Why does staying up late on the weekends lead to weight gain in kids?

It’s the weekend! Your kids don’t have to get up for school in the morning, so why not let them stay up for an extra hour or two watching a movie tonight? Perhaps it is family game night and that Monopoly game lasts forever…

Parents know that childhood obesity is on the rise. And any parent with a child who is slightly heavier than the norm also knows that they will get a long lecture from the pediatrician at their next well-check visit. The pediatrician will probably suggest that your child should cut out the sugary drinks (it’s all soda’s fault!) or spend an extra 30 minutes being active (sign the kids up for soccer!).

While recommendations to cut out the soda or make your kids exercise more are well intended, scientific research points to another cause that is often overlooked.

It turns out that staying up an hour or more past normal bedtime on the weekends is linked to about 1 BMI point greater weight gain in children ages 5-11. (The impact on adults is a whopping 330% increase in the risk of obesity – but that is a whole ‘nother article for another day…)

A new article out this week in the journal Global Pediatric Health gives us a glimpse into the impact of a new study on ‘social jetlag’ and childhood obesity. The article explains that social jetlag is the term applied to staying up late on the weekends. For example, you might normally go to bed around 10 pm and get up at 6 am during the week to go to work.  On the weekends, that might shift so that you go to bed after midnight and then sleep in the next morning. Typical behavior in our modern society, and one that no one really thinks about or questions. But the chronic shifting of your circadian rhythm every weekend is hard on your body – similar to flying several time zones away and having jetlag.

The study was conducted with 341 children in New Zealand. The results showed that an hour (or more) later bedtime on the weekends was associated with a 3% increase in body fat and a BMI increase of 0.9 kg/m2.  And this was with almost all of the study participants still getting 9+ hours of sleep.  The change in bedtime on the weekends was made up for by sleeping late the next morning.

You may be wondering why on earth staying up an hour or two later every weekend would make any difference in weight.  A normal assumption would be that the kids are staying up late eating junk food, but the link between weight gain and social jetlag doesn’t seem to involve the number of calories eaten.  Animal studies that keep the calories constant find that fat mass increases when the animal is exposed to light at the wrong time. One reason for this is a decrease in energy expenditure due to a change in the sympathetic nervous system.(study) Another reason is that the changes in the circadian clock gene transcription increase weight gain. (study)  (study)

Let’s put this into context.  The usual recommendation is to cut back on sugary drinks, and we often assume that diet is at the root of all weight problems. It’s a normal assumption, and, of course, diet plays a role in obesity. But the headlines about sugar and the taxes on sugary drinks may be missing the mark. Sugar consumption is actually down… it peaked in the late 90s and is down about 20% since then – while obesity is still rising. (source)  Don’t get me wrong, here. I’m not saying you should be pumping your kids full of sugary drinks.  Just that the media hype is such that we often think the only reason for childhood obesity.

 

So how does sugary soda compare to social jet lag when it comes to childhood obesity?  An 18-month study of almost 500 children looked at the effect of replacing one 250-ml sugary drink with a sugar-free drink every day. The sugary beverage contained 26g of sugar and 104 calories. Replacing that with the sugar-free beverage caused that group of children to gain .9kg less over the course of 18 months (keep in mind these are growing kids). While there weren’t the same BMI measurements as in the social jetlag study, the sugary beverage study didn’t show a great deal of difference 1lb (.9kg) wouldn’t equal almost a whole BMI point in kids.  Not quite apples to apples, but indicative that eliminating social jetlag would be more impactful (in terms of BMI) than eliminating a soda per day.  (Yes, there are other reasons to cut out soda – so don’t take this as a reason to go out and buy the kiddos a Big Gulp.)

The solution isn’t cutting edge or costly. It is simply to keep to a routine bedtime both during the week and on the weekends.

While the study doesn’t go into all of the aspects of the impact of light at night on kids and their sleep, there are many other studies that successfully make the case for eliminating blue light at night (TV, laptop, phones, and overhead lights). Apps that reduce the amount of blue light are not enough to protect kids from the melatonin suppressing effects. If you can’t pry the iPad out of their hands in the evening, try some blue light blocking glasses that are made for kids. You are looking for ones with orange or red lenses that block 100% of the blue light. Here is one example and another example:

If your kids are ok with eliminating electronics at night, you can reduce the overall amount of blue light by simply switching off your bright overhead lights and turning on lamps with antique bulbs.  There are so many options these days for cool looking light bulbs that cast a warm orange glow. Amazon has dozens of options, and Lowe’s carries a bunch as well.

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