On the eve of Daylight Saving Time, I flew home to Vermont from California. Crossing several time zones, I arrived near midnight. At 2 a.m., the clock jumped ahead an hour, leaving me discombobulated.
“How messed up am I?” I asked sleep researcher and evolutionary anthropologist David Samson days later. Jet lag can make people feel moody and hungry at weird times, but my extreme state probably masked chronic sleep dysregulation, he told me.
For most of human history, people woke with the sun and slept with the stars. Environmental cues like light and temperature synchronized the body’s clock, or circadian rhythm, to the day-night cycle. Nowadays, many of us spend more time indoors than out, where we bathe in artificial light and temperatures set for optimal comfort.
It’s a “circadian jail cell,” says Samson, of the University of Toronto. The body, he says, “is a receptacle of data. If we’re blocking the data, our physiology’s got nothing to work on.”
And a misaligned body clock could be cause for concern, as it disrupts hormone release and other bodily processes, Samson says. Circadian disruption has been linked to depression, cancers, heart disease and inflammation.
In fact, when we sleep may be a bigger problem than the amount we sleep. Samson and a colleague recently reviewed 54 sleep studies conducted between 1967 and 2022 that analyzed over 5,100 people from 21 countries. People in the industrialized world averaged 7.1 hours of sleep per night, the pair reported February 26 in Proceedings of the Royal Society B. People in the nonindustrialized world, most without electricity access and living more like humans of the past, got on average 42 minutes less sleep per night, or 6.4 hours total.
Though people in the industrialized world get enough sleep on average, they tend to sleep out of sync with their body clocks, Samson says. In studies measuring individuals’ activity levels throughout the day — a proxy for circadian rhythm — people in the nonindustrialized world lived more in tune with the sun than people in the industrialized world.
Other researchers question this line of reasoning. Neuroscientist Horacio de la Iglesia argues that the “traditional” foraging societies in Samson’s work might be outliers. His data suggest that people in traditional communities with few outside stressors, such as predators, but without electricity sleep as much as nine hours a night.
It’s hard to separate sleep deprivation from circadian disruptions, says de la Iglesia, of the University of Washington in Seattle. When communities get electricity, people start sleeping less and later than before, his research shows. A person who goes to sleep late may still have to get up early for work. “When your circadian clock is misaligned, you also sleep less,” he says.
For de la Iglesia, one path forward is for society to be more flexible with the start of the work or school day. Imagine a world in which someone with a 1 a.m. bedtime can wake up eight hours later without issue.
Samson argues that getting your body’s clock on track is still important, especially if you feel out of sorts after a full night’s sleep. Practicing good “chronohygiene,” he says, can mean making indoor spaces more like the outdoors. Set the thermostat so that your home is cooler at night and warmer during the day. Or install lights that blaze blue come morning and dim and redden alongside sundown.
Don’t fret about blue light from smartphones and other screens, says time-use expert Juana Lamote de Grignon Perez of University College London. Despite warnings about the impact on sleep, “the amount of light that these devices emit is negligible,” she says. A five-minute morning walk “has a much stronger impact on your body than checking your phone for 30 minutes.”
Of course, doomscrolling while in bed may be keeping you up for other reasons. So maybe it is best to put the phone down.