Insomnia was linked to a 26 per cent higher stroke risk and 28 per cent higher odds of hospital admission, according to a large evidence review.
The review also found associations with depression and suicidal behaviours, while evidence suggested a link with dementia, particularly Alzheimer’s disease.
A previous analysis estimated that insomnia meeting international diagnostic criteria affects around 22 per cent of the general population.
Lead author Luca Vignatelli, of IRCCS Istituto delle Scienze Neurologiche di Bologna in Italy, said: “Insomnia deserves attention as a warning sign of the status of brain and mental health.
“These findings show that someone with insomnia has an increased risk for dementia or stroke.
“Insomnia should be recognised and addressed as part of a wider approach to health to reduce the risk of developing such disorders.”
The review, funded by the European Academy of Neurology (EAN), examined evidence across seven health outcomes. Researchers searched MEDLINE and EMBASE up to August 2025 and combined existing systematic reviews with three new reviews of primary studies.
For stroke, nine eligible studies were identified, with six included in the meta-analysis. The systematic review included more than 1.3 million participants overall.
The association between insomnia and stroke varied substantially between studies.
Five studies examined hospitalisation, with three included in the meta-analysis. The analysis found 28 per cent higher odds of hospital admission for any reason among people with insomnia.
Evidence on dementia was less consistent. Most reviews found an association between insomnia and dementia from any cause, but findings differed between studies.
Evidence was more consistent for Alzheimer’s disease, while findings for vascular dementia were mixed.
The researchers stressed that the review identified associations and did not establish that insomnia directly causes stroke, dementia or the other conditions studied.
They also noted differences in how insomnia was defined across studies and limited consideration of sleep medication use.
The work examined seven outcome areas: dementia, stroke, depression, suicidal behaviour, mortality, occupational injuries and hospitalisation.
The researchers said future studies should use shared diagnostic criteria, include populations from under-researched regions and better distinguish the effects of insomnia from those of medicines used to treat it.
Study author professor Stefan Seidel said: “Sleep should be part of the conversation about brain health at every age.
“We need to raise awareness of insomnia and its treatment, and make sure sleep is included in health promotion programmes in our communities, schools and workplaces.”
