Most of the U.S. will “spring forward” Sunday for daylight saving time, setting clocks ahead by one hour at 2 a.m. in most states. For many people, that calendar adjustment means losing an hour of sleep right as the week begins, which can affect more than how rested someone feels the next day.
Health reporting around the seasonal change describes a body clock that responds to light exposure, particularly sunlight in the morning and darkness at night. The circadian rhythm — often described as a roughly 24-hour cycle — helps determine when people become sleepy and when they feel more alert, and the shift to lighter evenings can interfere with that timing.
The article said that darker mornings and more evening light can knock the body clock out of sync, and that daylight saving time can usher in sleep trouble for weeks or longer. It also pointed to evidence that the March time change is followed by a short-term uptick in heart attacks and strokes.
The mechanism described is tied to melatonin, a hormone that typically begins to surge in the evening to trigger drowsiness. With daylight saving time, the extra hour of light in the evening delays that surge, and the cycle can get out of alignment.
Researchers cited in the coverage also linked the time change to transportation and cardiovascular risks. The reporting said fatal car crashes temporarily jump in the first few days after the spring time change, with the risk highest in the morning, and researchers attributed that pattern to sleep deprivation.
For heart and brain events, the American Heart Association said studies suggest an uptick in heart attacks on the Monday after daylight saving time begins, and strokes for two days afterward. Doctors already know that heart attacks are more common on Mondays and that they can be more frequent in the morning, when blood is more clot-prone, according to the reporting, while researchers said they do not know why the time change would intensify the Monday connection.
The guidance included in the coverage focuses on making the transition easier for the circadian system. It recommended going outside for early morning sunshine during the first week of daylight saving time to help reset the internal clock, and it also advised shifting routine timing — such as dinner and exercise — to help cue the body to adapt.
The reporting also cautioned that afternoon naps and caffeine, and exposure to evening light from phones and other electronics, can make it harder to move up to an earlier bedtime. It described the challenge as especially relevant for people who already do not get the recommended amount of nightly shuteye.
The seasonal time shift has also fueled periodic debate about whether the U.S. should eliminate the change altogether. The reporting said President Donald Trump previously promised to eliminate daylight saving time before starting his second term, and it described the bipartisan Sunshine Protection Act that would make daylight saving time permanent as having repeatedly stalled in Congress.
But health organizations cited in the coverage said ending the time switches would still require choosing a consistent time year-round. The American Medical Association and American Academy of Sleep Medicine said they support doing away with the time changes and agreed that sticking with standard time year-round would align better with the sun and human biology for more consistent sleep.
In addition to the national “spring forward” shift, the coverage said Hawaii and most of Arizona do not make the spring switch and remain on standard time year-round, along with Puerto Rico, American Samoa, Guam and the U.S. Virgin Islands. It also noted that worldwide, dozens of countries observe daylight saving time on different start and end dates.