Children who do not get enough sleep for one night can be cranky, groggy, or meltdown prone the next day.
Over time, though, insufficient sleep may impair neurodevelopment in ways that can be measured on brain scans and tests long term, a new study shows.
Research published in The Lancet Child & Adolescent Health found that 9- and 10-year-olds who do not get at least 9 hours of sleep most nights tend to have less gray matter and smaller areas of the brain responsible for attention, memory, and inhibition control, relative to children who do get enough sleep.
The researchers also found a relationship between insufficient sleep and disrupted connections between the basal ganglia and cortical regions of the brain. These disruptions appeared to be linked to depression, thought problems, and impairments in crystallized intelligence, a type of intelligence that depends on memory.
The overall patterns persisted 2 years later, even as those who got enough sleep at baseline gradually slept less over time, while those who were not getting enough sleep to begin with continued to sleep about the same amount, the researchers reported.
The results bolster the case for delaying school start times, as California recently did, according one researcher who was not involved in the study.
The ABCD Study
To examine how insufficient sleep affects children’s mental health, cognition, brain function, and brain structure over 2 years, Ze Wang, PhD, professor of diagnostic radiology and nuclear medicine at the University of Maryland, Baltimore, and colleagues analyzed data from the ongoing Adolescent Brain Cognitive Development (ABCD) Study. The ABCD Study is tracking the biologic and behavioral development of more than 11,000 children in the United States who were recruited for the study when they were 9 or 10 years old.
For their new analysis, Dr. Wang’s group focused on 6,042 participants: 3,021 children with insufficient sleep who were matched with an equal number of participants who were similar in many respects, including sex, socioeconomic status, and puberty status, except they got at least 9 hours of sleep. They also looked at outcomes 2 years later from 749 of the matched pairs who had results available.
The investigators determined sleep duration based on how parents answered the question: “How many hours of sleep does your child get on most nights in the past 6 months?” Possible answers included at least 9 hours, 8-9 hours, 7-8 hours, 5-7 hours, or less than 5 hours. They also looked at functional and structural MRI scans, test results, and responses to questionnaires.
Negative effects of inadequate sleep were spread over “several different domains including brain structure, function, cognition, behavior, and mental health,” Dr. Wang said.
The strength of the relationship between sleep duration and the various outcomes was “modest” and based on group averages, he said. So, a given child who does not sleep for 9 hours most nights won’t necessarily perform worse than a child who gets enough sleep.
Still, modest effects may accumulate and have lasting consequences, Dr. Wang said.