While we sleep, the brain remains biologically active. Sleep supports learning and memory, emotional regulation, metabolic function and many of the processes involved in maintaining physical and mental health.
Poor sleep can affect how we feel, think and function the following day. When sleep problems become persistent, they can also interact with mental-health conditions in important ways.
The relationship works in both directions: mental health can disrupt sleep, and disrupted sleep can make mental-health symptoms harder to manage.
That is why SLEEP is one of the six areas of the ASCEND framework. ASCEND translates evidence into six practical areas for building brain health, resilience and wellbeing.
The aim is not perfect sleep. It is to understand what supports healthy sleep, recognise when a sleep problem needs proper treatment, and make practical changes that are supported by evidence.
Sleep is active biological maintenance
Sleep is sometimes treated as the part of the day when nothing happens. Biologically, that is far from true.
Across the night, the brain moves through different stages of non-REM and REM sleep. These stages are associated with changes in brain activity, autonomic function, hormone signalling and memory processing.
Sleep contributes to:
- learning and memory
- attention and cognitive performance
- emotional processing
- immune and metabolic regulation
- physical recovery
After a poor night of sleep, concentration may be worse. Irritability can increase. Emotional reactions may feel more intense. Motivation and decision-making can become harder.
One bad night is usually something the body can tolerate. The greater concern is when inadequate, irregular or disrupted sleep becomes a pattern.
Sleep and mental health influence each other
There is no single sleep pattern that explains mental illness. But the relationship between sleep and mental health is substantial.
Sleep disturbance is common across conditions including depression, anxiety disorders, bipolar disorder, ADHD and substance-use disorders.
Importantly, sleep problems should not always be viewed simply as a symptom of another psychiatric condition. Insomnia can persist even after other symptoms improve. It can contribute to ongoing distress and impairment, and treating insomnia directly may improve both sleep and some mental-health outcomes.
What is causing the poor sleep—and does the sleep problem itself now need treatment?
How much sleep do we actually need?
There is no biologically meaningful rule that every adult must get exactly eight hours.
The American Academy of Sleep Medicine and Sleep Research Society recommend that adults generally obtain at least seven hours of sleep per night on a regular basis to support optimal health. For many adults, somewhere around seven to nine hours is appropriate, but individual sleep need varies.
The more useful question is not simply, “Did I get eight hours?” It is, “Am I regularly getting enough sleep to function well during the day?”
Persistent daytime sleepiness, impaired concentration, irritability or needing to compensate heavily with caffeine may be clues that sleep quantity or quality deserves attention.
Regularity matters too
Sleep duration receives most of the attention, but when we sleep also matters.
The brain has an internal circadian timing system that helps coordinate sleep and wakefulness across approximately 24 hours. Regular patterns of waking, light exposure, activity and meals provide signals that help keep this system aligned.
Increasing evidence suggests that greater irregularity in sleep timing is associated with poorer mental-health outcomes, including depressive and anxiety symptoms. However, this evidence is largely observational. It does not mean that an irregular weekend automatically causes depression, nor that everyone needs a rigid bedtime.
A more practical goal is reasonable consistency, particularly around wake time.
Light is one of the brain's strongest time signals
The circadian system responds strongly to light. Bright light in the morning helps signal to the brain that the biological day has begun. In contrast, substantial bright light late at night can shift sleep timing later in susceptible people.
This is one reason morning outdoor light can be useful when trying to establish a more stable sleep-wake rhythm. For many people, simply getting outside relatively soon after waking is a practical starting point.
The timing and intensity of light can matter clinically, however, particularly in people with circadian-rhythm disorders or bipolar disorder. Formal bright-light therapy is therefore different from simply encouraging normal morning daylight exposure.
Insomnia is more than “bad sleep hygiene”
Sleep hygiene refers to behaviours and environmental factors that can support healthy sleep: limiting late caffeine, creating an appropriate sleep environment, reducing disruptive late-night stimulation and maintaining reasonably regular routines.
These are sensible foundations. But established chronic insomnia is not simply the result of failing to follow enough sleep tips.
Major clinical guidelines recommend Cognitive Behavioural Therapy for Insomnia (CBT-I) as the first-line treatment for chronic insomnia in adults.
CBT-I typically combines several components, which may include:
- stimulus control
- sleep restriction or sleep compression
- cognitive strategies
- relaxation approaches
- education about sleep
- behavioural changes that strengthen the association between bed and sleep
Sleep hygiene alone is not considered an adequate treatment for chronic insomnia. Someone can avoid screens, drink herbal tea, buy blackout curtains and still have clinically significant insomnia.
That person does not necessarily need more sleep tips. They may need proper assessment and evidence-based treatment.
Treating insomnia may also help mood
Research increasingly suggests that treating insomnia with CBT-I can improve more than sleep.
A 2024 meta-analysis examining CBT-I in people with major depressive disorder found improvements in both insomnia and depressive outcomes compared with control conditions.
This does not mean CBT-I replaces appropriate treatment for depression. It means that when depression and insomnia occur together, treating the insomnia may be an important part of comprehensive care rather than waiting for it to disappear once the depression improves.
Sleep can provide important clinical information
Depression and anxiety
Difficulty falling asleep, repeated waking, early-morning waking and non-restorative sleep are common in depression and anxiety. Some people with depression experience the opposite pattern and sleep excessively.
Sleep disturbance can worsen concentration, energy and emotional regulation, potentially amplifying symptoms already caused by the underlying condition.
Bipolar disorder
A reduced need for sleep, especially when accompanied by increased energy, elevated or irritable mood, increased activity, impulsivity or unusually rapid thinking, may be an early sign of hypomania or mania.
This is different from insomnia. Someone with insomnia usually wants to sleep but cannot. Someone developing mania may sleep very little and not feel that they need more sleep. That distinction matters clinically.
ADHD
Sleep disorders and sleep difficulties are common in adults with ADHD. Problems may include insomnia, delayed sleep timing, restless legs symptoms and other sleep disorders.
Poor sleep can also worsen attention, working memory and emotional regulation—symptoms that can overlap with ADHD itself. Persistent sleep problems therefore deserve assessment rather than automatically being attributed to ADHD.
Caffeine: useful, but not neutral
Caffeine improves alertness, which is precisely why it can interfere with sleep.
A systematic review and meta-analysis found that caffeine consumption reduced total sleep time, reduced sleep efficiency and increased the time required to fall asleep. The effect depends on the dose, the person and the timing.
There is therefore no universal rule that everyone must stop caffeine at exactly the same hour. But if sleep is difficult, moving caffeine earlier in the day is one of the simplest variables worth testing.
Remember that caffeine is not limited to coffee. Tea, energy drinks, pre-workout products, cola and some medications may also contain meaningful amounts.
Alcohol can make you sleepy without improving sleep
Alcohol may shorten the time it takes to fall asleep, which can create the impression that it helps. But sedation is not the same as healthy sleep.
As alcohol is metabolised, sleep can become more fragmented later in the night. Alcohol can also worsen snoring and sleep-disordered breathing in susceptible people.
“It helps me fall asleep” may be true. “It improves my sleep” is a different question.
When sleep needs more than lifestyle changes
Not every sleep problem should be managed by changing habits. Clinical assessment is particularly important when there is:
- persistent insomnia causing distress or daytime impairment
- significant daytime sleepiness
- loud snoring, choking or witnessed pauses in breathing
- unusual movements or behaviours during sleep
- uncomfortable urges to move the legs at night
- a major shift in sleep timing that interferes with normal functioning
- dependence on alcohol or medication to initiate sleep
- rapidly decreasing sleep accompanied by increased energy or other possible symptoms of mania
- sleep disturbance occurring alongside significant deterioration in mental health
Sometimes the problem is insomnia. Sometimes it is sleep apnoea, restless legs syndrome, a circadian-rhythm disorder, medication effects, substance use, another medical condition or a psychiatric disorder. The treatment depends on the cause.
A practical place to start
- Protect enough time for sleep. You cannot consistently obtain seven or eight hours of sleep if your schedule only allows five or six.
- Anchor your wake time. Try to wake within a reasonably consistent window most days rather than chasing a perfect bedtime.
- Get light early in the day. Normal outdoor morning light provides a strong timing signal to the circadian system.
- Move caffeine earlier if sleep is difficult. Experiment with the timing rather than assuming caffeine has no effect because you can fall asleep after drinking it.
- Create a transition into sleep. Allow some separation between a highly stimulated day and getting into bed.
- Do not turn the bed into a place for prolonged wakefulness. This is one of the principles addressed more systematically in CBT-I.
- If insomnia persists, treat insomnia. Do not spend months accumulating more sleep-hygiene tricks when an evidence-based treatment exists.
The ASCEND principle
Sleep is not a performance competition. Wearable devices, sleep scores and optimisation strategies can be useful, but they can also make people increasingly anxious about whether they are sleeping “correctly.”
The objective is not perfect sleep. It is sufficient, reasonably regular and restorative sleep that supports daytime functioning and health.
And when sleep is persistently poor, the answer may not be trying harder. It may be understanding why.
Don't aim for perfection. Aim upward.
Protect sleep. Respect the biology. Treat the problem when it becomes a disorder.
CBT-I recommendations are supported by guidelines and randomised treatment evidence. Sleep-regularity findings include substantial observational research, so association should not automatically be interpreted as causation.
Clinical note
ASCEND is an educational framework and does not replace individual medical or psychiatric assessment.
Sleep problems can sometimes be symptoms of medical, neurological, respiratory or psychiatric conditions. Persistent or concerning changes in sleep should be discussed with an appropriately qualified healthcare professional.