Teens who sleep longer have improved brain function, study finds

Adolescents who sleep longer perform better at cognitive tasks, a new study says. (Pexels/Andrea Piacquadio)

Researchers from the U.K. and China have found that teenagers who sleep longer and have an earlier bedtime show improved brain function and perform better in thinking and memory tests.

Published last month in the journal Cell Reports, the study of younger American teenagers showed that even so, those with better sleeping habits were not getting the amount of sleep recommended for their age group.

“We know surprisingly little about sleep in adolescence, even though this is a crucial time in our development,” Barbara Sahakian, a psychiatry professor at the University of Cambridge, said in the news release.

“How long do young people sleep for, for example, and what impact does this have on their brain function and cognitive performance?”

Sleep patterns change during adolescence, the research says. Going to bed later and sleeping for a shorter amount of time affects the body clock, coinciding with an important period of development in our brain function and cognitive development.

The American Academy of Sleep Medicine recommends that teenagers get between eight and 10 hours of sleep during this developmental period.

Dr. Wendy Hall, a sleep specialist and nursing professor emeritus at the University of British Columbia, says the changes in sleep that teenagers go through during this period are due to shifting circadian rhythms, which can lead to higher heart rates and shorter periods of sleep.

“By the time kids are adolescents, they have the same length of sleep cycles as adults do,” Hall told CTVNews.ca.

“But the thing is, because of these shifts in their circadian rhythms, they have a tendency to not feel tired as early in the day, and so they have a tendency to push bedtime back.”

Hall also pointed out that stress plays an important role in the sleep functions of teens.

“Anxious adolescents are more likely to have real problems with their sleep, and they’re also more likely to have problems limiting their mobile phone use dependence,” she says.

“When you put together anxiety and mobile phone dependence, then you’re getting greater risk of sleep disorders in terms of short sleep duration, difficulty falling asleep.”

Breaking down the research

The team led by researchers at Cambridge and Fudan University, Shanghai turned to data from the Adolescent Brain Cognitive Development (ABCD) Study, the largest long-term study of brain development and child health in the U.S.

More than 3,200 teenagers between the ages of 11 and 12 were given FitBits (fitness tracking devices) that allowed the researchers to look at their sleep patterns and compare it to brain scans from cognitive tests.

The team found that the teenagers could be broadly divided into three groups:

• Group One – 39 per cent of participants slept an average of seven hours and 10 minutes, falling asleep the latest and waking up the earliest.
• Group Two – 24 per cent slept an average of seven hours and 21 minutes, with sleep characteristics rated as “average.”
• Group Three – 37 per cent slept an average of seven hours and 25 minutes, went to bed the earliest and had lower heart rates during sleep.

The researchers found that Group Three performed better than the other two groups in cognitive tests with aspects like vocabulary, reading, problem solving and focus.

Group Three also had the best brain functions and the largest brain volume, while Group One ranked lowest in both the categories.

“Even though the differences in the amount of sleep that each group got was relatively small, at just over a quarter-of-an-hour between the best and worst sleepers, we could still see differences in brain structure and activity and in how well they did at tasks,” Sahakian said in a Cambridge release.

“This drives home to us just how important it is to have a good night’s sleep at this important time in life.”

The research showed the benefits of sleep on memory consolidation, which is important for learning, according to the study’s authors.

“Given the importance of sleep, we now need to look at why some children go to bed later and sleep less than others,” senior author of the study, Dr. Wei Cheng from Fudan University added.

“Is it because of playing video games or smartphones, for example, or is (it) just that their body clocks do not tell them it’s time to sleep until later?”

How to help your child

UBC’s Hall says that teens who get an appropriate amount of physical activity can counteract the effects of stress and sleep shortage.

“You don’t want vigorous physical activity within one to two hours of bedtime, it raises your core temperature, and it makes it harder for someone to fall asleep,” she says.

“So, while physical exercise is important, the timing of physical exercise is important too for them, both for decreasing their anxiety and for helping them sleep better at night.

Limiting mobile phone usage and reducing other activities during their study time is crucial when it comes to cognitive functions for teenagers, Hall says.

Teenagers with primary caregivers or parents who give clear directions and enforce bedtimes have longer sleep durations and less fatigue during the day. Additionally, sleep hygiene and caffeine dependency should not be taken lightly, for children and adults alike, according to her.

“What that’s going to do is it’s going to make for longer sleep onset — because you’ve got that caffeine on board, and you can’t relax and fall asleep — and shorter sleep time,” Hall says.

Parents should also be clear about limiting mobile phone usage, she adds, as well as reducing other commitments and activities around the time when they’re trying to study for exams.

“If they try and do it all, they’re just going to end up robbing themselves of sleep,” she says.