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If you prefer to go to bed and wake up later — a sleep chronotype known as the night owl — you may be at higher risk for type 2 diabetes and heart disease, according to a new study.
The night owls were more sedentary, had lower aerobic fitness levels, and burned less fat at rest and in activity than the early birds 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 Monday in the journal Experimental Physiology.
“Insulin tells the muscles to be a sponge and to absorb the glucose from the blood,” said the study’s lead author, Steven Malin, an associate professor in the Department of Kinesiology and Health. at Rutgers University in New Jersey.
“Think of it like water from a water tap: you turn on the water and a drop hits the sponge and is immediately absorbed,” Malin said. “But if you don’t exercise, don’t engage those muscles, it’s like that sponge has to sit for a few days and become rock hard. A drop of water isn’t going to soften it at new.
If sleep chronotype affects how our bodies use insulin and impacts metabolism, then being a night owl could be useful in predicting the risk of heart disease and type 2 diabetes, Malin added.
“The study adds to what we know,” said Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg School of Medicine in Chicago, who was not involved in the research.
“There is good evidence that being a late sleeper has been linked to a higher risk of metabolic and cardiovascular disease,” said Zee, who is also a professor of neurology. “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, all of which have been shown to affect insulin sensitivity. .”
All humans have a circadian rhythm – an internal 24-hour clock that regulates the release of the hormone melatonin to promote sleep and shuts down production so we wake up. Our biological clock also determines when we are hungry, when we feel sluggish, and when we feel energized enough to exercise, among many other bodily functions.
Traditionally, dawn and dusk regulated the human sleep-wake cycle. Daylight enters the eyes, travels to the brain and triggers a signal that suppresses the production of melatonin. When the sun goes down, the biological clock restarts the production of melatonin and, a few hours later, sleep arrives.
Your personal sleep chronotype, thought to be inherited, can alter this natural rhythm. If you’re an innate early riser, your circadian rhythm releases melatonin much earlier than normal, giving you the energy to become more active in the morning. In night owls, however, the internal biological clock secretes melatonin much later, which slows the early mornings and pushes peak activity and alertness later in the afternoon and evening.
According to experts, sleep chronotype can have profound effects on productivity, academic performance, social functioning, and lifestyle habits. Early risers tend to perform better in school and are more active throughout the day, which may partly explain why studies have shown they have a lower 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. Additionally, research suggests that “later cronotypes have higher body fat located more in the stomach or abdominal region, an area that many medical professionals believe is worse for our health,” Malin said.
The researchers classified 51 adults without heart disease or diabetes into morning or evening chronotypes, based on their natural sleep and wake preferences. During the study, participants followed a controlled diet and fasted overnight while their activity levels were monitored for a week.
The research team determined each person’s body mass, body composition and fitness level, as well as measured levels of insulin sensitivity. Additionally, the researchers looked at how each person’s metabolism gets most of its energy, either from fat or carbohydrates.
“Fat metabolism is important because we believe that if you can burn fat for energy, it will help muscle take up glucose more sustainably,” Malin said.
Burning fat can promote endurance 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 consume carbs before a race or marathon.
The test results showed that the early birds used more fat for energy at rest and during exercise than the night birds in the study, which used more carbohydrates as a fuel source.
More research is needed, Malin said, to confirm the results and determine whether the metabolic differences are due to chronotype or a potential mismatch between a night owl’s natural preference and the need to wake up early due to hours. set by society for work and school.
People who are continually out of sync with their innate biological clock are said to be “social jet lag.”
“It goes beyond diabetes or heart disease,” Malin said. “It may indicate a larger societal problem. How do we help people who may be out of alignment? Are we, as a society, forcing people to behave in ways that might actually put them at risk?