Early bird gets the worm. Night owls get health problems.
People who stay up late — or all night — are more likely to develop Type 2 diabetes and have unhealthy lifestyle behaviors than morning people, according to a new study published Monday in the Annals of Internal Medicine.
And, scientists say, you can’t necessarily change these habits to improve your health — sleep patterns are actually defined by a person’s circadian preference, or chronotype. Having an internal body clock that is, in part genetically, set for staying up late makes it hard for a night owl to become an early bird, who naturally wakes up at dawn and goes to bed early.
Researchers from Brigham and Women’s Hospital in Boston had previously discovered that people with irregular sleep patterns are at a higher risk of diabetes and cardiovascular disease, and that those with an evening chronotype tend to have irregular sleep schedules — which led to studying the correlation between chronotype and diabetes risk, while accounting for lifestyle factors.
The researchers looked at 63,676 nurses participating in the Nurses’ Health Study II, all between the ages of 45 and 62 and with no history of cancer, cardiovascular disease or diabetes from 2009 to 2017.
Data included self-reported chronotype — whether participants perceived themselves as either a morning or night person — quality of diet, weight and body mass index, sleep timing, smoking behaviors, alcohol use, physical activity and family history of diabetes. Diabetes status was also determined from medical records.
“Chronotype, or circadian preference, refers to a person’s preferred timing of sleep and waking and is partly genetically determined so it may be difficult to change,” said corresponding author Tianyi Huang, an associate epidemiologist in Brigham’s Channing Division of Network Medicine, said in a media release.
About 11% of participants self-reported having a “definite evening” chronotype, while 35% reported a “definite morning” chronotype. Everyone else was categorized as “intermediate” — meaning either they didn’t identify with either chronotype, or identified with one just slightly more than the other.
“People who think they are ‘night owls’ may need to pay more attention to their lifestyle because their evening chronotype may add increased risk for Type 2 diabetes,” Huang added
Before accounting for the destructive lifestyle of night owls, the evening chronotype had a 72% increased risk for diabetes.
Even after the researchers took into account the impact of a night owl’s unhealthy lifestyle, those who stayed up late still were about 19% more likely to develop diabetes.
“When we controlled for unhealthy lifestyle behaviors, the strong association between chronotype and diabetes risk was reduced but still remained, which means that lifestyle factors explain a notable proportion of this association,” said first author Sina Kianersi, a postdoctoral research fellow in the Brigham’s CDNM.
The analysis found that those with later sleep and wake times were likelier to eat unhealthily, exercise and sleep less, smoke cigarettes and have a higher BMI.
Only 6% of the participants with the healthiest lifestyles had evening chronotypes, while 25% of those with the unhealthiest lifestyles were night birds.
The link between chronotype and diabetes risk was only found in nurses who worked day shifts, not those who worked the overnight shift.
“When chronotype was not matched with work hours we saw an increase in Type 2 diabetes risk,” said Huang. “That was another very interesting finding suggesting that more personalized work scheduling could be beneficial.”
Researchers noted that since the Nurses’ Health Study mainly consists of white female nurses, further research is needed to determine if the patterns hold across all populations.
It’s also possible that other outlying factors could contribute to setting chronotype, establishing unhealthy habits and incurring the risk of diabetes, so correlation cannot necessarily be equated with causation yet.
“If we are able to determine a causal link between chronotype and diabetes or other diseases, physicians could better tailor prevention strategies for their patients,” Kianersi said.
Researchers plan to expand their investigation to larger and more diverse populations, looking at the genetic determinants of chronotype and its association with cardiovascular disease and diabetes.
