A new study has raised the alarm for night owls, suggesting those who get up and go to bed later could face a greater risk of Type 2 diabetes and heart disease.
The research from scientists in the US found that early risers tended to be healthier than those with more nocturnal habits, even when both groups exercised the same.
Differences in metabolism, particularly in relation to how the body deals with fat, are thought to be behind the divergence between early chronotypes (people who get up early) and late chronotypes (those who sleep late).
"These findings suggest that early chronotypes have differences in fuel selection that associate with Type 2 diabetes risk," the researchers wrote in the study, which was published in the journal Experimental Physiology on Monday.
The findings may be particularly relevant in the Middle East, where many people socialise late into the night and take a nap during the day.
Early bird benefits
A central finding of the study, which was based on the analysis of 51 participants, was that the bodies of early risers tended to use up more fat during rest and while exercising, even when both groups had the same level of fitness.
In addition, early risers were more physically active throughout the day, something likely to contribute to better health outcomes.
The researchers, from Rutgers University and the University of Virginia, found that late risers were more insulin-insensitive. This means their cells need more insulin, something the scientists said stemmed from differences in activity levels.
This could be associated with an increased risk of Type 2 diabetes, which is a major problem in the UAE and other parts of the Gulf region.
Eating later in the day and experiencing less light in the morning, and more darkness in the evening, have been suggested by experts as possible reasons why late sleepers may be more prone to insulin insensitivity.
Wake-up call
While the latest study indicates benefits to being an early riser, Dr Chen Song, a lecturer in neuroscience at Cardiff University in the UK who researches sleep, said it was not known overall whether it was better to be an early chronotype or a late chronotype.
One reason why a person’s sleep pattern may affect their well-being, she said, was a mismatch between the several factors, including physiological and cognitive (brain) influences, that affect how someone sleeps.
"This could be due to habits they developed during childhood, when they were forced to sleep early or late, which may influence later habits in life," she said.
Genetics influence a person’s sleep pattern, which is affected heavily by melatonin. This is a hormone released by the pineal gland, a pea-shaped structure in the brain.
Melatonin is sometimes called the hormone of darkness, because it is released in response to low light levels and acts on receptors in the body to cause people to go to sleep.
In early birds, melatonin is released earlier. This causes such people to go to bed and get up earlier and to be more active in the mornings.
By contrast, it is released later in night owls, who tend to stay up late and struggle with early starts. They are also said to be more likely to consume alcohol and caffeine and to have larger amounts of fat around the stomach and abdomen.
UK study raises concerns for late starters
The new research is not the first to indicate that being a night owl can have negative effects on health.
A study published last year that used data from wrist-activity monitors worn by more than 85,000 people in the UK found that, among those who stayed up late, there was a greater likelihood of self-reported anxiety or depression.
Speaking when that study was released, Dr Kristen Knutson, an associate professor who specialises in sleep medicine at Northwestern University Feinberg School of Medicine in the US, said health problems linked from being a late chronotype person were "likely a result of being a night owl living in a morning person's world". This, she said, could disrupt the body’s circadian or daily rhythms.
Highlighting the importance of not disrupting a person’s natural sleep patterns, the American Academy of Paediatrics has urged middle and high schools in the US to consider introducing later start times.
Starting later, the organisation said in a 2014 paper in the journal Paediatrics, tied in better with the body clocks of adolescents, who typically need between eight-and-a-half and nine-and-a-half hours of sleep a day.
