Napping in children supports learning, memory retention, and consolidation throughout early childhood. 6 Children aged 7 to 12 learned new vocabulary, which was followed by either overnight sleep or daytime wakefulness. Recognition of words improved after sleep. However, the recall of the wake group also showed improvement after a delayed overnight sleep. Similarly, the memory of 9 to 12-year-olds in a word-matching exercise was enhanced after overnight sleep. 6 Therefore, overnight sleep appears to facilitate the consolidation of declarative memory in children, even when there are delays between the initial learning and the sleep period. 6 Sleeping soon after acquiring knowledge may also be advantageous in later stages of life. High school students studying vocabulary from a foreign language showed increased forgetting when they learned at least 12 hours before sleep, compared to learning just a few hours before sleeping. Studies have shown that memory retention was comparable among teenagers who slept for 4 to 5 hours as against those who slept for 9 hours. 6
A lack of sleep has been associated with impaired cognition, 1, 11, 12, 29 cognitive slowing, 15 impaired memory, 11, 15 impaired memory consolidation, 1 impaired executive control tasks, 11 decrease in vigilance, 15 impaired performance on attention, 11 decreased sustained attention, 15 impaired neurobehavioural performance, 2 diminished motivation, 12 decreased brain glucose utilisation, 1 and impairment of the glymphatic system. 1 Sleep disruption is particularly widespread in people with neurodegenerative dementias. 30 Betaamyloid has been correlated with reduced REM sleep amount in healthy older adults and patients with Alzheimer’ s Disease. 30
Sleep deficiency, weight gain, and obesity Lack of sleep has been linked to an increased risk of obesity, 2, 8, 9, 31, 32 increase in body mass, 8 8, 26, 31
and weight gain. Lack of sleep down-regulates the satiety hormone leptin, 1, 26 and up-regulates the appetite-stimulating hormone ghrelin, 1, 26 while also contributing to adipokine dysfunction, 1 and increased hunger, 1, 8, 26 appetite, 8 and food intake, 13 contributing to nocturnal free fatty acids, 1 which can lead to dysregulation of the neuroendocrine control of appetite. 10 To expand on this, disrupted sleep leads to a disturbance in the normal equilibrium of ghrelin and leptin, two hormones that regulate hunger and feelings of fullness, respectively. When these hormones are not in balance, individuals often experience heightened hunger and appetite, along with a diminished sense of fullness, thereby raising the risk of obesity and type 2 diabetes. 1