Night owls may be twice as likely as early risers to underperform at work, study suggests

The traditional working day doesn't benefit night owls, a new study from Finland has suggested.

The traditional working day doesn't benefit night owls, with people who prefer to stay up late twice as likely to underperform at work as early birds, a new study from Finland has suggested.

Early risers -- people who have a morning chronotype -- tend to work better early in the morning, while evening types are the reverse. This inner clock is thought to be largely genetic, but work schedules, family life and exposure to daylight also play a role.

Chronotype is your time-of-day preference for sleep and other activities, and reflects differences in an individual's underlying circadian rhythm. This internal process plays a role in sleep patterns, metabolism and body temperature and influences hormones.

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The researchers asked 5,881 individuals born in 1966 in northern Finland about their working life and health and questioned them about their sleep patterns to determine what their natural chronotype was in 2012 when they were 46 years old. The study participants were monitored over a period of four years.

Ten percent of the men and 12% of the women were "evening types," 72% of whom worked in day jobs, the researchers found. The rest of the people largely split evenly into early risers, or what the researchers termed intermediate chronotypes.

A quarter of people classified as evening types rated their own performance at work as poor using what the researchers described as an internationally accepted scale developed to identify individuals with poor work ability and a higher risk of retiring early because of disability. This was a significantly higher proportion than among early birds or intermediate chronotypes, the research said.

The odds of underperformance were twice as high among the night owls as they were among the early birds in both sexes even after taking account of potentially influential factors, such as sleep duration and morning working hours, found the study, which published Tuesday in the journal Occupational & Environmental Medicine.

"If evening types have to work in the early morning, they won't rate their work ability as high as morning types. The reverse would be true as well. If normal business hours were 3 p.m. to 11 p.m., the early morning types would feel worse than evening types," said Kristen Knutson, an associate professor at Northwestern University, who researches the association between sleep, circadian rhythms and cardiometabolic diseases, including diabetes, obesity and cardiovascular disease.

"The underlying mechanism is our internal biological clock that dictates the time of day we perform best," said Knutson, who wasn't involved in the research.

While the population studied was from one area of Finland, Knutson said the findings "likely apply" to the United States given that biological clocks are universal. However, the researchers pointed out that office work in Finland starts early -- typically at 8 a.m., and manual work even earlier -- so their findings might not be applicable everywhere, and the topic should be studied further.

"This was the first population-level study to provide evidence that evening chronotype could be related to poor work ability," said the study authors Dr. Tapio Räihä and Leena Ala-Mursula, professor of occupational health care, from the Center for Life Course Health Research at the Univeristy of Oulu, Finland, in an email.

"We acknowledge that these observational findings are new, and need to be confirmed in other studies. Still, our results are well in line with previous evidence on eveningness being related to poorer health and functioning," they added, using their word for evening chronotypes.

Suzanne Hood, an associate professor at Bishop's University in Quebec, Canada, said that night owls shouldn't be alarmed by the findings.

Rating job performance doesn't necessarily tell you about the quality of the work in real terms, noted Hood, who studies the body's circadian rhythms. Also, the study was observational -- it doesn't mean that being a night owl makes you less able to work. Plus, employers could benefit from people with different chronotypes.

"For example, the employee who seems like a slow starter in the morning might be the person who's most able to work effectively into the evening to meet an important deadline," said Hood, who wasn't involved in the research.

"If there is some opportunity for flexibility in scheduling, allowing employees some control over what time of day they complete their work may help to optimize performance and productivity."

However, she said there was lots of evidence to show "that chronotype can affect your cognitive sharpness, which can play into performance on the job or in the classroom."

"This influence is clear when you challenge someone to pay attention and remember information at a time of day outside of their preference: for example, asking an evening person to deliver an important presentation to clients at a 7:30 a.m. breakfast meeting. Some people may have experienced this kind of mental fogginess in the throes of jet lag."

Hood said there were several mechanisms that could be at play, including sleep deprivation and how your body's daily rhythms affect how you respond to information and different environments.

"Due to differences in readiness to fall asleep, the evening person arriving at the office at 8 a.m. may have had only 6 hours of sleep, whereas the morning person arriving at the same time had 8 hours," she explained.

"I'd encourage people whose work schedule is out of sync with their chronotype to try to follow a regular sleep schedule to avoid becoming sleep deprived," Hood said. "Chronotypes are a bit malleable, so we can shift our preferred times of day around a little by keeping a daily routine of sleeping and waking times. "

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