Night owls have 10% higher mortality risk, study says
If the early bird catches the worm, what is the night owl more likely to catch? According to a new study, it’s diabetes, psychological problems and an increased risk of dying.
The study, published Thursday in the journal Chronobiology International, tracked almost half a million adults in the United Kingdom over an average of 6½ years. The researchers found that those people who identified as “definite evening types” at the beginning of the study had a 10% increased risk of all-cause mortality compared with “definite morning types.”
Night owls were also more likely to have diabetes, neurological disorders, psychological disorders, gastrointestinal disorders and respiratory disorders, according to Kristen Knutson, associate professor of neurology at Northwestern’s Feinberg School of Medicine and a leading author of the study.
“What we think might be happening is, there’s a problem for the night owl who’s trying to live in the morning lark world,” Knutson said. “This mismatch between their internal clock and their external world could lead to problems for their health over the long run, especially if their schedule is irregular.
“Previous work has shown that people who are evening types — are night owls — tend to have worse health profiles, including things like diabetes and heart disease,” Knutson added. “But this is really the first study to look at mortality.”
The researchers relied on data from the UK Biobank — a large prospective cohort study conducted between 2006 and 2010 that investigated risk factors for major diseases in men and women 37 to 73 years of age. In order to evaluate natural circadian rhythm, otherwise known as their chronotype, participants were asked to identify as “definitely a morning person,” “more a morning person than evening person,” “more an evening than a morning person” or “definitely an evening person.”
Of the 433,268 participants, approximately 10,000 died during the study’s 6½-year followup period. After controlling for factors such as age, sex, ethnicity, body mass index, smoking status and sleep duration, the researchers found that those who identified as “definite evening types” had a 10% increased risk of dying during the followup period compared with those who identified as “definite morning types.”
The risk of death was not increased for those who identified as “more a morning person” or “more an evening person” compared with the morning larks, according to the report.
“This is just one piece of the puzzle,” said Jamie Zeitzer, associate professor of psychiatry and behavioral sciences (sleep medicine) at the Stanford School of Medicine, who was not involved in the research.
“The findings for the mortality actually weren’t as robust as I would have hoped. … I think they would have had stronger results if, instead of just looking at chronotype, they had looked at chronotype alignment: So, are people going to bed at their correct time?” Zeitzer added.
In addition to overall mortality, being a night owl was associated with a number of health problems such as psychological, neurological, gastrointestinal and respiratory disorders.
The association was strongest for psychological disorders: Those who identified as “definite evening types” were nearly twice as likely to report having a psychological illness than those who were “definite morning types,” the study found.
“It’s interesting,” Zeitzer said. “And it would definitely take some follow-up to see what that means. Is that depression? Is that anxiety? Are there specific psychological phenomena that are more or less related to chronotype, especially the disparity between your chronotype preferred timing and the actual timing of sleep?”
Although the study did not look at the specific causes of death, research has suggested that night owls are more likely to develop cardiovascular disease and certain types of cancer such as prostate and breast cancer.
A 2014 study also showed that those who stay up late had less white matter in certain areas of the brain associated with depression. White matter consists of nerve projections that relay and coordinate communication between different areas of the nervous system.
According to Knutson, a person’s chronotype is probably a mixture of inherited and environmental factors.
“Whether or not you’re a night owl is partly determined by your genes, which obviously you can’t change, but it’s not entirely a given,” Knutson said.
Some strategies known to help people trying to switch to an earlier schedule include gradually advancing your bedtime and avoiding the use of technology at night, according to Knutson.
“I want to emphasize the gradual aspect. You can’t suddenly tonight just go to bed three hours earlier. It’s not going to work,” Knutson said.
“You also need to really avoid light at night, including your smartphone and your tablets,” she added. “That not only makes it hard to fall asleep; it’s also a signal to your clock to start being later again.”
For those who still struggle with mornings, finding a job that has flexible hours or hours more consistent with your biological clock could be a solution.
“You can find a job that starts later, but that’s not a particularly useful piece of advice for a lot of people,” Zeitzer said.
Knutson added, “employers should recognize that some of their employees are going to be morning types and some are going to be evening types.
“And if their work hours were flexible to reflect their biological clock preference and allow the night owls to have a later work schedule, that would be preferable for them and potentially better for their health and their productivity if they’re working at the time that’s best for them.”
Although the researchers controlled for ethnicity, nearly 94% of the participants identified as Caucasian, meaning the results may not be generalizable to other demographics, according to Zeitzer.
“It’s limited because of that,” he said. “It’s strong in that it’s a big sample of nearly half a million people, but it is mainly Caucasians of Irish or English descent.”
“It’s not intrinsically chronotype that’s bad; it’s chronotype plus our society … and not all societies are the same,” Zeitzer added. “If you looked in Spain, where people are much later in terms of when they go to work, my guess is that the health consequences are probably less than in the UK.”
Chronotype was also measured based on self-reports rather than objective measures, one of the study’s main limitations, according to Knutson.
But the study should still be a wake-up call for night owls, who may want to take extra efforts to maintain a healthy lifestyle, she said.
“An important message here is for night owls to realize that they have these potential health problems and therefore need to be more vigilant about maintaining a healthy lifestyle,” Knutson added.
“Eating right, exercising, getting enough sleep — all of these things are important, and maybe particularly so for night owls.”