Adolescents who sleep for longer tend to have improved brain function, Cambridge study suggests

Adolescents who sleep for longer and have an earlier bedtime tend to have improved brain function and perform better at cognitive tests, researchers have found.

But the study showed even those with better sleeping habits were not getting the amount of sleep recommended for their age group.

It is believed that while we are asleep, toxins that have built up in our brains are cleared out, and brain connections are consolidated and pruned, which enhances memory, learning and problem-solving skills. Sleep also boosts our immune systems and improves our mental health.

During adolescence, we tend to start going to bed later and sleeping less, which impacts our body clocks at time of important development in our brain function and cognitive development.

The American Academy of Sleep Medicine advises eight and 10 hours of sleep each night during this time.

Prof Barbara Sahakian, from the Department of Psychiatry at the University of Cambridge said: “Regularly getting a good night’s sleep is important in helping us function properly, but while we know a lot about sleep in adulthood and later life, we know surprisingly little about sleep in adolescence, even though this is a crucial time in our development. How long do young people sleep for, for example, and what impact does this have on their brain function and cognitive performance?”

Using data from the Adolescent Brain Cognitive Development (ABCD) Study, the largest long-term study of brain development and child health in the United States, the team looked at data on sleep patterns from more than 3,200 children aged 11 to 12 who were given FitBits to record their sleep patterns. They checked the results against two further groups of children aged 13 to 14, with 1,190 participants.

The children fell broadly into of three groups:

Group One (39 per cent of them) slept an average of 7 hours 10 minutes. They tended to go to bed and fall asleep the latest and wake up the earliest.

Group Two (24 per cent) slept an average of 7 hours 21 mins. They had average levels across all sleep characteristics.

Group Three (37 per cent) slept an average of 7 hours 25 mins. They tended to go to bed and fall asleep the earliest and had lower heart rates during sleep.

Although there were no significant differences in school achievement between the groups, group three performed better at cognitive tests looking at aspects such as vocabulary, reading, problem solving and focus, followed by group two, with group one performing worst.

Group three also had the largest brain volume and best brain functions, with Group One the smallest volume and poorest brain functions.

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

First author Dr Qing Ma, from Fudan University, said: “Although our study can’t answer conclusively whether young people have better brain function and perform better at tests because they sleep better, there are a number of studies that would support this idea. For example, research has shown the benefits of sleep on memory, especially on memory consolidation, which is important for learning.”

Group Three had the lowest heart rates across the sleep states and Group One the highest. Lower heart rates are usually a sign of better health, whereas higher rates can accompany poor sleep quality like restless sleep, frequent awakenings and excessive daytime sleepiness.

Senior author Dr Wei Cheng from Fudan University added: “Given the importance of sleep, we now need to look at why some children go to bed later and sleep less than others. Is it because of playing videogames or smartphones, for example, or is it just that their body clocks do not tell them it’s time to sleep until later?”

The ABCD Study is a longitudinal one, following participants over time, so the team was able to show the differences in sleep patterns, brain structure and function, and cognitive performance, tended to be present two years before and two years after the snapshot they studied.

The research, published in Cell Reports, was supported by the National Key R&D Program of China, National Natural Science Foundation of China, National Postdoctoral Foundation of China and Shanghai Postdoctoral Excellence Program. The ABCD Study is supported by the National Institutes of Health.