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If you prefer late nights to early mornings, you need to know what you’re risking…

A new study found that “night owls” (those who prefer to go to bed and get up later), may be at higher risk for type 2 diabetes and heart disease.

According to the study published in Experimental Physiology, night owls were more sedentary, had lower aerobic fitness levels, and burned less fat at rest while active than early birds. Night owls were also more likely to be insulin-resistant, meaning their muscles required more insulin to get the energy they need.

“Insulin tells the muscles to be a sponge and absorb the glucose in the blood,” said senior study author Steven Malin, an associate professor in the department of kinesiology and health at Rutgers University in New Jersey. “Think about it like water from a water faucet: You turn the water on, and a drop touches the sponge and is immediately absorbed,” Malin said. “But if you’re not exercising, engaging those muscles, it’s like if that sponge was to sit for a couple days and get rock hard. A drop of water isn’t going to make it soft again.”

If sleep chronotype is affecting how our bodies use insulin and impacting metabolism. In that case, Malin added, being a night owl might help predict a person’s risk for heart disease and type 2 diabetes.

“The study adds to what we know,” said Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine and professor of neurology at Northwestern University Feinberg School of Medicine in Chicago. She was not involved with the research.

“There is good evidence that being a late sleeper has been linked to a higher risk for metabolic and cardiovascular disease,” said Zee. 

 “Several mechanisms have been proposed: sleep loss, circadian misalignment, eating later in the day and being exposed to less morning light and more evening light, which have all been shown to affect insulin sensitivity.”

And another study shows that recovering from a lack of sleep takes longer than you might think.

Mammals have a circadian rhythm – rhythms are physical, mental, and behavioral changes that follow a 24-hour cycle. This internal clock also informs when we get hungry, feel the most sluggish, and feel energetic enough to exercise, among other things.

The study found that being a night owl may lower activity levels during the day.

Conventionally, sunrise and nightfall regulate the human sleep-wake cycle. As the daylight enters the eyes, it travels to the brain and sets off a signal that curbs melatonin production. When the sun goes down, the body clock turns melatonin production back on, which signals it’s time for sleep.

Your personal sleep chronotype, thought to be inherited, may alter your natural rhythm. For example, if you’re an early bird, your circadian rhythm releases melatonin much earlier, making you most active in the morning. On the contrary, if you’re a night owl, your internal body clock releases melatonin much later, pushing peak activity and alertness later into the afternoon and evening.

Experts say that sleep chronotype can profoundly affect productivity, school performance, social functioning, and lifestyle habits. For example, among university students, early birds perform better in school and are more active throughout the day. This may partly explain why studies have found they have less risk of cardiovascular disease, Malin said.

Evening types may take more risks, use more tobacco, alcohol, and caffeine, and are more likely to skip breakfast and eat later in the day. Research also suggests “later chronotypes have higher body fat located more in the stomach or abdominal region, an area which many health professionals believe to be worse for our health,” Malin said.

Researchers categorized 51 adults without heart disease or diabetes into morning or evening chronotypes based on their natural sleep and wake preferences. The participants activity levels were monitored while they ate a controlled diet and fasted overnight for a week.

The research team determined each person’s body mass, body composition, fitness level, and measured levels of insulin sensitivity. They also observed how each person’s metabolism acquired most of their energy via fat or carbohydrates.

“Fat metabolism is important because we think if you can burn fat for energy, that’s going to help the muscle pick up the glucose in a more enduring fashion,” Malin said.

Burning fat can promote endurance and better physical and mental activity throughout the day. On the other hand, the body uses carbohydrates for intense physical activity. As a result, carbs are burned more quickly, which is why many athletes carb-load before a race or marathon.

Test results showed early birds used more fat for energy at rest and during exercise than night owls in the study, who used more carbohydrates as a fuel source.

Malin said more research is needed to confirm the findings and determine if the metabolic differences are due to the chronotype or a potential misalignment between a night owl’s natural preference and the need to wake early due to the hours set by society for work and school.

People who are continuously out of synch with their innate body clock are in “social jet lag.” 

It’s a real thing. 

“This extends beyond just diabetes or just heart disease,” Malin said. “It may point to a bigger societal issue. How are we helping people who may be in misalignment? Are we as a society forcing people to behave in ways that might actually be putting them at risk?”


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