People who prefer to go to bed late and wake up late may be putting their health at risk, according to a new study.
It's no secret that the quality of someone's sleep habits impacts their wellbeing. But evidence also points to the timing of someone's nightly routine as a factor in overall health and lifestyle.
The new study, published in the Annals of Internal Medicine journal, found that night owls, or people with “evening chronotypes,” were more likely to have unhealthy lifestyle habits and to develop diabetes.
“People with 'night owl' are at a 72% increased risk of developing diabetes—and that’s a substantial increased risk when we compare them to early birds,” Sina Kianersi, DVM, PhD, first study author and postdoctoral research fellow at Brigham and Women's Hospital and Harvard Medical School, told Health.
The research team also found that night owls were more likely to smoke, exercise infrequently, and engage in other negative lifestyle behaviors.
A chronotype is a natural inclination the body has for waking and resting at certain times—generally, people can be categorized as having an "early bird" or "night owl" chronotype. Someone's chronotype can impact appetite, feelings of alertness/sleepiness, and core body temperature.
Kianersi explained that because the study was done in a large cohort of middle-aged female nurses, there may be some limitations to its applicability. However, the research builds on the general idea that a person’s sleep preferences can have major implications for their health.
"The effect of shift work [on] our metabolism and insulin resistance have been in the literature within the last decade or more," Betul Hatipoglu, MD, professor of medicine at Case Western Reserve University School of Medicine, told Health in an email. "However the article describes that the increase was observed in day shift workers. That is an interesting observation."
Here’s what experts had to say about the link between sleep preferences and overall health, why night owls might be at a higher diabetes risk, and what people can do to ensure their chronotype doesn't get in the way of their wellbeing.
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To understand the relationship between chronotype and diabetes, Kianersi and his team gave over 60,000 female nurses a survey where they could rank their sleep preferences on a spectrum—about 35% of the participants identified as definite early birds, while about 11% identified as definite night owls.
When the study started, none of the participants had a history of cancer, cardiovascular disease, or diabetes. They were asked to report any new diabetes diagnosis until the study ended in 2017.
Researchers also used a questionnaire to determine the nurses’ lifestyle in six areas: alcohol use, body mass index (BMI), physical activity levels, smoking status, sleep duration, and diet.
Overall, self-proclaimed night owls tended to also have a less healthy lifestyle based on these factors.
According to the questionnaire, night owls tended to smoke more, have an unhealthy sleep duration, and not meet exercise recommendations. There was also a significant association between being a night owl and having a poorer diet and a higher BMI.
Kianersi explained that the other major finding from the research was that night owl nurses saw a 72% increased risk of diabetes. But, once unhealthy lifestyle behaviors were accounted for, the additional diabetes risk for this chronotype dropped to 19%.
This means night owls’ lifestyle is largely to blame for making their diabetes risk worse, Kianersi said, though their risk, in general, was still elevated.
These aren’t necessarily novel findings—recently published studies have found that being a night owl could put someone at an elevated risk of diabetes and cardiovascular disease, and that night owls are more likely to use tobacco and alcohol.
But, according to Kianersi, the link between lifestyle factors and night owls’ elevated diabetes risk is what sets this study's findings apart from previous research.
Unhealthy lifestyle behaviors account for most of night owls’ elevated diabetes risk, which aligns with what scientists already know about the disease.
The Centers for Disease Control and Prevention list the following as risk factors for type 2 diabetes:
These factors were also reflected in the study.
However, even after accounting for these behaviors, night owls were still at a 19% increased risk of diabetes as compared to early birds. It’s not totally clear why this is the case, though this stat could indicate that “there might be something [beyond] lifestyle that is causing this relationship,” Kianersi said.
One possibility is that this increased risk is driven by night owls’ biology, or more specifically, the way that their internal body clocks deviate from their everyday schedules.
Other research has found that misalignment between someone’s circadian rhythm and their sleeping or eating schedule can negatively affect appetite-regulating hormones, glucose metabolism, and mood.
These changes in hormones make night owls more prone to insulin resistance and metabolic syndrome, Hatipoglu explained.
Night owls also tend to get less sleep during the work week and more on weekends, which could be a concern as irregular bedtimes have been associated with a higher risk of hypertension.
The study did find that diabetes risk was higher for night owl nurses who did not do shift work—meaning they likely had to work, at least to some degree, in the mornings. This could imply that if a person’s circadian rhythm, or body clock, is misaligned with their daily routine, it may worsen their health.
"The best scenario for our health is to follow our internal body clock,” said Kianersi. “If you are a night owl, you prefer to go to bed late at night—if you have work that syncs to your body clock, then that is healthy for us. But if you’re an early bird, then working late [at] night, it’s going to be a little bit hazardous.”
While the study raised questions regarding the link between evening chronotype and diabetes, limitations were in place:
Kianersi noted that since chronotype can actually be genetically determined, future studies will need to examine changes on the cellular level.
The new findings may seem alarming for people who prefer to go to bed and wake up later, however, there’s a silver lining—the lifestyle factors largely driving night owls’ increased diabetes risk can be changed.
“It is good news [for] night owls,” Kianersi said. “Even though they have an increased risk of diabetes, maybe if they just adjust some of their poor health habits, these increases can substantially be decreased.”
Rather than trying to become an early bird, a much simpler solution is for night owls to make small lifestyle adjustments in the six categories included in the study.
This would mean aiming to get at least 150 minutes of moderate-to-vigorous physical activity each week, eating a nutritious diet, getting between 7 and 9 hours of sleep each night, lowering tobacco and alcohol consumption, and keeping a healthy weight.
Reducing screen time and managing stress might also help people get better sleep and lower their health risks, Hatipoglu added.
Beyond the individual, big picture implications of this type of research could be a shift toward more personalized or flexible work hours, Kianersi said, so that early birds and night owls could have a schedule that better aligns with their internal clock.
