People who are “night owls” have a slightly higher risk of dying at an earlier age than people who are “morning larks,” according to a study published recently in the journal Chronobiology International.
Those earlier deaths are not more likely to be the result of cardiovascular disease, however.
Although the study’s findings are interesting, they don’t mean that being a night owl — having an internal biological clock that makes you barely intelligible at breakfast but wide-eyed at midnight — causes early death. It’s more likely that factors associated with being a night owl impacts people’s health.
“Night owls trying to live in a morning lark world may have health consequences for their bodies,” said Kristen Knutson, one of the study’s two authors and a neurologist at Northwestern University, in a released statement.
Fortunately, some of the factors that lead to those consequences for night owls can be modified, although the modifications will require greater societal understanding of the innate — and essentially fixed — nature of people’s sleep/wake cycle, or chronotype.
“This is a public health issue that can no longer be ignored,” said Malcolm von Schantz, the study’s co-author and a chronobiologist at the University of Surrey. “We should discuss allowing evening types to start and finish work later, where practical. And we need more research about how we can help evening types cope with the higher effort of keeping their body clock in synchrony with sun time.”
For the study, Knutson and von Schantz analyzed data from more than 400,000 participants in UK Biobank, a large database set up in the United Kingdom to help that country’s health officials collect information about preventing, diagnosing and treating a wide range of diseases. When first enrolled in the study, the participants ranged in age from 38 to 73, and for this particular study, they were followed for an average of 6.5 years.
The UK Biobank questionnaire asked participants about their chronotype: 27 percent said they were “definitely a morning person,” 35 percent said they were “more a morning than an evening person,” 9 percent said they were “definitely an evening person,” and 28 percent said they were “more a morning than an evening person.” The others responded with “don’t know.”
During the period of the current study, 2.4 percent of the participants — a total of 10,534 individuals — died. Knutson and von Schantz looked to see if the participants’ reported chronotype was linked to their chances of dying from any cause and, more specifically, of dying from cardiovascular disease. They also looked for links between chronotype and a variety of other health conditions.
The researchers found that the people who reported being “definitely a night person” had a 10 percent higher risk of dying during the period of the study than those who reported being “definitely a morning person.” These findings held even after adjusting for such factors as age, gender, body mass index, socioeconomic status, existing health conditions, whether they smoked and even how long they slept each night. (People who are night owls tend to get less sleep than those who are morning larks.)
The researchers did not find, however, that people in any of the chronotype categories had an increased risk of dying from cardiovascular disease.
Knutson and von Schantz did discover that night owls were at increased risk of having various medical conditions. For example, people who reported being “definitely an evening person” were almost twice as likely as their “definitely a morning person” cohorts to have a psychological condition, 30 percent more likely to have diabetes, 25 percent more likely to have a neurological disorder and 23 percent more likely to have a digestive condition.
The study wasn’t designed, however, to address why night owls may be at increased risk of having those conditions or of dying sooner than their morning lark counterparts.
“It could be that people who are up late have an internal biological clock that doesn’t match their external environment,” says Knutson. “It could be psychological stress, eating at the wrong time for their body, not exercising enough, not sleeping enough, being awake at night by yourself, maybe drug or alcohol use. There are a whole variety of unhealthy behaviors related to being up late in the dark by yourself.”
Limitations and implications
Night owls shouldn’t panic, however. The 10 percent increased chance of dying earlier is a relative risk. The absolute risk of earlier death for any particular individual night owl is quite small, as the experts who reviewed the study for the “Behind the Headlines” website of the U.K.’s National Health Service explain:
A 10% increased chance of death might sound like a lot. But if you think about the absolute risk, it’s less worrying. In this study, overall 2.4 people in every 100 died. A 10% increased chance of death would mean an increase of 0.24 in 100 if using average data for all participants. This would mean the overall risk of death for night owls would rise from 2.4 in 100 to 2.64 in 100 — about one quarter of an additional death per 100 people. We don’t have the figures to calculate the exact proportion, but it would be around this level.
The study comes with other important caveats. Most notably, it was an observational study — specifically, a prospective cohort study. Such studies can show trends and patterns within a large group of people, but they can’t prove a causal link between a specific factor and a specific outcome. Factors not identified and adjusted for in the current study might explain its results.
Another limitation is the fact that the participants were asked a single question about their chronotype — and they were asked it only once. Those responses may not accurately reflect each person’s true chronotype.
Still, as Knutson and von Schantz point out in their paper, their findings “both agree with and crucially add to previously reported associations between evening types and increased morbidity and associated risk factors.”
Fortunately, as the researchers have reported in their own earlier research, both genetics and environment play a role in whether we are night owls or morning larks (or something in between).
“You’re not doomed,” said Knutson. “Part of it you don’t have any control over and part of it you might.”
She and von Schantz note that the evening chronotype can be modified, at least a bit, by taking actions that help to advance the daily sleep/wake cycle — by using light therapy in the morning, for example, or by taking melatonin supplements in the evening.
But society needs to take action as well.
“If we can recognize these chronotypes are in part, genetically determined and not just a character flaw, jobs and work hours could have more flexibility for owls,” said Knutson. “They shouldn’t be forced to get up for an 8 a.m. shift. Make work shifts match people’s chronotypes. Some people may be better suited to night shifts.”
FMI:The study can be read in full on Chronobiology International’s website.