.Sleep is often considered to be a passive state – a nocturnal shutdown which brings an end to one day and switches off the brain until the next day begins.
But this interpretation really does sleep a disservice. From a scientific standpoint, sleep is one of the most active and vital processes in the human body. It plays a role in everything from consolidating memories to managing hormone balance to nurturing emotional stability.
In particular, it is this intricate relationship between sleep and the neuroendocrine system – the system that controls hormone production that most dramatically influences our mental health. Here’s how.
Cortisol – the stress hormone
Cortisol is typically known as the stress hormone. Released by the adrenal gland, it sits alongside hormones such as adrenaline as an integral feature of the human survival instinct – playing a crucial role in the “fight or flight” response.
In addition, cortisol also has a much broader role in the body, regulating our metabolism, managing inflammation, controlling blood pressure and supporting immune function.
One of the most important things to note about cortisol, is that levels in the body are inextricably linked to the circadian rhythm – rising and falling over the course of 24 hours in line with our sleep–wake cycle. Cortisol peaks early in the morning just after we wake up in order to help the body and brain kick into gear.
Over the course of the day, cortisol levels gradually drop until they reach their lowest ebb in the evening. This manifests itself in that tiredness feeling that indicates to us that it is time for bed.
How sleep regulates cortisol and why it matters
Over the course of a typical night’s sleep, we cycle through a series of non-REM sleep stages. These all take place when cortisol levels in the body are low. Towards the end of the night, REM sleep phases become more dominant – a time when emotional memories are processed in the brain and cortisol levels begin to rise.
However, a poor night’s sleep – whether it’s insomnia, sleep apnoea, alcohol consumption, stress or poor sleep hygiene – can affect cortisol levels. Instead of dropping overnight, a number of factors can impact and inhibit the optimal sleep cycle and result in cortisol levels remaining high. And when cortisol levels remain high, the messages being sent to the brain are disrupted further and so the impact on sleep quality is heightened.
Put simply: poor sleep disrupts hormone balance and can lead to worse sleep.
In addition to fatigue, poor quality sleep can in turn lead to:
- Increased anxiety and emotional behaviour
- Impaired memory and decision making
- Higher risk of depression and burnout
- Increased inflammation and metabolic dysfunction
For those who suffer from poor sleep on the odd occasion, the acute issue of cortisol imbalance will not be too damaging. However, if acute sleep disruption turns into chronically poor sleep the health impact – both mentally and physically – can be substantial. In fact, the hippocampus and prefrontal cortex in the brain can eventually wear down and become less adept at managing memory, emotions and mood. Not surprisingly, this ultimately leaves individuals more vulnerable to mental health disorders.
A melting pot of hormones involved in sleep
In addition to cortisol, it’s worth noting that there are a number of other hormones that both influence and are influenced by sleep. These include:
- Melatonin – the sleep hormone that encourages us to fall asleep in the evening
- Serotonin – the neurotransmitter known as the “happy hormone” that supports mood and emotional stability
- Growth hormone – the hormone responsible for cell repair and recovery through the night
Given the role that sleep plays in managing a range of important hormones, it is clear that good quality rest through the night has an integral part to play in mental health and wellbeing. In fact, sleep therapy is now considered to be a core component of treatment for anxiety, PTSD, depression and even bipolar disorder. Clinicians even prescribe sleep as they would with any medication to support mental wellbeing.
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