Individuals who prefer to stay up late and sleep late in the morning may be at a higher risk for chronic diseases such as type 2 diabetes and heart disease, according to a new study published in the journal Experimental Physiology.
The study, which dubs such individuals ‘night owls,’ found that people who fall into this category generally have bodies that are less able to burn fat for energy and tend to build up fat more easily. Those who wake early, on the other hand, use fat as an energy source more frequently and are typically more physically active during the course of a day.
So what does all of that mean?
Researchers say that night owls may have an increased risk of being impacted by type 2 diabetes and heart disease. But just because you prefer staying up at night doesn’t mean you’re guaranteed to have these health challenges.
According to lead study author Steven Malin, PhD, an associate professor of metabolism and endocrinology at Rutgers University, knowing your sleep preference is important because it helps to make decisions regarding a healthy lifestyle to promote a reduction in disease risk.
“My hope would be that these findings provide a physiologic rationale for why people may have heightened disease risk,” Malin told Health. “In turn, people can take necessary steps to engage in physical activity, eat a balanced diet throughout the day while avoiding late night eating, and try to be in bed earlier to promote alignment with the next day’s tasks so that people feel their best.”
Previous research has suggested that a person’s natural tendency to fall asleep and wake up at a certain time—which is known as their chronotype—influences multiple facets of one’s health from an increased risk of heart disease and psychiatric disorders, to influencing your risk for an early death.
All chronotypes fall on a spectrum and research suggests there might be up to six—with the most common being morning larks and night owls. Morning larks, or early birds, go to sleep early and wake earlier in the day. Night owls, meanwhile, are people who prefer staying active and awake at night and sleeping later in the morning.
People have these different chronotypes because everyone’s internal clock or circadian rhythm works a bit differently, Thomas Kilkenny, DO, the director of the Institute Sleep Medicine at Staten Island University Hospital, who was not affiliated with the study, explained.
Circadian rhythm works on a 24-hour cycle and is regulated by light and darkness. When sunlight enters the eyes, it stimulates a pea-shaped gland in the brain called the pineal gland to stop the production of a sleep hormone called melatonin. When night falls, melatonin is activated once again, promoting sleepiness.
“If you’re a natural early bird, your circadian rhythm decreases melatonin much earlier in the morning, resulting in increased activity [when] you awaken,” Dr. Kilkenny explained. “Night owls, however, have a body clock that secretes melatonin much later in the evening, resulting in delayed sleep and sluggish mornings.”
Importantly, one consistent trend throughout chronotype research to date has been that night owls tend to have poorer health outcomes overall—though there was little understanding of how a late chronotype resulted in an increased risk of chronic disease among such individuals.
Malin and his team thought they could provide some insight into this question.
Biological Differences Studied
The study reviewed the biological differences of 51 people with metabolic syndrome—conditions such as excess body fat and high blood pressure that raises the risk for heart disease, stroke, and diabetes. These individuals were divided into two groups based on questionnaires designed to measure early and late chronotypes.
The research team also used imaging to measure body mass and body composition. Other tests involved insulin sensitivity and breath samples to measure a person’s fat and carbohydrate metabolism at rest and during physical activity.
Participants were then monitored for a week with accelerometers on the right hip to keep track of when they were most active throughout the day. To minimize any dietary impacts or differences in the study, all participants ate a strict calorie and nutrition-restricted diet and fasted overnight.
In addition, participants undertook two 15-minute exercise sessions, one moderate and one high-intensity, on the treadmill. People’s aerobic fitness levels were measured through an incline challenge where the incline increased 2.5% every two minutes until the participant could not physically continue working out.
The results of the researcher’s efforts revealed that a person’s chronotype influences one’s metabolism. In other words, people categorized as early birds were more likely to convert more fat into energy compared to night owls. Night owls were more likely to use up less fat and more carbohydrates for energy during rest and exercise.
“Night owls may be more prone to heart disease and diabetes than early birds because their bodies are less able to burn fat for energy,” Dr. Kilkenny explained. He suggested that early birds probably burn through more fat because they are more active during the day, making them more likely to engage in exercise versus night owls who tend to be more sedentary.
While none of the participants were diagnosed with type 2 diabetes, night owls were more insulin-resistant (when the body does not respond well to insulin), needing more insulin to handle the metabolic needs of the body.
“This leads to obesity, weight gain, and abnormal lipid metabolism,” said Dr. Kilkenny. Early birds, on the other hand, were seen as insulin sensitive, where they had a better handle on managing blood glucose levels.
The cause of type 2 diabetes is not entirely clear, but Malin suggests insulin resistance is one of the main culprits. One explanation behind the link between insulin resistance and a late chronotype is that a 9-to-5 work schedule and other personal responsibilities are tailored more for an early bird rather than a late bird’s biological clock, causing stress that disrupts how their circadian rhythm naturally operates.
In other words, night owls “must still wake up to do a variety of things [like] take care of kids [and] get to work that may “force” them to be out of alignment with when they would still be sleeping. This changes their physiology and increases disease risk,” Malin explains.
Because people with late chronotypes had lower fitness levels and were less able to respond to insulin than early birds, Malin suggested that defects in the mitochondria (the powerhouse of the cell) make it harder to convert fat into energy and contribute to insulin resistance.
An alternative explanation, he said, is that a build-up of fat metabolites impair insulin activity in tissues like the muscles.
Research suggests chronotypes have a genetic component and might be passed down from your parents, making them difficult to change. But both experts say it’s not impossible—and there’s even some evidence that chronotypes change as we age.
Still, people who are late chronotypes and want to try and make a change are advised to take small and gradual steps toward shifting to being an early bird.
You may feel tempted to just go to bed earlier to wake up earlier, but it is not easy to fall asleep when one is not tired. Instead, Malin suggests going to bed 15 minutes earlier and waking up 15 minutes earlier.
“In time and depending on how things are going, this can expand another 15-minute window,” Malin said.
Additionally, Malin pointed out that a person can take advantage of the extra time to engage in light physical activity or even go outside in the sunlight to alert their circadian system.
Here are some additional steps both experts recommend to help reduce your risk of chronic disease regardless of one’s chronotype:
- Eating a low-carbohydrate or other balanced diet
- Doing daily aerobic exercises
- Break up sedentary behavior by moving around for 2 minutes every hour or taking 10-15 minute brisk walks after meals
- Avoiding stressful or vigorous activity late in the evening to prepare the body for sleep
- Minimizing stimulating foods (high sugar, caffeine), especially late at night
- Leaving electronics such as phones and tablets out of the bedroom
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