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If you prefer to go to bed later and get up later – a sleep chronotype known as a night owl – you may be at a higher risk of type 2 diabetes and heart disease, a new study has found.
Night owls were more sedentary, had lower aerobic fitness levels, and burned less fat at rest and during 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 need, according to research published Monday in the journal Experimental Physiology.
“Insulin tells the muscles to act as a sponge and absorb glucose from the blood,” said lead study 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 faucet: you turn on the water and a drop hits the sponge and is immediately absorbed,” Malin said. “But if you’re not exercising, shrinking those muscles, it’s like that sponge sits for a couple of days and gets hard. A drop of water will not soften it again.’
If sleep chronotype affects how our body uses insulin and metabolism, being a night owl could be useful in predicting a person’s 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 study.
“There is good evidence that late sleep has been associated with an increased 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 exposure to less morning light and more evening light affect insulin sensitivity.”
All humans have a circadian rhythm: an internal 24-hour body clock that regulates the release of the hormone melatonin, which induces sleep and stops production, so that we wake up. Our body clock also directs when we’re hungry, when we feel sluggish, and when we’re motivated enough to exercise, among many other bodily functions.
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 body clock turns melatonin production back on, leading to sleep a few hours later.
Your personal sleep chronotype, which is thought to be inherited, can alter this natural rhythm. If you’re a born preemie, your circadian rhythm releases melatonin much earlier than normal, energizing you to be most active in the morning. In night owls, however, the internal body clock secretes melatonin much later, making the early mornings sluggish and encouraging peak activity and alertness in the late afternoon and evening.
Sleep chronotype can have significant effects on productivity, school performance, social functioning and lifestyle habits, experts say. Early risers perform better in school and are more active during the day, which may partly explain why studies have found they have a lower risk of cardiovascular disease, Malin said.
Evening types may take more risks, consume more tobacco, alcohol and caffeine, and are more likely to skip breakfast and eat more during the day. In addition, studies suggest that “later chronotypes have more body fat located more in the stomach or abdomen, an area that many health professionals believe is worse for our health,” said Malin.
The researchers classified 51 adults without heart disease or diabetes into either morning or evening chronotypes based on their sleep and wake preferences. During the study, participants ate a controlled diet and fasted overnight while their activity levels were monitored for a week.
The research team determined measured each person’s body mass, body composition and fitness level, and insulin sensitivity level. In addition, the researchers looked at how each person’s metabolism got most of their energy, whether from fat or carbohydrates.
“Fat metabolism is important because we think you can burn fat for energy, which will help your muscles 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. Carbohydrates burn faster, which is why many athletes carb-load before a race or marathon.
The test results showed that the early birds used more fat for energy both at rest and during exercise than the night owls, which 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 a potential mismatch between chronotype, or the night owl’s natural preference, and the need to wake up early due to societally imposed hours. work and school
People who are constantly out of sync with their natural body clock are said to be in “social jet lag.”
“This extends beyond diabetes or heart disease,” Malin said. “It can indicate a larger social problem. How are we helping people who may be disadvantaged? Are we as a society forcing behavior that can put people at risk?