related to cardiometabolic health, mental health, cognitive health, weight gain, obesity, reproductive health, hormonal health, muscle health, and immune health.
Sleep deficiency and cardiometabolic health Suboptimal sleep impairs cardiometabolic health. 1, 4 The quality of sleep has a significant effect on the cardiovascular system. During healthy sleep, the heart rate slows down, blood pressure decreases, and there is a shift in autonomic balance from sympathetic dominance to a more parasympathetic state. This resting period of the cardiovascular system appears essential for maintaining optimal cardiovascular health. Elevated autonomic activity places additional stress on the cardiovascular system, thereby increasing the risk of adverse cardiovascular events. 1 A lack of sleep has been associated with cardiovascular disease, 12 coronary heart disease, 2, myocardial infarction, 1 stroke, 1 metabolic syndrome, 2, 24, 25 2, 12, 13
type 2 diabetes, decreased insulin sensitivity, 13 insulin resistance, 1 β-cell dysfunction, 1 altered glucose homeostasis, 26 impaired glucose tolerance, 13 endothelial dysfunction, 1 hypertension, 1, 2 increased risk for arrhythmia, 1 and increased autonomic arousal. 1
It is interesting to note that epidemiological studies show that the link between sleep duration and cardiovascular events, as well as overall mortality, follows a J-shaped pattern. Both too little sleep, under 6 hours, and too much sleep, over 9 hours, are associated with a higher risk of cardiovascular death and death from all causes. 1 A systematic review and metaanalysis found a“ U-shape” relationship between sleep duration and metabolic syndrome. 25, 27 A meta-regression of 40 prospective cohort studies involving 2,200,425 participants revealed a J-shaped association between sleep duration and all-cause mortality. Both shortened( less than 7 hours) and prolonged sleep durations( greater than 8 hours) were associated with increased risk of all-cause mortality. 28 The meta-regression analysis concluded that long sleep appeared to be a greater risk factor for mortality than short sleep. 28
Sleep deficiency and mental health Suboptimal sleep affects mental health. 1, 4 The period of sleep during the night in humans is characterised by a significant reduction in the activity of the two primary stress systems: the hypothalamicpituitary-adrenal( HPA) axis and the sympathetic nervous system. This reduction is accompanied by a decrease in the blood concentrations of cortisol, adrenaline, and noradrenaline. 5
Sleep plays a significant role in how adults process and manage emotions. 6 In adults, the processing of emotions is often linked to REM sleep; however, recent research indicates that slow-wave sleep also plays a key role. During REM sleep, theta oscillations originating from the amygdala synchronise with the activity of the hippocampus and cortex, which is associated with the enhancement of emotional memories. Furthermore, when emotional memories incorporate declarative components, it is likely that slow-wave sleep also contributes to these components. Likewise, sufficient sleep is essential during childhood to support and enhance emotional processing. 6
There is a two-way link( bidirectional connection) between sleep and mental wellbeing. 1 For example, individuals suffering from depression may experience insomnia, diminished slow-wave sleep, and higher REM sleep disinhibition. Conversely, insomnia and sleep disturbances can act as separate risk factors for depression. 1 Additionally, insomnia and inadequate sleep patterns can increase the risk of anxiety and overall poor mental health. 1
A lack of sleep has adverse effects on mood, 1 irritability, 1 and sense of wellbeing. 1 Sleep quality has also been associated with depression. 2 Research indicates that children aged 8 to 12 demonstrated a decrease in positive affect during a laboratory task and exhibited diminished emotional regulation when subjected to a sleep restriction by 1 hour over a period of 4 days. Similarly, when adolescents aged 14 to 17 experienced a reduction in sleep to 6.5 hours for five consecutive nights, they reported increased levels of emotional dysregulation, a finding that was supported by parental observations. 6
Sleep deficiency and cognitive health The role of sleep in relation to the brain has been described as a process of detoxifying the brain from free radicals, facilitating the replenishment of glycogen, and promoting the formation of memories and synaptic plasticity. 3 Sleep plays a crucial role in the development of the central nervous system. 8
Sleep is essential for stabilising and integrating memories. 29 Suboptimal sleep adversely affects cognitive health. 1, 6, 8 Sleep has been linked to developments in functional brain connectivity. 6 There are links between sleep microstructure and brain maturation. 6 Slow-wave activity propagation is positively associated with the myelin content in both the whole brain and inter-hemispheric regions, whereas the speed of propagation and the extent of cortical involvement are correlated with the myelin content found in the superior longitudinal fascicle. 6 The processes of acquiring and recalling knowledge take place during periods of wakefulness. 1 Sleep plays an essential role in the consolidation of memory, which involves the stabilisation of memories and the integration of learned information into long-term storage. 1 Furthermore, there appears to be a mechanism that filters out unimportant memories, preventing their consolidation. During stage 3 NREM sleep, neuronal replays of representations from the hippocampus facilitate the gradual transformation and integration of these representations into neocortical networks, a process called systemic consolidation. 1 Additionally, brain oscillations during REM sleep contribute to the stabilisation of these transformed memories by enhancing local synaptic plasticity, a phenomenon known as synaptic consolidation. 1
140 | vol31 | no3 | JATMS