Don’t lose sleep over daylight saving time

Every year, people literally lose sleep over the changing of the clock. We set our clocks ahead one hour when daylight saving time (DST) begins (which this year will be March 10 at 2 a.m.), but do we set back our health in the process?

“The immediate impact of that first day is that you’re probably going to get an hour less of sleep,” said David J. Earnest, PhD, a professor at the Texas A&M University School of Medicine who studies circadian or 24-hour rhythms controlled by our internal body clocks. “In theory, a one-hour time change shouldn’t really take more than a day or two to adapt to, but sometimes it does—for various reasons.”

These internal biological clocks regulate a number of physiological functions—from hormone release and metabolism to fatigue and alertness. During the transition on or off DST, everything feels just a little out of sync.

“The easiest and best thing to do is to make the adjustment immediately and eat and sleep that very first day according to the new time,” Earnest added. “It’s pretty much common sense, but it can be very difficult.”

The change may be especially problematic for teenagers and for those with sensitive body clocks. “There’s a lot of variation in terms of how well our bodies respond,” Earnest said. People may have noticed these differences when traveling with friends or family and some members of the group adapt more easily to the new time zone than others do.

“Shifting to an earlier time is just like flying eastward, and our bodies adapt much more easily when we fly westward, or have the time change in the fall when we get an extra hour of sleep,” Earnest said. “The time change in the spring—when we’re pulled from our beds an hour earlier—is more significant.”

A number of studies have hinted that those at risk for heart attacks or strokes may be more likely to have one shortly after the beginning of DST, but most—if not all—would have happened around that time regardless. It is also worth noting that the risk to any one individual is quite small.

Still, even if it’s not deadly, the time change can make life difficult. “Disruption of circadian rhythms and loss of sleep leads to mood changes and poor cognitive functioning,” Earnest said. Some evidence does suggest that the risk of car accidents may increase the Monday after DST begins.

With all of these downsides, why do we have DST at all?

It’s nice to leave work at 5 p.m. or 6 p.m. and still have several hours of useful daylight remaining, but by that logic, should DST be the standard all year long? “If we were staying on daylight savings time, then when you get up and go to work in the morning in the winter, it’s dark, which can have safety implications,” Earnest said. On the flip side, extra daylight in the evening may lead to less crime.

Many Americans support the idea of making daylight saving time permanent, while two states—Arizona and Hawaii—don’t observe DST, opting instead to remain on standard time year-round. As recently as 2022, the U.S. Senate passed legislation that would make DST permanent starting in 2023, but it ultimately fell through.

The idea of DST seemed to be popular during war years, from the establishment of DST in 1918 (during World War I), its repeal in 1919 after the end of the war and its re-establishment during World War II from Feb. 9, 1942 to Sept. 30, 1945. The Uniform Time Act of 1966 provided standardization for the beginning and ending dates of daylight time in the U.S. but allowed for local exemptions from its observance. These exemptions are why Hawaii and Arizona aren’t required to observe DST. Other states, including the most populous one, California, have considered doing the same.

Earnest notes that it is also important to change mealtimes to be in-line with the time change because conflicting signals might confuse your body clocks. “If your body expects food to be forthcoming and it starts cranking up metabolism, and then you don’t eat, that causes problems,” Earnest said. This means that someone who has been waking up at 7 a.m. and eating lunch at noon should continue doing so after DST begins, even though both these times have shifted forward one hour in real time. The fact that DST begins on a Sunday means that for most people, there is an extra day to adjust before returning to work or school on Monday. Earnest suggests taking advantage of that fact.

“For the springtime change, because that is a little more difficult, maybe shifting half an hour per day and doing it in two days would be good,” Earnest said. “But either way, the best philosophy—because one hour is a reasonable move—is to just make yourself get up on Sunday at the time you need to be up on Monday morning and perhaps get some early morning sunshine.”

Originally published March 9, 2018; updated March 5, 2024