Every second Sunday in March marks the start of daylight saving time (DST), the annual period of the year the clocks are shifted one hour ahead. In 2021, DST officially starts at 2 a.m. on Sunday, March 14.
Jumping the clock forward and back to standard time every year was designed as a way to optimize daylight hours, which supposedly nets energy savings, prevents traffic accidents, and reduces crime, according to the U.S. Department of Transportation. But for those who live in states that practice DST (Arizona and Hawaii are the only U.S. states that don’t), research is increasingly showing that the annual time change can actually have unintended detrimental consequences to health.
In fact, the American Academy of Sleep Medicine (AASM) cites short- and long-term health risks as the basis of their argument for doing away with DST altogether, according to a position statement published October 2020 in the Journal of Clinical Sleep Medicine. And at least 29 U.S. states have introduced legislation to eliminate DST since 2015.
Cutting sleep short one hour one night might not sound that detrimental to health on first glance, says Michael Awad, MD, chief of sleep surgery at Northwestern Medicine in Chicago. But, the lost hour can have significant effects, especially among the many of us sleeping less than the recommended seven to nine hours that is recommended to begin with, Dr. Awad explains.
Research published February 2020 in Current Biology reveals that the onset of DST in the spring is associated with a 6 percent surge in fatal car crashes during the first week. “That’s a really significant number,” Awad says.
Similarly, a study published October 2018 in the Journal of Biological Rhythms found a significant uptick in general accidents and emergency room visits after the start of DST in the spring.
“The body doesn’t do very well when it’s asked to live in a different time zone,” says Elizabeth B. Klerman, MD, PhD, professor of neurology at Harvard Medical School and sleep research investigator at Massachusetts General Hospital in Boston. Changing the clocks for DST has similar effects to jet lag, which we know can be damaging to health over the long run.
Many body systems and processes (like sleep, digestion, and heart function) follow circadian rhythms, or patterns that stay consistent from day to day (roughly every 24 hours). These circadian rhythms trigger physical, mental, and behavioral changes in the body that keep us healthy — hormones get released in the morning to boost energy and rev up digestion, for example, according to the National Institute of General Medical Sciences (NIGMS).
Cues from the sun generally keep these circadian rhythms on track (via a network of cells in the brain referred to as the “body clock”), Awad says. But our behaviors — sleeping in much later than usual on a Saturday, spending a lot of time in the evening in front of bright screens (which the body registers as stimulating sunlight), or eating a big meal in the middle of the night — can send mixed messages to the body and misalign the body’s various circadian rhythms, too.
Traveling across time zones and switching the clocks for DST has a similar effect of misaligning your body’s clock to the one on the wall and the rotation of the sun, Awad explains. DST results in more hours of darkness in the morning, and more hours of daylight in the evening.
“Nighttime light and morning darkness shift your body to a later time, but the social clock has moved to an earlier time, so it’s harder to fall asleep and people get less sleep,” Dr. Klerman says. “And we know that many bad things happen from not getting enough sleep,” she adds.
Our bodies will of course adjust to the new schedule after a few days or a week, but there’s evidence the change may still affect our health, and more specifically heart health.
For example, researchers found a 24 percent increase in heart attack risk the first Monday of DST in the spring. That risk tapered off over the course of the week. Conversely, the Tuesday following “fall back” was associated with a 21 percent risk reduction. The findings were published in the journal Open Heart.
The mechanisms behind this phenomenon are still up for debate. However, it may be that DST disrupts the regular release of the stress hormone cortisol, which may increase the risk of heart attack in older adults and those with existing heart problems, according to Jamie M. Zeitzer, PhD, an associate research professor at the Stanford Center for Sleep Sciences and Medicine in Palo Alto, California.
Normally, your cortisol levels rise around the same time every morning to give you the energy you need to ease out of sleep and into a wakeful state. “If you’re getting up too early, that cortisol spike hasn’t happened yet,” Dr. Zeitzer says. Without cortisol to help, your heart has to work a lot harder to get you moving again, increasing your risk of heart problems.
While DST isn’t going away (for now, at least), there are ways to lessen its negative effects.
The more consistent your sleep schedule is before the switch, to the less of a change your body will have to make when the time change happens, Awad says. Also be sure you’re regularly getting enough sleep. If you’re sleeping eight hours per night, one night of one hour less of sleep is going to be a lot less problematic than if you’re regularly sleeping six hours of sleep and miss an hour.
If you’re not on the healthiest sleep schedule currently, use the time change as a reminder to reevaluate how much sleep you’re getting and work on solidifying good sleep habits. “Treat sleep with the same dedication as other habits, like brushing your teeth or going to the gym,” Awad says. “It’s important.”
To establish a healthy sleep routine, try to go to bed and get up at the same time every day, use your bed only for sleep and sex, limit caffeine starting in the late afternoon, and avoid bright light exposure in the evening (switch off electronic devices at least 30 minutes before bed), per recommendations from the AASM.
As DST approaches, start rolling your sleep back by about 15 minutes and moving your wakeup time 15 minutes earlier each morning. “That can help your body gradually adjust, instead of being hit with that one hour time change,” Awad says.
So, if your usual bedtime is 11 p.m., get to bed at 10:45 the Monday before DST begins. The following night, try to call it quits around 10:30, and keep going until you’ve made it to the one-hour mark.
“Another major driver of our circadian rhythm is food,” Awad says. Eating too close to bedtime can make it tough to fall asleep, because your body is too focused on digestion to think about winding down for the night.
In general, it’s a good idea to stop eating three to four hours before bedtime, Awad says. To prevent any disruption in that schedule, begin shifting your final meal (usually dinner) to an earlier time about one week before DST starts. Awad suggests shifting in 15-minute increments until you’ve hit one hour.
Before going to bed the night before DST, be sure to move all your clocks ahead. Doing so may make the time change feel less confusing, says Whitney Hardy, MD, family medicine physician at Ochsner Health Center in Lapalco, Louisiana. Then, you’ll be ready to live according to the new time as soon as you wake up the next day.
While some delay in your circadian rhythm after DST is inevitable, you can use natural sunlight to get your body clock as closely in tune with the sun clock as possible. “Getting light early in the morning is key,” Awad says.
Try to get 15 minutes of sunlight first thing in the morning. If you live in a warmer climate, you can get your sunlight outside. But even sitting next to the window while you drink your morning coffee will do the trick, Awad says. Later, avoid wake-promoting blue light from cell phones, laptops, and other electronic devices too close to bed.