Daylight saving time starts Sunday; how it could affect your health

Most of America “springs forward” Sunday for daylight saving time. Losing that hour of sleep can do more than leave you tired and cranky the next day; it also could harm your health.

Darker mornings and more evening light knock your body clock out of whack — which means daylight saving time can usher in sleep trouble for weeks or longer. Studies have even found an uptick in heart attacks and strokes right after the March time change.

There are ways to ease the adjustment, including getting more sunshine to help reset your circadian rhythm for healthful sleep.

When does daylight saving time start?

Daylight saving time begins Sunday at 2 a.m., an hour of sleep vanishing in most of the U.S. The ritual will reverse on Nov. 1 when clocks “fall back” as daylight saving time ends.

Hawaii and most of Arizona don’t make the spring switch, sticking to standard time year-round — along with Puerto Rico, American Samoa, Guam and the U.S. Virgin Islands. Worldwide, dozens of countries also observe daylight saving time, starting and ending at different dates.

Some people try to prepare for daylight saving time by going to bed a little earlier two or three nights ahead. While getting back on schedule after an hour's change may not be that difficult for some people, it's an added challenge for the third of U.S. adults who already don't get the recommended seven hours of nightly shuteye.

What happens to your brain when it's lighter later?

The brain has a master clock that is set by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when we become sleepy and when we’re more alert. The patterns change with age, one reason that early-to-rise youngsters evolve into hard-to-wake teens.

Morning light resets the rhythm. By evening, levels of a hormone called melatonin begin to surge, triggering drowsiness. Too much light in the evening — that extra hour from daylight saving time — delays that surge and the cycle gets out of sync.

Sleep deprivation is linked to heart disease, cognitive decline, obesity and numerous other problems. And that circadian clock affects more than sleep, also influencing things like heart rate, blood pressure, stress hormones and metabolism.

How does the time change affect your health?

Fatal car crashes temporarily jump the first few days after the spring time change, according to a study of U.S. traffic fatalities. The risk was highest in the morning, and researchers attributed it to sleep deprivation.

Then there’s the cardiac connection. The American Heart Association points to studies that suggest an uptick in heart attacks on the Monday after daylight saving time begins, and in strokes for two days afterward.

Doctors already know that heart attacks, especially severe ones, are a bit more common on Mondays generally — and in the morning, when blood is more clot-prone.

Researchers don't know why the time change would add to that Monday connection but it's possible the abrupt circadian disruption exacerbates factors such as high blood pressure in people already at risk.

How to adjust to daylight saving time

Go outside for early morning sunshine that first week of daylight saving time, which can help reset your body's internal clock. Moving up daily routines, like dinner time or when you exercise, also may help cue your body to start adapting, sleep experts advise.

Afternoon naps and caffeine as well as evening light from phones and other electronic devices can make adjusting to an earlier bedtime even harder.

Will the U.S. ever eliminate the time change?

Every year there's talk about ending the time change. Before starting his second term, President Donald Trump promised to eliminate daylight saving time. A bipartisan bill named the Sunshine Protection Act to make daylight saving time permanent has repeatedly stalled in Congress.

But that's the opposite of what some health groups recommend. The American Medical Association and American Academy of Sleep Medicine agree it's time to do away with time switches but say sticking with standard time year-round aligns better with the sun — and human biology — for more consistent sleep.

Even though polls show most people dislike the system that has most Americans changing clocks twice a year, the political moves necessary to change the system haven't succeeded because opinions on the issue and its potential impacts are sharply divided.

Want to make daylight saving time permanent? That would mean the sun rises around 9 a.m. in Detroit for a while during the winter. Prefer staying on standard time year round? That would mean the sun would be up at 4:11 a.m. in Seattle in June.

“There’s no law we can pass to move the sun to our will,” said Jay Pea, the president of Save Standard Time, an organization devoted to switching to standard time for good.

Here's a look at the debate.

Imposing a clock on a rotating planet causes a lot of headaches

Genie Lauren spends her winters in New York City keeping an eye on the sunrise and sunset “white-knuckling it” until the sun is up late enough for her to feel like doing anything outside her apartment after work — even going to the movies.

“The majority of the year we’re in daylight savings time,” said the 41-year-old health care worker. “What are we doing this for?”

The U.S. has tinkered with the clock intermittently since railroads standardized the time zones in 1883. So has a lot of the world. About 140 countries have had daylight saving time at some point; about half that many do now.

About 1 in 10 U.S. adults favor the current system of changing the clocks, according to an AP-NORC poll conducted last year. About half oppose that system, and some 4 in 10 didn’t have an opinion. If they had to choose, most Americans say they would prefer to make daylight saving time permanent, rather than standard time.

A dilemma for policymakers

Since 2018, 19 states — including much of the South and a block of states in the northwestern U.S. — have adopted laws calling for a move to permanent daylight saving time.

There’s a catch: Congress would need to pass a law to allow states to go to full-time daylight saving time, something that was in place nationwide during World War II and for an unpopular, brief stint in 1974.

The U.S. Senate passed a bill in 2022 to move to permanent daylight saving time. A similar House bill hasn't been brought to a vote.

U.S. Rep. Mike Rogers, a Republican from Alabama who introduces such a bill every term, said the airline industry, which doesn't want the scheduling complexity a change would bring, has been a factor in persuading lawmakers not to take it up.

U.S. Rep. Greg Steube, a Florida Republican, is proposing another approach.

“Why not just split the baby?” he asked. “Move it 30 minutes so it would be halfway between the two.”

Steube thinks his bill could get bipartisan support. The change would make the U.S. out of sync with most of the world — though India has taken a similar approach and in Nepal, the time is 15 minutes ahead of India.

Sleep experts prefer more daylight in the morning

Karin Johnson, the vice president of the advocacy group Save Standard Time and a professor of neurology at the University of Massachusetts Chan Medical School, said permanent standard time — with the sun straight overhead close to noon — would help students, drivers and practically everyone else function better year-round.

“Morning light is what’s really critical for setting our circadian rhythms each day,” she said.

Kenneth Wright, a professor and director of the Sleep and Chronobiology Laboratory at the University of Colorado, said the risk of fatal vehicle crashes, heart attacks and strokes increases in the days that follow turning the clock forward.

“Based on the evidence for our health and well-being and safety, the best option for us as a country now is to choose to go to permanent standard time,” he said.

Obstacles block change

Of all U.S. states, only Arizona — except the Navajo Nation — and Hawaii currently opt out of daylight saving time.

In the last two years, half a dozen states have adopted bills to switch to permanent standard time in one legislative chamber, including Virginia in February. A Virginia House committee this week recommended dropping the issue until 2027.

Most of those measures included caveats that the change would only take effect if neighboring states also made the move. For instance, Virginia would go to standard time only if Maryland and Washington, D.C., do, too. That could partially answer some of the concerns from groups including broadcasters who warn of schedule confusion. It wouldn't solve the concerns of the golf industry, which opposes full-time standard time because that would make it harder for people to get in a round in the evening.

Many full-time daylight time bills have similar provisions.

A call to make states decide

Scott Yates, a Colorado man who runs the website Lock the Clock, wants the federal government to pass a law to end the twice-a-year clock change in two years.

Under his plan, states would have to commit to either daylight saving or standard time.

As long as the clock changes persist, Yates has some advice.

“If you’re the boss, tell all your employees on Monday that they can come in an hour later,” he said. “And if you aren’t the boss, tell your boss that you think you should come in an hour later on Monday. Sleep in for safety.”