Night people are at higher risk of chronic disease, study finds

If you prefer to go to bed and wake up later — a sleep chronotype known as night owls — you may be at higher risk for type 2 diabetes and heart disease, according to a new study.

Night owls were more sedentary, had lower aerobic fitness levels, and burned less fat at rest and active than those first in the study.

Night owls were also more likely to be insulin resistant, meaning their muscles needed more insulin to get the energy they needed, according to the study published in the journal Experimental Physiology.

“Insulin tells the muscles to sponge and absorb glucose from the blood,” said study senior author Steven Malin, an associate professor in the department of kinesiology and health at Rutgers University in New Jersey.

“Think of it like tap water: you turn on the water and a drop touches the sponge and it’s immediately absorbed,” Malin said. “But if you’re not exercising, engaging those muscles, it’s like that sponge just sits there for a few days and it gets hard. A drop of water will not make it soft again.”

If sleep chronotype is affecting how our bodies use insulin and affecting metabolism, being a night person could be helpful in predicting a person’s risk for heart disease and type 2 diabetes, Malin added.

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

“There is good evidence that sleeping late is associated with an increased risk of metabolic and cardiovascular disease,” said Zee, who is also a professor of neurology.

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

All humans have a circadian rhythm — a 24-hour internal clock that regulates the release of the hormone melatonin to promote sleep and stops production for us to wake up.

Our biological clock also tells us when we get hungry, when we feel sluggish, and when we feel excited enough to exercise, among many other bodily functions.

Biological clock and chronotype

Traditionally, sunrise and sunset regulated the human sleep-wake cycle. Daylight enters the eyes, travels to the brain and triggers a signal that suppresses melatonin production. When the sun goes down, the biological clock reactivates the production of melatonin and, a few hours later, sleep arrives.

Your personal sleep chronotype, which is believed to be inherited, can alter this natural rhythm. If you’re an innate early riser, your circadian rhythm releases melatonin much earlier than normal, energizing you to become more active in the morning.

In night people, however, the body’s internal clock secretes melatonin much later, making mornings sluggish and pushing the peak of activity and alertness later and at night.

Sleep chronotype can have profound effects on productivity, school performance, social functioning and lifestyle habits, experts say.

Early risers tend to perform better in school and are more active throughout the day, which may partly explain why studies have found they have a lower risk of cardiovascular disease, Malin said.

Nocturnal types may be more risky, use more tobacco, alcohol, and caffeine, and are more likely to skip breakfast and eat more later in the day.

In addition, research suggests that “later chronotypes have greater body fat located more in the stomach or abdominal area, an area that many health professionals believe is worse for our health,” Malin said.

The researchers sorted 51 adults without heart disease or diabetes into morning or evening chronotypes, based on their natural sleep and wake preferences.

During the study, participants ate a controlled diet and fasted overnight, while their activity levels were monitored for a week.

Fat or carbohydrates?

The research team determined each person’s body mass, body composition and fitness level and measured insulin sensitivity levels. In addition, the researchers looked at how each person’s metabolism got most of its energy, whether from fat or carbohydrates.

“Fat metabolism is important because we think that if you can burn fat for energy, it will help the muscle take up glucose more lastingly,” Malin said.

Burning fat can promote stamina and more physical and mental activity throughout the day. Carbohydrates, on the other hand, are what the body uses for intense physical activity. Carbs are burned faster, which is why many athletes load up on carbs before a race or marathon.

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

More research is needed, Malin said, to confirm the findings and determine whether the metabolic differences are due to chronotype or a potential misalignment between a night person’s natural preference and the need to wake up early due to society’s established hours for work. and school.

People who are continually out of sync with their innate biological clock are said to be in “social jet lag”.

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