Night owls—people whose natural body clock, or chronotype, skews to late sleep and wake times—are already forced to wake up too early for office jobs and to deal with derision from early birds. And now comes a new affront: research concluding that they appear to decline faster, cognitively, than morning people.
To look into this, dementia researcher Ana Wenzler at the University of Groningen in the Netherlands analyzed sleep-based questionnaires through a large national study, BIRD-NL Project. She was able to determine people’s chronotypes and found that 52% were morning people, 44% intermediate, and only about 5% night owls—different from the general global population breakdown, where typically 30% are night owls, 40% early birds, and the rest in between.
Next, Wenzler looked at the results of a cognitive function test over a 10-year period to see how the scores differed at the end of the decade.
Her conclusion was that evening people saw faster cognitive decline. But every night owl may not have the same risk.
Study looked at executive function
“We found that 25% of the effect was due to lower sleep quality and smoking,” Wenzler tells Fortune. “So, having a healthy lifestyle could lower the negative effect of having a late chronotype a bit.”
She says that, for this study, she only looked into the executive function of the brain, so more research is needed into how chronotype affects memory, language, and other cognitive aspects.
But the increased risk here, interestingly, was found mostly in highly educated people. “That probably has to do with their sleep rhythm,” Wenzler said in a news release. “They are often people who have to go back to work early in the morning and are therefore more likely to sleep too short, giving their brains too little rest.”
This tracks with a previous body of research showing that night owls, compared with early risers, face various health risks—a 30% higher risk of diabetes, nearly double the odds of depression and other psychological disorders, increased heart disease risk, and a 10% higher all-cause mortality risk.
“All of this evidence, to me at least, impresses the fact that when we do not sleep in harmony with our chronotype, the ensuing sleep disruption that unfolds has consequences,” Matt Walker, a professor of neuroscience and psychology at the University of California, Berkeley, and founder and director of the Center for Human Sleep Science, previously told Fortune.
He added, “There is vast variability in chronotype, and it’s important to sleep in harmony with yours.” (You can determine it with this free calculator.)
Can you change your chronotype?
But if work and other factors won’t allow you to stay up till 2 a.m. and sleep in until 10 a.m., could you push yourself to become an early bird?
“Some studies showed that intensive intervention could help change your chronotype… but only by a few hours,” Wenzler says. “But forcing yourself to get up early every day while you are an extreme evening person will not make you a morning person. In these cases, it might be best to adapt your life, as much as possible, to your chronotype.”
Walker also noted that only slight shifts are really possible, and that the ongoing, disciplined interventions that are required to truly change chronotypes are “just not tenable,” he said. “Let night owls sleep as they were biologically designed. At least, that’s how I feel on the basis of the science and medicine of the data.”
So, is the cognitive health of night owls just simply doomed?
“If these individuals are doomed is hard to say, as we only had a follow-up of 10 years,” says Wenzler, explaining that the true long-term effects—particularly whether or not night owls are more likely to develop dementia—need further investigation.
“Faster cognitive decline in middle age does not necessarily mean a higher risk of dementia,” she said in the news release. “With our research, we hope to find out more about this. This will ultimately help us to be able to give people informed advice on how to try to prevent dementia.”
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