The Role of Sleep in Mental Health
Whilst we often think about the importance of sleep for physical health, sleep is also vital for mental health. Short-term sleep loss impacts daytime mood, and chronic sleep disturbances have the potential to contribute to the development of psychiatric disturbances of clinical concern – including depression, anxiety and psychotic disorders.
The chemical messenger systems of sleep and mood
In order to understand how sleep and mental health interact, it is first worth understanding a bit about the physiological nature of sleep.
The switch from wake to sleep, and sleep to wake, is orchestrated by a number of chemical messenger systems using the monoamines (including dopamine, histamine, noradrenaline and serotonin) and gamma-aminobutyric acid (GABA). Levels of these neurochemicals naturally rise and fall across the 24-hour period, allowing the switch between states and stages of sleep. These chemical messenger systems are also in part responsible for natural fluctuations in mood and behaviour, and their dysregulation is related to the symptoms and characteristics of psychiatric illness.
It is perhaps then no surprise that sleep, or lack of it, interferes with the daily variation in mood boosting monoamines, with the potential to contribute to the development of psychiatric illness. As well as these overlapping neurobiological pathways connecting sleep and mental health, evidence suggests there are overlapping genetic and environmental pathways linking sleep disturbances with mood disorders, particularly anxiety and depression (Gregory et al., 2016; Gehrman, et al 2011).
Short-term effects of sleep loss on mental health
We can all relate to the feelings of not getting enough sleep. Short-term sleep loss, even after just one night, can make us feel groggy and exhausted, heighten feelings of frustration and irritability, and make us more prone to feel sad or anxious. The reason for this is that two of the proposed functions of sleep are that it strengthens memories and regulates our emotions.
During the waking day, our senses are bombarded with a profound amount of information, and sleep provides our brain the opportunity to strengthen memories for useful information (synaptic neuroplasticity) and get rid of superfluous information that we no longer need (synaptic pruning) (Tononi & Cirelli, 2014). In other words, sleep provides the opportunity for our brains to learn how to adapt to our ever-changing environment.
Without enough sleep, the brain becomes overwhelmed with clutter, and brain circuits that regulate our emotions (such as the amygdala) over-fire. Over-firing of brain circuitry reduces the ability of our brain to provide appropriate responses to events in our daily lives. This explains why we may react disproportionately negatively, perhaps lashing out at others, or interpreting ambiguous information in a negative light, when we haven’t had enough sleep.
Lack of sleep also contributes to feelings of anxiety, and sleep loss itself acts as a physiological stressor, which sets in motion a perpetual cycle of further sleep disruption. Anxiety triggers the release of noradrenaline – the fight or flight hormone – and abnormally high levels of noradrenaline during the pre-sleep period can make getting to sleep tricky.
Noradrenaline may contribute to an increased heart rate, sweaty palms, higher breathing rate – all things useful if we are about to run away from a tiger or impress a board room with a presentation, but this physiological reaction is not conducive to a good night’s sleep. On the other hand, one night of poor sleep may increase our anxiety and make us worried that we may not get enough sleep the following night. Thus, as with mood, the association between sleep and anxiety is bidirectional – anxiety due to some external stressor may make getting to sleep tricky, but poor sleep itself can act as a physiological stressor which further perpetuates difficulty getting to sleep.
Lack of sleep also contributes to symptoms of psychosis in the general population. Studies have shown that insomnia symptoms, such as difficulty getting to sleep, staying asleep or awakening earlier than desired, predict the development of paranoia and hallucinations at 18-month follow-up (Sheaves et al., 2016, Freeman et al., 2012). Additionally, just one night of poor sleep quality and fragmented sleep is associated with increased paranoia and auditory hallucinations the following day (Mulligan et al., 2016).
Thankfully, for most people, stressors are short term, and sleep returns to normal once particular stressors have passed. But for some individuals, sleep disturbances can have longer term implications.
Long term effects of chronic sleep disturbances on mental health (including depression, anxiety and disorders of psychosis)
Sleep disturbances are risk factors for numerous psychiatric disorders, including major depression, bipolar depression, anxiety disorders, and psychosis (including schizophrenia). In fact, almost all psychiatric disorders exhibit some sleep disturbances and untreated sleep disorders appear to predict relapse (Palagini et al., 2022).
Insomnia symptoms, in particular, are common in individuals with anxiety disorders and major depressive disorder. But if we look even closer at the quality of sleep, we see that major depressive disorder and psychosis exhibit particular abnormalities in rapid eye movement sleep, a sleep stage critical for emotional regulation (Palagini et al., 2022). In fact, some researchers have considered the abnormalities in REM sleep to be a hallmark feature of depression (Palagini et al., 2013).
In addition, these psychiatric disorders all feature abnormalities in the circadian rhythm, which relates to the timing of sleep. Early morning awakening is common in individuals with depression; circadian rhythm abnormalities are evident during the different episodes of bipolar disorder; and abnormalities in the regularity of sleep are common in individuals with schizophrenia, with some individuals having very little regular patterning to the timing they go to sleep or wake up (Wulff et al., 2012).
Abnormalities in dopamine signalling are thought to underlie schizophrenia, and it is likely that dopamine dysregulation is the mechanism linking psychosis and sleep disturbances, given the role of dopamine in the normal control of the sleep-wake cycle (Ashton & Jagganath, 2020).
Can treating sleep problems alleviate mental health problems?
The good news is that the first line treatment for insomnia, cognitive behavioural therapy (CBTI), has been shown to be effective in numerous populations, including those with major depression, anxiety disorders and psychotic disorders. Numerous studies show that successful treatment of disturbed sleep often leads to reduction in mood symptoms. This prevents the development of full-blown mental health disorders, and alleviates the burden of living with mental health problems (Hertenstein et al., 2022). Not only does CBTI improve sleep quality, but also regulates the circadian rhythm, and in turn provides a neuroprotective function, improving markers of stress, inflammation and mood disorders (Kyle and Speigelhalder, 2014).
However, whilst CBTI is the first line treatment for insomnia, access to treatment is prohibitive due to a lack of trained providers nationwide and globally. It is more common for patients with insomnia to be prescribed prescription medications such as benzodiazepines (though these are infrequently prescribed due to their potency and safety profile) or benzodiazepine receptor agonists (BDRA) such as zolpidem or eszopiclone.
However, these medications should only be used in the short-term (<4 weeks) and infrequently, due to increased risk of adverse side effects, as well as the development of tolerance and dependency. The effect of these medications on sleep staging, as well as synaptic neuroplasticity (important for emotional regulation), is largely unknown.
New avenues for the pharmacological management of insomnia in the context of psychiatric disorders are in development and focus on stabilising the circadian rhythm abnormalities present in these populations with melatonin. More evidence is required, however, before the use of melatonin will be recommended (Palagini et al., 2021). More novel pharmacological options on the horizon modulate orexin and dopamine, which have the potential to improve both sleep and mental health (Speigelhalder et al., 2022).
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