Their sleep behaviors were assessed in relation to the group as a whole. The earliest 25% were considered early sleepers, the latest 25% were considered late sleepers, and the middle 50% were considered medium sleepers. Categorizing sleep behaviors this way, rather than specific bedtimes, is more meaningful because different populations may have different sleep norms, Zeitzer said. “If we were doing this study with college students, 1 a.m. would obviously not be that late.”
Timing is everything
When the researchers analyzed the data, they were surprised to find that aligning with your chronotype may not be the best mental health choice for everyone — in fact, night owls may be better off living a misaligned lifestyle.
“I thought, 'This doesn't make any sense, so let me disprove it,'” Zeitzer recalled. “I spent six months trying to disprove it, and I couldn't.”
The results were clear: both morning types and evening types who went to bed late were associated with higher rates of mental disorders such as depression and anxiety.
“The worst-case scenario is that night owls stay up late,” says Zeitzer. Night owls who stay true to their chronotype are 20 to 40 percent more likely to be diagnosed with a mental illness than early risers or mid-sleepers.
Evening types who followed an earlier schedule performed better. Morning types who followed a later schedule performed worse, but not by much.
Early risers tend to be in better mental health than most, but this shouldn't come as a surprise to anyone.
The researchers found that sleep length or consistency alone could not explain these differences in mental health.
The researchers also tested the possibility that poor mental health was the cause of staying up late, rather than the other way around. They followed a subset of participants who had never been diagnosed with a mental illness for eight years. During that time, people who stayed up late and slept later were most likely to develop a mental illness.
Or is it a matter of choice?
There are many possible explanations for the link between sleep duration and mental health, but Zeitzer thinks it probably comes down to poor decisions people make in the early hours of the morning.
Many harmful behaviors, including suicidal thoughts, violent crime, alcohol and drug use, and overeating, are more prevalent at night.
One theory, known as the “midnight mind” hypothesis, suggests that neurological and physiological changes late at night may contribute to impulsivity, negative mood, poor judgment, and a tendency to take risks.
Night owls think, “I feel great. This decision I made at 3 a.m. is amazing.”
This may be why morning people seem to have an advantage even when it's late at night: They're stepping out of their comfort zone. “If I had to guess, maybe morning people who stay up late are well aware that their brains aren't functioning as well as they could, so they put off making bad decisions,” Zeitzer says.
“Whereas, night owls think, 'I feel great. That was a great decision I made at 3 a.m.'”
Another explanation could be social incongruence with mainstream chronotypes.
“There may be fewer social constraints later in the night, because fewer people are awake,” Zeitzer says. This is especially true in places like the US and UK, where people tend to be more isolated at night. In Mediterranean cultures, where people are more sociable at night, staying up late may also be better for your mental health.
Zeitzer advises night owls to get to bed before 1 a.m., but knows it's easier said than done. Getting some morning sunlight and sticking to an earlier daily routine might change your sleep patterns, but it won't change your chronotype. “Biologically speaking, it's like a rubber band; if you take a day off, your body goes back to where it wants to be,” Zeitzer says.
His team plans to explore whether specific late-night behaviors, rather than the time of day itself, are associated with poor mental health.
“If you like staying up late and you're doing things at 2 or 3 in the morning that most people would do at 10 p.m., then it might not be a problem,” he says.
But what's the fun in that?
The research was funded by the Mental Illness Research, Education and Clinical Center, the U.S. Department of Veterans Affairs and the Stanford University School of Medicine Department of Psychiatry and Behavioral Sciences 2022 Trainee Innovator Award Program.
