For decades, sleep disturbances have been viewed as symptoms of mental illness. A patient develops depression and begins sleeping poorly. Anxiety increases and insomnia follows. Stress rises and sleep deteriorates.¹

But what if we have been looking at the relationship in the wrong direction?

An increasing body of research suggests that poor sleep is not merely a consequence of mental health problems. In many cases, it may be contributing to them, perpetuating them, or even increasing the risk that they develop in the first place.² The implication is profound: improving sleep may be one of the most accessible, scalable and effective mental health interventions available.

The Mental Health Factor We Often Overlook

Discussions about mental ill-health commonly focus on symptom reduction through psychological therapy, medication, resilience, mindfulness and stress management. All are important, yet one of the most fundamental biological requirements for emotional wellbeing is often treated as an afterthought.

Sleep is not simply a period of rest. It is an active biological process involved in memory consolidation, emotional regulation, learning, immune function and recovery. During sleep, the brain performs essential maintenance functions that support cognitive and psychological health.³ Disruptions to this process can have consequences far beyond feeling tired the next day.

The challenge is that sleep problems are remarkably common. Sleep loss and sleep disorders are among the most prevalent and frequently overlooked health problems worldwide. Research consistently demonstrates that insufficient sleep, insomnia and other sleep disorders affect hundreds of millions of people globally and contribute substantially to the burden of mental illness, cardiovascular disease, metabolic disease and reduced quality of life.⁴ Despite this, sleep remains under-recognised in healthcare, underwriting and claims management.

Sleep and Mental Health – A Two-Way Relationship

The relationship between sleep and mental health is often described as bidirectional. Depression, anxiety, post-traumatic stress disorder and bipolar disorder can all disrupt sleep. At the same time, sleep disturbances can worsen psychiatric symptoms and reduce an individual’s ability to cope with everyday stress factors.⁵

Research in 2020 reviewed in The Lancet Psychiatry argues that sleep disturbance may be a contributory causal factor in many mental health conditions rather than simply a secondary symptom. The authors conclude that treating insomnia can reduce symptoms across a range of psychiatric disorders and may even help prevent the onset of clinical mental illness in some individuals.⁶

This observation is supported by everyday experience. After several nights of poor sleep, many people notice increased irritability, heightened emotional sensitivity, difficulty concentrating and a tendency to view challenges more negatively. Sleep deprivation weakens our capacity to regulate emotions, making the stresses of daily life seem larger and more difficult to manage.

The Hidden Impact on Mood, Anxiety and Resilience

One of the most consistent findings in sleep research is the strong association between insomnia and depression.

Studies have demonstrated that insomnia is not only common among people with depression but is also an independent risk factor for developing depressive symptoms. Persistent sleep difficulties are associated with increased anxiety, reduced stress tolerance and a higher risk of suicidal ideation.⁷

Sleep disruption amplifies emotional reactivity. Individuals become more vulnerable to frustration, worry and low mood, while their ability to recover from emotional setbacks declines.⁸ From a practical perspective, poor sleep can undermine many of the psychological coping strategies people rely on to maintain wellbeing and can impact the effectiveness of conventional psychological treatment.⁹

In a world characterised by constant connectivity, demanding workloads and relentless information flow, this matters. Mental resilience is not purely psychological. It is also biological.

Light, Circadian Rhythm and Mental Wellbeing

You could be forgiven for thinking sleep science focuses on what happens during nighttime hours. However, research reminds us that what happens during the day can be equally important.

The human body operates according to an internal circadian rhythm that regulates sleep-wake timing, hormone release, alertness, metabolism and body temperature. This system is heavily influenced by light exposure as shown in Figure 1. Morning light helps synchronise the body’s biological clock, while excessive light exposure late at night can disrupt the timing of sleep.¹⁰

Figure 1 – The Interrelationship of Sleep Factors

Emerging evidence suggests that light exposure may also influence mental wellbeing. Greater daytime light exposure has been associated with better mood and fewer depressive symptoms, while higher nighttime light exposure has been linked to increased risk of depression, anxiety and sleep disturbance.¹¹

The lesson is simple: sleep health and mental health cannot be separated from the circadian rhythm.

Why Better Sleep is Such an Attractive Intervention

Many mental health interventions require specialist services, significant cost or long waiting periods. Sleep interventions are different.

Sleep can often be improved using practical, evidence-based strategies. Sleep hygiene is a term used to describe the set of habits and environmental conditions that support consistent, good-quality sleep. It is not one single practice but a cluster of them, usually grouped into a few areas:

• Timing and routine – going to bed and waking up at roughly the same time every day, including weekends, and following a calming pre-sleep routine.
• Light and environment – getting daylight exposure earlier in the day, limiting bright or blue light in the evening, and keeping the bedroom dark, quiet and cool.
• Substances – limiting caffeine, alcohol, and nicotine, especially in the hours before bed.
• Daytime behaviour – including regular physical activity and avoiding long or late naps that eat into nighttime sleep.
• Pre-bed behaviour – avoiding heavy meals, screens, and stimulating activity close to bedtime, and reserving the bed mainly for sleep (not work or scrolling) so the brain associates it with rest.

Figure 2 – The better sleep feedback loop

The good news is that anyone can improve their sleep hygiene with little to no cost and no negative side-effects. For those who require additional support, management of sleep disorders such as obstructive sleep apnoea, and cognitive behavioural therapy for insomnia (CBT‑I) have shown benefits. CBT‑I in particular is recognised as a highly effective treatment for chronic insomnia and has been shown to improve sleep outcomes and broader mental health outcomes.¹²

Improving sleep may create a positive cycle (Figure 2). Better sleep supports emotional regulation, concentration and energy levels. Improved psychological wellbeing can then further enhance sleep quality. The opposite cycle is also true, which is why sleep problems can become so persistent if left unaddressed.

Implications for Insurers

For insurers, sleep represents a risk factor hiding in plain sight. Sleep disorders are associated with mental ill-health conditions, cardiovascular disease, diabetes, workplace accidents and reduced functional capacity. Untreated sleep problems may contribute to longer disability durations, reduced return-to-work outcomes and increased healthcare utilisation, but questions about sleep are still infrequently asked in routine healthcare settings, and sleep disorders remain substantially underdiagnosed.¹³

Mental health is a significant cause of disability claims and an important topic for life insurers. These claims can be complex and require a good understanding of the biopsychosocial factors at play. As our understanding of the relationship between sleep and psychological wellbeing continues to evolve, one message is becoming increasingly clear: sleep deserves to be viewed as more than a lifestyle issue. It is a fundamental pillar of mental health.

A deeper understanding of sleep may therefore benefit underwriting, claims assessment and rehabilitation planning. It may also help identify opportunities for earlier intervention before more serious health consequences emerge.

Perhaps the most overlooked question we can ask is one of the simplest: How are you sleeping?