian rhythm, which regulates the timing of processes across our bodies, including in our hearts. Effects of circadian misalignment often mirror those of poor sleep quality, duration, and consistency, which, when occurring together like they frequently do in daylight saving time, can compound the effects on our cardiovascular system. 

Disruption of this natural sleep and waking cycle affects the ability to regulate blood pressure and is associated with an increase in cardiovascular disease—the leading cause of death in the United States. We know that long-term circadian rhythm disruption can have real consequences: studies show that night shift workers have a 17 percent higher rate of cardiovascular disease.

These effects may not be immediately obvious, but consistent, quality, and circadian-aligned sleep is crucial to heart health, whether or not it becomes apparent in a day or years later. 

“A lot of Americans struggle with their sleep,” Full says. “It's normal to have to have  some problems with your sleep, and it's also a great idea if you notice that, whether it's daylight savings or throughout that eight month period, if you really struggle with your sleep, there are sleep clinicians and sleep providers that can help you, and it's a great idea to talk to them.”