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Not enough sleep can harm school-age kids' brain development, study finds

Regularly sleeping less than nine hours a night can affect a child's brain, behavior, cognition and mental health, a new study found.
/ Source: TODAY

Not getting enough sleep can put a damper on your day. But for elementary-school age kids, routinely sleeping less than nine hours at night may have a lasting effect on neurocognitive development, according to a new study published in The Lancet Child & Adolescent Health by researchers at the University of Maryland School of Medicine. 

“Sleep is very important for kids’ brains,” said Ze Wang, Ph.D., study author and professor of diagnostic radiology and nuclear medicine at University of Maryland School of Medicine, told TODAY.

During early adolescence, children experience rapid growth and development, and sleep plays a big role, said Wang. But there is a growing trend of children and adolescents sleeping less, he added.

So researchers decided to measure the effects of insufficient sleep during this age on the development of the brain, cognition and behavior. The study included data from 8,323 children ages 9 to 10 enrolled in the ongoing Adolescent Brain Cognitive Development (ABCD) study, the largest long-term study of brain development and child health in the U.S.

The children were split into two groups based on their sleep patterns: those who got sufficient sleep and those who got insufficient sleep, defined as sleeping less than 9 hours a night. 

Researchers assessed behavioral problems, mental health, cognition, brain structure and brain function at baseline (or the start of the study) and again two years later, the researchers wrote.

What did the study find?

“In the cohort with insufficient sleep, in the brain we observed those kids showed a smaller gray matter volume in some key brain regions related to many different high-order functions like memory, attention and inhibition control,” said Wang. Less gray matter is a sign that insufficient sleep has negative effects on brain structure, Wang explained, which are consistent with the behavioral and mental health findings of the new study.

Outside the brain, the researchers observed negative effects of insufficient sleep on memory, anxiety, depression, problem-solving, and school performance.

While the researchers expected to see some negative effects of insufficient sleep on the brain, Wang said they were surprised by how long they lasted. “What we found kind of striking … is that all of the children were healthy, and the negative effects of sleep insufficiency were modest, but that modest effect lasted for two years,” said Wang.

“We’re saying two years because we only have data from two years, but the effects could last longer,” he added. If children don't change their sleep habits, it's possible that these effects could become permanent, said Wang, adding that further research is needed.

The researchers concluded that the study results provide evidence of the “long-lasting effect of insufficient sleep” on neurocognitive development in early adolescence. 

Up until now, most research on sleep and brain development has focused on early childhood, Dr. Caroline Martinez, developmental-behavioral pediatrician and assistant clinical professor of pediatrics at Mount Sinai, told TODAY. “This study covers what we consider to be the forgotten years, that middle childhood range,” she said, adding that this is a key time because an “incredible” amount of brain maturation occurs during preadolescence.

“There’s a big increase in the connections between nerve cells and also a refining of the connections. Sleep is very important for that process of strengthening the connections,” Martinez said.

Sleep is also critical to physical health during this time because too little sleep can suppress the release of growth hormone, according to Nemours Children's Health.

Why are preteens sleeping less?

It’s normal for kids to fall asleep later as they enter adolescence, Martinez noted. “Teens have this circadian clock shift, where they have a delayed release of (the sleep hormone) melatonin, so it’s notoriously harder to fall asleep at the same time as they used to before puberty,” she said. 

The recent trend of preteens getting less sleep likely has more to do with external factors like increased screen use, the experts noted.

“In modern society, there is more stimulation, such as mobile phones, games and social media. … Today kids are not only busy in real life but also busy in virtual life,” Wang said.

The bright light from screens can also suppress melatonin levels, said Martinez. “People don’t realize that (children's) pupils are even larger than ... adults, so there’s more of an effect of that light from the screens, suppressing melatonin production,” she added.

In the study, the researchers wrote that the findings also highlight the “value of early sleep intervention” to improve long-term outcomes.

How to help kids fall and stay asleep

“Parents should be pretty firm and consistent about bedtimes and follow guidelines on the amount of sleep that kids should get, which changes depending on the age,” said Martinez.

The American Academy of Sleep Medicine recommends the following amount of daily sleep for children to promote optimal health:

  • 1–2 years: 11 to 14 hours (including naps) 
  • 3–5 years: 10 to 13 hours (including naps) 
  • 6–12 years: 9 to 12 hours 
  • 13–18 years: 8 to 10 hours

Here are tips to help your child get enough sleep from the experts:

No screens in the bedroom after bedtime.

“Parents should cut the kids’ total daily screen time as much as they can. … One effective rule is no phone, no iPad, or no PC in the bedroom after bedtime,” said Wang.

Eliminating screens from the bedroom not only removes the temptation for kids, Martinez said, but it also helps minimize noise and light, which is conducive to a good night’s sleep. 

Establish a relaxing pre-bedtime routine. 

Routines can help kids wind down and relax.

“I would recommend cutting screens off 60 minutes prior to bedtime and keep a consistent schedule with that cutoff,” said Martinez. Research has shown that your core body temperature needs to cool down in order to fall asleep, and a bath or shower can help with that, she added. Other relaxing pre-bedtime activities include reading or listening to music.

Encourage physical activity during the day.

“We should encourage kids to get more physical activity during the daytime,” said Wang, adding that exercise can not only help improve sleep quality but can also promote mental health.

Limit caffeine. 

“Caffeinated drinks are being more and more marketed to teens and preteens,” Martinez warned. Martinez recommended parents make sure their children do not have any caffeinated beverages at least four hours before bedtime.

Keep it consistent on weekends.

It’s important for kids to try to maintain a consistent sleep schedule over the weekend so they aren’t playing catch-up afterwards. “If kids are staying up later on Friday and Saturday, (on) Sunday, they’ll have a hard time falling asleep, which can perpetuate that insomnia during the week and make it harder to correct,” Martinez said. 

Shift to a school sleep schedule.

As summer ends, many children are preparing to return to school, mostly in-person this year. “I recommend a good seven to 10 days before school starts, parents start shifting the bed time back about 20 minutes per evening for three days in a row to get kids back on schedule,” said Martinez.

Be careful with sleep aids, like melatonin.

“We like to start with the behavioral recommendations first — sleep hygiene, good routines and consistent limits,” said Martinez.

She added that the safest way to use melatonin if needed is at a low dose in order to reset a child's circadian clock, for example to fight jet lag or if the kid has gone to bed too late too many nights in a row.

“We recommend a dose of about a half a milligram, about an hour before bedtime,” she added.

“Melatonin can be used safely, but it’s not recommended for long-term use or at higher doses,” said Martinez. She stressed that there have been increasing reports of melatonin poisonings and that parents should be careful when storing the supplement around kids, especially the candy-like gummy versions.

Talk about sleep habits.

“A lot of times kids with insufficient sleep don’t act tired or say that they’re tired. They may just become more moody and emotional, or even more hyperactive,” Martinez pointed out. If parents are concerned about how much a child is sleeping, Martinez recommended bringing it up to a pediatrician who can refer the child for a sleep study if necessary.