The study found that sleep disruption is a driving factor in the occurrence of paranoia, hallucinatory experiences, and other mental health problems in young adults with an average age of 25.

The research in The Lancet Psychiatry was led by the University of Oxford with Lancaster University and others.

Professor Steven Jones from the Spectrum Centre for Mental Health Research at Lancaster University said: “This very large trial indicates how a digital intervention can improve not only sleep but in doing so can alleviate a range of mental health symptoms including depression, anxiety and psychotic symptoms in University students.”

The researchers aimed to improve sleep in these individuals in order to determine the effect on mental health problems such as paranoia (excessive mistrust), anxiety, and depression. 3,755 university students across the UK were randomised into two groups. One group received online cognitive behaviour therapy (CBT) for insomnia; the other group did not but had access to standard treatments.

This is thought to be the largest ever randomised controlled trial of a psychological treatment for mental health and the first study large enough to determine the effects of treating insomnia on psychotic experiences.

Individuals who received the CBT sleep treatment showed large reductions in insomnia, as well as small, sustained reductions in paranoia and hallucinatory experiences. The treatment also led to improvements in depression, anxiety, nightmares, psychological well-being, and daytime work and home functioning.

Those who received CBT were also less likely over the course of the trial to experience a depressive episode or an anxiety disorder. The research suggests that understanding and treating disrupted sleep could provide a key route for improving mental health.

Daniel Freeman, the study lead and Professor of Clinical Psychology at the University of Oxford and Oxford Health NHS Foundation Trust, said: “Sleep problems are very common in people with mental health disorders, but for too long insomnia has been trivialised as merely a symptom, rather than a cause, of psychological difficulties. This study turns that old idea on its head, showing that insomnia may actually be a contributory cause of mental health problems. A good night’s sleep really can make a difference to people’s psychological health. Helping people get better sleep could be an important first step in tackling many psychological and emotional problems.”

Dr Andrew Welchman, Head of Neuroscience and Mental Health at Wellcome, said: “This is an important study that provides further evidence that sleep is an important factor in understanding mental health problems. This study suggests that improving sleep could provide a promising route into early treatment to improve mental health in young people.”