An alarming percentage of American children aren’t getting enough sleep, and these kids are more likely to be overweight or obese. But why? Why is there a connection between sleep loss and weight gain? Experiments suggest the answer has to do with the way sleep restriction makes us feel about food: Images of food trigger more activity in the reward centers of the sleep-restricted brain. And tired kids may switch into “sugar mode” — increasing their consumption of sweetened drinks and other foods that raise blood glucose levels quickly.
According to parental surveys, approximately 35% of kids in the United States are what researchers call “short sleepers” — individuals who sleep less than the recommended amount (Wheaton et al 2021). According to self-reports, the numbers are even higher for teens. In one recent study, nearly 73% of U.S. high school students said they were sleeping less than 8 hours per night. Experts believe that most teens should sleep at least 8-10 hours (Wheaton et al 2018).
Things aren’t this bad everywhere around the world, but short sleep among teenagers isn’t uncommon. In many European countries, at least one-third of all adolescents are sleeping less than the recommended amount on school nights (Gariepy et al 2020). And for kids skimping on sleep — wherever they might live — there’s reason for concern. As I note elsewhere, restricted sleep is linked with a variety of cognitive and emotional problems, as well as health risks. Health risks that include a tendency to consume more sweets, and to gain excess weight.
But what exactly do we know about food, sleep loss, and weight gain in children? Are kids at risk from an early age? Do we have reason to conclude that sleep loss causes unhealthful eating, weight gain, or obesity? Do researchers understand how short sleep might contribute to these problematic outcomes? And what can we do to protect kids?
Here’s a review of the evidence, and some advice for improving your child’s sleep.
Short sleep is linked with childhood obesity.
Decades of research has confirmed same pattern. Short sleepers are more likely to be overweight or obese.
It’s true across different age groups — from infancy to adolescence to adulthood (Deng et al 2021). It’s also true across cultures. In the United States, United Kingdom, and Canada, kids from a variety of ethnic backgrounds conform to the trend (Chehal et al 2022; Collings 2021; Zhang et al 2021). So do kids in China (Guo et al 2021), South Africa (Rae et al 2021), and Brazil (Halal et al 2016).
How big is the effect? It’s hard to say, and it probably depends on lots of additional factors. But in one meta-analysis of published studies, researchers found that the risk of being either overweight or obese was 21% lower for every hour per day that a child sleeps (Ruan et al 2015). In another meta-analysis, researchers estimated that short sleepers were anywhere between 30% and 220% more likely to end up overweight or obese (Miller et al 2018).
Short sleep has also been linked with distinctive patterns of eating.
For example, consider a study of more than 1300 British children under the age of two. Among these toddlers, sleeping less than 10 hours per day was associated with a higher total intake of calories. Compared to kids who slept between 11 and 12 hours, short sleepers consumed an average of 50 additional calories each day (Fisher et al 2014).
Other studies — targeting Danish school children between the ages of 8 and 11 — have found that short sleepers tend to derive more calories from energy-dense foods, including sweetened drinks and foods with added sugar (Kjeldsen et al 2014; Hjorth et al 2014).
Of course, all of the data we’ve discussed so far concern correlations only. The studies can’t tell us why short sleep is linked with obesity, or with an increased intake of sweets. Maybe there are medical conditions that puts kids at risk for both short sleep and obesity, in which case we shouldn’t assume that sleeping less causes dietary changes or weight gain.
To establish causation, we need experiments. And thankfully, we have some.
Experimental evidence: Short sleep makes teenagers seek out foods that raise blood sugar quickly.
How can we use experiments to pinpoint causation? What’s needed is a way to test the effects of different sleep schedules, while holding other factors constant. Then you can see if kids respond differently to food depending on the amount of time they are permitted to sleep.
Dean Beebe and his colleagues pioneered this approach. Back in 2013, they recruited 41 teenagers, and fitted them with wrist actigraphs (devices that provide objective estimates of sleep duration). For seven days, the kids went about their usual daily lives, and Beebe’s team collected data on their natural sleep tendencies. On average, these teens were sleeping just 7 hours per day. They were habitual short sleepers!
Next came the experimental manipulation. Each teenager was assigned to experience one of two, special sleep schedules:
- The restricted schedule permitted kids to spend only 6.5 hours in bed each night.
- The healthy sleep schedule required kids to spend 10 hours in bed each night.
The teens continued to sleep with actigraphs, so the researchers could be sure that these schedules resulted in substantial differences between groups. Kids on the healthy sleep schedule got an average of 2.5 more hours of sleep each night — a pretty big difference.
The schedules continued for five days, Monday through Friday. On Day 6 — Saturday — kids reported on everything they had eaten over the past 24 hours. Then, after a couple of nights without regimented sleep rules, the kids continued the experiment, switching over to whichever sleep schedule they hadn’t yet experienced. For instance, teens who had just finished the restricted schedule began the healthy schedule, and vice versa. After 5 days, kids completed a second, final, diet inventory.
How did things turn out? The teens had continued to sleep with wrist actigraphs, so the researchers were able to confirm that total sleep duration varied by experimental condition. When kids were on the “healthy sleep” schedule, they got an average of 8.9 hours each night. By contrast, kids averaged on 6.3 hours on the restricted schedule.
And it seems to have made a difference in diet. It wasn’t so much that kids consumed more calories when they were sleep-restricted. What was more notable was that their food choices shifted. Under conditions of short sleep, kids ate more sweets and desserts (Beebe et al 2013).
A follow-up study reported similar results (Simon et al 2015). And — more recently — researchers conducted an experiment that examined the timing of snacks.
In this study of 93 adolescents, the team didn’t just confirm that sleep-restricted kids ate more carbs, added sugars, sweetened drinks, and other foods that raise blood sugar quickly. They also noticed a trend for nighttime consumption: Kids tended to eat these foods after 9pm (Duraccio, Whitacre et al 2021).
As lead author Kara Duraccio explained in an interview at Brigham Young University:
“We suspect that tired teens are looking for quick bursts of energy to keep them going until they can go to bed, so they’re seeking out foods that are high in carbs and added sugars.”
It’s not an irrational strategy, if you need to stay up late doing your school work. But it’s not a healthful strategy.
Studies also suggest that short sleep makes us feel more rewarded by eating food.
Once again, the evidence comes from experimental studies, where researchers randomly assign people to different sleep schedules, and then test for changes in each volunteer’s responses toward food.
In some studies, these tests have included brain scans, and the results have been consistent in both adults and adolescents. Restrict sleep (for example, to just 5 hours per night for a teenager), and the brain responds differently to images of food. Parts of the brain associated with processing rewards become more active (Demos et al 2017; Jensen et al 2019; St-Onge et al 2014).
Other studies have focused on adolescent’s conscious testimony about food. Randomly assign kids to different sleep schedules, and it can change the way they rate different foods. Under conditions of sleep restriction, they judge images of food as more appealing (Duraccio, Krietsch et al 2019; Duraccio et al 2021; Simon et al 2015).
Does sleep restriction trigger hormonal changes that make kids feel hungrier? That isn’t clear.
In some experimental studies on adults, researchers have observed that sleep restriction is associated with a surge in ghrelin, a hormone that stimulates the appetite (e.g., Broussard et al 2016; Lin 2020). But it’s not clear that this always happens (Soltanieh et al 2021; Zhu et al 2019), or that the effect extends to kids (Hart et al 2013; Chaput and St-Onge 2014). So although short sleep influences the way we respond to food, we can’t be sure that this is because hormonal changes are making us feel hungrier. It might simply be that we find food more enjoyable (Chaput end St-Onge 2014).
What about the stress hormone, cortisol? Doesn’t sleep restriction impact body weight by increasing cortisol levels?
I’ve seen these claims in the popular media, but I haven’t found any research in support of the idea that sleep restriction causes weight gain children via elevated cortisol levels. In a recent study, researchers tracked the development of more than 360 children from infancy. They monitored changes in sleep duration, body mass index, and cortisol levels in kids over time. Sleep duration was linked with body mass index. But cortisol levels were unrelated to this link (Marceau et al 2019).
Given the evidence that short sleep can alter a child’s eating behavior — and perhaps lead to excessive weight gain — what can we do about it?
We’ve learned that short sleep may intensify a child’s interest in sugary snacks and drinks, so it makes sense to be vigilant when it comes to these foods. We should also pay attention to nighttime eating. As Kara Duraccio’s team discovered, this is when sleep-deprived teens tend to seek out foods with high glycemic loads.
But the most important thing is to address your child’s sleep loss. As I explain elsewhere, short sleep has all sorts of negative consequences for a child’s health and well-being. Excessive weight gain is just one of them. Here are some tips for investigating — and improving — your child’s sleep habits.
1. Look for signs that your child isn’t getting enough sleep.
For guidelines, see my Parenting Science article, “Signs of sleep deprivation in children and teens.”
2. Troubleshoot for biological, environmental, and psychological problems that make it hard for your child to fall asleep at night.
See my article, “Bedtime problems: Solutions for the science-minded.”
3. Watch out for nighttime screen use.
The evidence is building — a lot of kids aren’t getting enough sleep at night because they use phones, computers, and other devices before bedtime. Or even after bedtime. Learn more about the ways that these devices undermine sleep here.
4. Consider making rescheduling your child’s bedtime.
Is your child in the habit of falling asleep late? Research suggests that late bedtimes are themselves a risk factor for consuming high glycemic index foods (Duraccio et al 2021) and for becoming overweight or obese (Grummon et al 2021). So it can be a good idea to reschedule your child’s habitual bedtime to an earlier part of the evening. For help with this, check out my article on “bedtime fading” — an evidence-based technique for ensuring that your child will accept the change.
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image of children’s hands reaching for donuts by ulkas / istock
image of teen eating candy bar by IanaChyrva / istock
Content last modified 1/14/2022