Do you sleep enough to banish unpleasant moods?

You might be happier if you got more sleep. That’s the finding of a large, new study conducted in kids across the United States.

Scientists have done a lot of research on sleep. They’ve shown that shortchanging your shuteye can lead to both weight gain and poor performance in school. Might it also mess with your moods or how you behave? An international team of scientists based in Shanghai, China decided to investigate.

To do that, they tapped into data from what’s known as the ABCD Study. Those initials stand for Adolescent Brain Cognitive Development. Begun in 2015, this study plans to follow more than 10,000 U.S. kids into adulthood. All were 9 to 10 years old when they started taking part. 

At regular intervals, ABCD researchers have been collecting records from parents on how much their kids sleep. The scientists also have been surveying the kids for signs of mood and behavior problems. For instance, they’re looking at whether a kid might have a habit of getting into fights or breaking rules. They even note whether students have trouble paying attention. 

Wei Cheng is a mathematician at Fudan University in Shanghai, China. He teamed up with other researchers across that city (some of whom also work at the University of Warwick in England). They pored over the ABCD data, comparing sleep records with emotional and behavioral findings. 

Kids who on average slept less than 7 hours a night were more likely to have behavior problems than kids who slept more, Cheng’s group found. Students who shortchanged their sleep scored 53 percent worse in the behavioral areas than kids who slept close to the recommended 9 or 10 hours per night. 

Kids who missed out on sleep also had more mood problems, including depression. Feeling sad or blue for longer than a week or two can be a sign of depression, a type of mental illness. Anxiety was a problem for some of the kids, too. A mind that won’t stop racing can be a sign of depression or anxiety. Poor sleepers also were more likely to have stomach problems and headaches. 

Cheng thinks the observations will apply to teens, as well, since this fits with what has been seen in older kids. 

The night shift

Missing sleep is especially dangerous for children and teens. That’s because their brains won’t finish developing until about age 25. The size of the brain doesn’t change much from childhood to adulthood, Cheng explains. But how the brain is organized — how its nerves connect to one another — changes a lot. “This happens as we learn new things and interact with society,” he says. And this rewiring takes place mostly during sleep. In fact, this reorganizing of the brain’s circuitry, “is essential for young people whose brains are still developing,” he says. 

Kyla Wahlstrom is a professor at the University of Minnesota in Minneapolis. She’s an expert on teens and sleep. It can feel like your brain just shuts down when you go to sleep. In fact, she notes, the brain is even more active when you’re asleep than when you’re awake. 

In addition to reorganizing itself, the night brain also stays busy organizing memories. Wahlstrom explains it like this: At night, your brain sorts information to link related facts. That makes it easier to locate memories when you need them. Think of it like putting information into file folders on your computer. The brain also tags these memories by the emotions associated with them. Then the brain cleans up and tosses out any extra information that isn’t important enough to keep. 

But there’s a catch. It takes the brain longer to organize negative emotions than positive ones. If you don’t get enough sleep, your brain might not have time to finish tidying up. If the brain runs out of time, you’re left with negative emotions still cluttering your brain. That may explain why Cheng found that not getting enough sleep was associated with mood problems, says Wahlstrom. 

Cheng’s team didn’t look at cause and effect. They just observed that mood problems and lack of sleep tend to go together. Figuring out whether one might cause the other will be the subject of another study, Cheng says.

For now, Wahlstrom says, the message is clear: Get plenty of sleep!