Insomnia and mental disorders are linked. But exactly how remains to be a mystery

The 2004 movie The Machinist gives us a striking depiction, albeit a fictional one, of the psychological effects of chronic insomnia.

When people don’t have enough sleep, their memory and concentration are impaired within the short term. They are also less in a position to regulate their emotions.

If sleeping difficulties proceed, longer-term psychological effects can include anxiety, depression, mania and psychosis. Indeed, Christian Bale’s character in The Machinist has increasingly vivid visual hallucinations and paranoid delusions as his insomnia deepens.

The relationship between insomnia and mental disorders is complex. It’s not only a case of “which comes first, the insomnia or the mental disorder?” Insomnia and mental disorders are interrelated in ways we don’t yet fully understand.

What is insomnia? Is it a mental disorder?

Insomnia is, by far, essentially the most common disorder of sleep. An estimated 12-15% of Australian adults at anyone time meet criteria for insomnia.

People with insomnia have frequent and ongoing difficulties in falling and staying asleep, and/or going back to sleep after early waking. Insomnia not only affects people’s quality of sleep, but how they function the following day.

Many of the aspects that trigger insomnia and help maintain its negative long-term effects are psychological or behavioural. These include:

• psychosocial stressors (equivalent to money, work or family problems)

• attentional bias and worry about sleep (the more we predict and worry about sleep, the more serious it gets)

• poor sleep habits (equivalent to irregular sleep and wake times).

Insomnia is just not a mental disorder in the identical way that, say, depression and anxiety are mental disorders. Insomnia is a recognised sleep problem that nonetheless has close links to a wide range of mental disorders.

Many people have each insomnia and a mental disorder

Around half of all people diagnosed with insomnia even have an associated mental disorder. The commonest ones related to insomnia are depression, anxiety, bipolar disorder, post-traumatic stress disorder, and substance-related disorders.

We don’t (yet) know why we see such high levels of mental disorders in individuals with insomnia. But there are several leading theories, including:

• a shared genetic risk for insomnia and a mental disorder. In other words, some people’s genes may predispose them to each conditions

• a shared neurobiological response. How the brain responds to sleep loss could also be connected to how systems within the brain control cognition, emotion and reward. Disturbances of those brain functions are implicated in a variety of mental disorders

• inflammation and/or dysfunction of the immune system may underlie each insomnia and mental disorders.

Which comes first?

Further complicating the image is evidence showing insomnia can occur someone develops a mental disorder, or . Researchers call this a “bidirectional” relationship.

We can’t say one causes the opposite. We can only say there may be a transparent link between them.

This link means diagnosis and treatment of 1 can have implications for diagnosis and treatment of the opposite. For instance, for those who don’t adequately treat insomnia, this will worsen symptoms of somebody’s mental disorder, increasing each the severity and risk of relapse.

A form of talking therapy often known as cognitive behavioural therapy for insomnia (CBTi) goals to alter the unhelpful thoughts, feelings, emotions and behaviours that contribute to insomnia. And, in lots of cases, successful treatment of insomnia with CBTi may treat someone’s mental disorder (and vice versa).

CBTi is especially effective at treating insomnia plus depression, substance use or post-traumatic stress disorder. But it’s less effective at treating insomnia plus psychosis or bipolar disorder.

Filling the gaps

There’s much we don’t know concerning the link between insomnia and mental disorders. Last yr a global panel of experts outlined the research needed to plug the knowledge gaps. Recommendations included:

• longer-term studies starting in childhood and adolescence that collect data on sleep and mental health using wearable or smartphone technologies. The aim is to offer more objective measurement of insomnia and mental health in these younger age groups, and to intervene early if needed

• more studies involving people from diverse social and cultural backgrounds. Sleep practices are sometimes culturally-determined. So researching diverse populations would supply a more comprehensive picture of insomnia and mental disorders

• a greater recognition of individuals’s daytime behaviours and environmental exposures, and their contribution to insomnia and poorer mental health. This includeseating fast food, having disrupted sleep routines (for instance, shift work) and using technology excessively.

Results of this research may have profound implications for accurate diagnosis of each insomnia and mental disorders, and their treatment. The aim is to scale back the burden when these conditions occur together, each for individuals and society more broadly.