A person’s chronotype is their inclination to sleep at certain times, and it often doesn’t match the actual time they go to bed because this is influenced by the need to conform to social and work norms. This mismatch can have an impact on their mental health. That’s according to a new study by researchers at Stanford University, which has found that night owls who follow their natural inclination to stay up late are at higher risk of mental disorders.
Researchers surveyed 73,888 adults to compare participants’ preferred sleep chronotype—that is, their ideal sleep schedule—with their actual sleep behavior and found that regardless of what time they prefer to go to bed, everyone benefits from getting to sleep early, with both early birds and night owls reporting higher rates of mental and behavioral disorders if they stayed up late.
“We found that aligning with your chronotype isn’t crucial here; what’s really important is that staying up late isn’t good for your mental health,” said Jamie Zeitzer, a professor of psychiatry and behavioral sciences and senior author of the study. “What we don’t know is why.” In any case, their findings, which have been published in Psychiatry Research, recommend turning off the lights before 1 a.m.
More depression and anxiety in people who go to bed late
The results weren’t exactly what the researchers had expected. An earlier study by Zeitzer’s team had suggested that women with cancer who slept against their chronotype had shorter lives. “There’s a lot of data that indicates that living aligned with your chronotype is very important,” Zeitzer said. “That was our expectation.”
The researchers decided to study chronotype alignment in a broader population. They examined middle-aged and older adults in the United Kingdom, who were asked about their sleep habits, including their morning or evening preference. They were sent a wearable accelerometer to track their sleep for seven days.
Participants’ mental health was determined through their medical records. The researchers included any mental or behavioral disorders listed in the International Classification of Diseases. Among the 73,880 participants, 19,065 identified themselves as morning types, 6,844 as evening types, and 47,979 somewhere in between.
Their sleep behavior was assessed relative to the entire group. The earliest 25% were considered early risers, the latest 25% were considered night owls, and the middle 50%. Categorizing sleep behavior this way, rather than by specific hours, is more meaningful because different populations may have different sleep norms, Zeitzer explained. “If we were doing this study on college students, 1 a.m. obviously wouldn’t be that late.”
Night owls who were true to their chronotype were 20% to 40% more likely to be diagnosed with a mental health disorder, compared to night owls who followed an early or mid-day sleep schedule.
When researchers analyzed the data, they were surprised to find that aligning with the chronotype wasn’t best for everyone’s mental health. In fact, it was better for night owls to lead a misaligned life. “I thought, let’s try to disprove this, because this doesn’t make sense,” Zeitzer recalled. “We spent six months trying to disprove it and we couldn’t.”
The results were clear: Both morning types and evening types who went to bed late had higher rates of mental health disorders, including depression and anxiety. “The worst case scenario is definitely the people who go to bed late,” Zeitzer said. Night owls who stuck to their chronotype were 20% to 40% more likely to be diagnosed with a mental health disorder, compared with night owls who followed an early or mid-morning sleep schedule.
Evening types who followed an earlier schedule fared better. Morning types who followed a later schedule also suffered, but not as much. Early risers who rose with the sun tended to have the best mental health of all, which surprised no one.
The researchers found that sleep duration and sleep schedule consistency could not explain these differences in mental health. They also tested the possibility that it was poor mental health that was causing people to stay up late, rather than the other way around. They tracked a subset of participants who had no previous diagnosis of a mental disorder over the next eight years. During that time, night owls who slept late were the most likely to develop a mental health disorder.
The “mind after midnight” hypothesis
There may be many explanations for the link between sleep timing and mental well-being, but Zeitzer believes it likely stems from the poor decisions people make in the early hours of the morning. Many harmful behaviors are more common at night, including suicidal thoughts, violent crime, alcohol and drug use, and overeating. One theory, known as the “mind after midnight” hypothesis, suggests that neurological and physiological changes at night may foster impulsivity, negative mood, impaired judgment, and increased risk-taking.
That might explain why even late at night, morning types seem to have an advantage: They’re aware of being outside their comfort zone. “If I had to hazard a guess, morning people who are up late are very aware that their brain isn’t working quite right, so they can avoid making bad decisions,” Zeitzer said. “Meanwhile, the evening person who is up late is thinking, ‘I feel great. This is a great decision I’m making at 3 in the morning.’”
Another explanation could be a social mismatch with the predominant chronotype. “Maybe there are fewer social restrictions late at night because fewer people are awake,” Zeitzer said. That’s especially true in places like the United States and the United Kingdom, where people tend to be more isolated in the evenings. In a Mediterranean culture, where nights are more sociable, staying up might even be beneficial for mental health.
While Zeitzer advises night owls to go to sleep before 1 a.m., she knows that’s easier said than done. Getting sunlight in the morning and maintaining an earlier routine every weekday might change your sleep patterns, but it doesn’t change your chronotype. “Biologically speaking, it’s a lot like a rubber band: You take a day off and you’re back to where your body wants to be,” she said.
Her team plans to examine whether certain nighttime behaviors, rather than the schedule itself, are linked to poor mental health. “If you like staying up late and you just do what people normally do at 10 p.m., but you do it at 2 or 3 a.m., maybe that’s not a problem,” she concludes.
