Before Clocks Fall Back Nov. 1, Here’s How Morning Light Shapes Your Sleep

Most Americans say they’re tired of changing their clocks twice a year. A Gallup poll found that 54% want to end the time change, but people disagree about whether the country should stay on daylight saving time or standard time permanently. Congress is divided too. The House passed a bill in July that would make daylight saving time permanent, while another proposal would keep standard time all year.

For sleep experts, the choice comes down to biology. Feby Puravath Manikat, M.D., a spokesperson for the American Academy of Sleep Medicine (AASM), explained why morning light matters and what’s at stake in the debate.

Morning light sets the body’s clock

The body runs on an internal clock, known as the circadian rhythm, which helps decide when people feel alert, when they feel sleepy and when other biological functions happen.

“Sunlight is the most powerful external cue for synchronizing the body’s internal clock with the natural day-night cycle,” Manikat said.

Daylight saving time moves daylight later in the day, giving more light in the evening and less in the morning. Manikat explained that this “can delay the body’s internal clock, making it harder to wake up and feel alert in the morning because the body lacks the light cues that signal it’s time to be awake.”

Standard time, by contrast, “aligns more closely with the sun and human circadian biology,” she said.

That mismatch can affect more than sleep. Manikat noted that when circadian rhythms fall out of sync, the misalignment “has been associated with increased risks to cardiovascular health, metabolic health and mood.” The AASM has also linked the spring switch to daylight saving time with higher rates of heart problems, mood disorders and car crashes.

What the 1970s taught the country

The U.S. has already tried year-round daylight saving time. In January 1974, the country made the switch to save energy, but it quickly became unpopular as many Americans, including children heading to school, faced dark mornings.

According to a 1974 Department of Transportation report, public support for the change dropped from 79% in December 1973 to 42% by February 1974. Congress ended the experiment that fall.

“Sleep experts believe this history remains relevant because the underlying biology has not changed,” Manikat said.

Teens may feel the effects most

Teenagers are especially sensitive to the loss of morning light. During puberty, the body’s clock naturally shifts later, so teens feel sleepy later at night and want to sleep later in the morning.

“This means that when school schedules require them to get up early, they may be trying to wake up when their bodies are still biologically programmed to sleep,” Manikat said.

Under permanent daylight saving time, teens could be getting ready for school or commuting in the dark, while extra evening light could push their bedtimes even later. Teens should get eight to 10 hours of sleep a night, but most get fewer than eight on school nights. That shortfall can lead to daytime sleepiness, trouble learning, mood problems and higher risks for new drivers.

“This is a question that largely impacts adolescent health and safety,” she said.

The winter morning trade-off

Supporters of permanent daylight saving time point to the appeal of longer evenings. Manikat said that’s understandable, but the winter trade-off is significant. In some parts of the country, the sun wouldn’t rise until after 9 a.m., and dark mornings can also create hazards for children waiting for the bus and people commuting to work.

“Although people may understandably value longer summer evenings, the effects of a time policy need to be considered across all seasons, not just the months when daylight lasts longer,” she said.

For that reason, the AASM supports ending seasonal clock changes and adopting permanent standard time.

Getting through the Nov. 1 time change

Unless Congress acts first, clocks will fall back one hour on Sunday, Nov. 1. Manikat’s top advice is to prioritize sleep, keep a consistent schedule and get outside for morning sunlight that week.

“Even though we gain an hour when we ‘fall back,’ it’s important not to treat that extra hour as a reason to stay up later,” she said. “Instead, use it as an opportunity to get the sleep your body needs.”

She suggests going to bed at your usual time and setting your clocks back just before getting into bed. Adults should aim for at least seven hours of sleep a night before and after the change. If you feel drowsy that week, take extra care behind the wheel.