A difference of just 30 minutes between the time children go to bed on school nights and the time they go to bed on days off could have a negative impact on their waistlines and weight, a new study warns.
While it was already known that poor quality sleep can have undesirable health implications, this research complicates the situation by adding a factor to the equation that apparently flew under the radar until now.
"This study shows that staying up too late during the week has deleterious impacts, and the same thing on weekends, but especially if there is a big difference between those times," said Dr. Melanie Henderson, a pediatric endocrinologist at CHU Sainte-Justine.
The Finnish authors of this study conducted a longitudinal analysis of about 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 an additional 0.6 centimetres in waist circumference two-and-a-half years later.
While this may seem small, Dr. Henderson said, it's important to keep in mind that this is a "cumulative" effect that will lead to increased risk over time, especially since it will likely be associated with other things, such as eating habits.
In fact, those who get little sleep will experience what she calls "false hunger" and will tend to seek out rich, calorie-dense foods for energy, which can then lead to weight gain.
Those who get little sleep are also more likely to have more central adiposity, compared to more generalized adiposity, which can be particularly harmful to health, Dr. Henderson said. That could explain the increased waistline seen by the researchers.
AN HOUR OR TWO LATER
The researchers found, on average, that children went to bed an hour later on days off, compared to school days. However, one in eight children went to bed two hours later.
This delay before bedtime, and a later bedtime, was more common among youth who spent a lot of time on a screen.
"Based on our findings and those of other researchers, we hypothesize that inconsistency in bedtime and sleep time is likely due to screen time and socialization with peers," the authors reported in the Journal of Sleep Research.
This could lead to a "circadian disruption" that would interfere with metabolism, they added.
"Clinically, I very frequently see young people who have very late bedtimes because they're behind their screens playing video games or watching videos ... and it's curtailing sleep duration and sleep quality," Dr. Henderson said.
Teenagers going to bed at a "reasonable time" during the week, but much later on the weekend, will affect their sleep, "and we know that these effects have a propensity to have adverse health effects, including a greater risk of obesity," according to Dr. Henderson.
"What I explain to my patients is that if you go to bed at 10:30 on weeknights, but on Friday and then Saturday night you go to bed at 4 a.m., made it to Sunday night, it's like you went to Europe on the weekend for your body," she illustrated, agreeing with the Finnish researchers.
Further analysis showed the researchers that the association between bedtime and increased body weight was one-way: children with fluctuating bedtimes had increased weight, but a genetic predisposition to increased body weight did not appear to be responsible for the delay in going to bed.
On a biological level, the study stateds, previous studies have shown that later bedtime is associated with poorer sleep quality. In particular, the sleep cycle during which the body repairs and grows could be missing.
"It's a reminder to parents that kids shouldn't be going to bed late on weekdays, or on weekends," Dr. Henderson concluded.
"We shouldn't have big lags. Kids who chronically have a very late bedtime during the week and much later on the weekend, it's brittle in terms of their sleep quality, their sleep duration as well, and over the long haul, what we're seeing is that it has significant and persistent impacts over time."
This report by The Canadian Press was first published in French on April 25, 2023.
