(Montreal) A difference of just thirty minutes between the time children go to bed on school evenings and the time they go to bed on holidays could have a negative influence on their waist circumference and their weight, warns a new study.

If we already knew that poor quality sleep can have undesirable repercussions on health, this research complicates the situation by adding to the equation a factor that has apparently gone under the radar until now.

“This study shows that going to bed too late during the week has deleterious impacts, and the same thing on weekends, but especially if there is a big difference between these hours,” summarized Dr. Mélanie Henderson, who is a pediatrician. endocrinologist at CHU Sainte-Justine.

The Finnish authors of this study carried out a longitudinal analysis of approximately 5,000 children aged 9 to 12 years. They found that later bedtime on days off – and fluctuations in bedtime – at age 11 were associated with adding 0.6 centimeters to waist circumference two and a half years later.

While this may seem modest, said Dr. Henderson, it should be kept in mind that this is a “cumulative” effect that will lead to increased risk over time, especially as it will be probably associated with other elements, such as eating habits.

In fact, she says, those who sleep poorly will experience what she calls “false hunger” and will tend to seek out calorie-dense, high-calorie foods for energy, which can then lead to weight.

Those who sleep little are also more likely to have more central adiposity — compared to more generalized adiposity — which can be particularly harmful to health, Dr. Henderson said. This could explain the increased waist circumference seen by Finnish researchers.

Researchers found, on average, that children went to bed an hour later on days off compared to school days. One in eight children, however, went to bed two hours later.

This delay before going to bed, and a later bedtime, was more common among young people who spent a lot of time on a screen.

“Based on our findings and those of other researchers, we hypothesize that the lack of consistency in bedtime and sleep times is likely due to screen time and peer socialization,” report so the authors in the Journal of Sleep Research.

This could lead to a “circadian dysregulation” that interferes with metabolism, they add.

“Clinically, I very frequently see young people who have very late bedtimes because they are behind their screens playing video games or watching videos […] and it interferes with the duration of sleep and the quality of sleep. sleep,” Dr. Henderson confirmed.

For teenagers to go to bed at a “reasonable time” during the week, but much later on the weekend, will have an effect on their sleep, “and we know that these effects have a propensity to have harmful effects health, including a greater risk of obesity,” Dr. Henderson said.

“What I explain to my patients is that if you go to bed at 10:30 a.m. on weeknights, but on Friday and then Saturday night you go to bed at 4:00 a.m., by Sunday night, that It’s like you went to Europe over the weekend for your body,” she said, agreeing with the Finnish researchers.

Further analysis showed the researchers that the association between bedtime and greater adiposity was one-sided: children with fluctuating bedtimes had greater adiposity, but a genetic predisposition to adiposity. more important did not seem to be responsible for the delay before going to bed.

Moreover, on a biological level, can we read in the study, previous studies have shown that a later bedtime is associated with poorer quality sleep. In particular, the sleep cycle during which the body repairs and grows could be absent.

“It reminds parents that kids shouldn’t go to bed late in the week or on weekends,” Dr. Henderson said. There shouldn’t be any big delays. Young people who chronically have a very late bedtime during the week and much later on weekends, it interferes with the quality of their sleep, the duration of their sleep too, and in the long term, what we see, is that it has significant and persistent impacts over time. »