Kids who stay up later on weekends are more likely to be fat as scientists blame ‘social jet lag’
- The study of children in Finland found that going to bed later led to larger waistlines
- Researchers say “social jet lag” may affect how efficiently they process food
Letting school kids stay up a little longer on weekends may seem like an innocent treat.
But children whose bedtimes are later on weekends than during the week tend to be heavier, with larger waistlines, a study suggests.
That’s likely due to “social jet lag” — the shift in a person’s biological clock caused by fluctuating bedtimes, which can also affect how efficiently they process food.
Researchers looked at 10,245 children aged nine to 12 in Finland who were asked what time they went to bed on school nights and non-school nights.
Research shows that an average child whose bedtime was two hours later would have a body mass index (BMI) 0.32 higher than children with consistent bedtimes
The results show that the average child who goes to bed two hours later on weekends has a waist circumference that is approximately 2.4 centimeters larger.
This was based on a 148 cm tall child.
An average child whose bedtime was two hours later would have a body mass index (BMI) 0.32 higher than children with a consistent bedtime, the results suggest.
Dr. Sohvi Lommi, co-author of the study from the Folkhälsan Research Center in Finland, said: ‘Parents should pay attention to bedtimes and try to maintain a regular routine on weekends.
“These results suggest that children may gain weight if their bedtime moves too much.”
The study authors conclude: ‘Promoting early bedtime, especially on weekends, should be considered in the prevention of obesity in school-aged children.’
They add: ‘Consistent bedtimes between non-school days and school days can be achieved in two ways: either by allowing later school start times or by aiming for earlier bedtimes on non-school days.
“Of these, the first seems more feasible for adolescents and their families.”
About one in eight children go to bed at least two hours later on weekends, the new study finds.
That probably means sleeping later the next day, without a screaming parent or alarm clock waking them up.
Experts believe that this difference in sleep and wake times messes with a person’s internal biological clock – what is called social jet lag because it feels a bit like jet lag from flying to a country with a different time zone.
The new study provides evidence to support the idea that social jet lag causes people to gain weight, because children who go to bed later on weekends had higher BMI, standardized for their age and gender, and higher waist circumference for their height.
Of the 10,245 children surveyed who took part in the Finnish study of teen health, about half provided more information two and a half years later, when their parents measured their weight, height and waist circumference again.
At the time, going to bed two hours later on weekends at age 11 was linked to a waistline nearly a quarter of an inch (0.6 cm) larger than children with consistent bedtimes.
Bedtimes that jumped back and forth were linked to higher weight and larger waistlines in children, regardless of how long they slept.
The average child in the study went to bed at 9:30 p.m. on a school night and at 10:30 p.m. on a non-school night.
The study found that children who spent more time in front of television and computer screens slept longer on weekends.
However, the researchers note that children self-reported their bedtimes, which may have made them inaccurate, and that bedtimes may have changed over time.
The study, published in the Journal of Sleep Research, was reported by New scientist magazine.