People with insomnia face a 26 percent higher risk of stroke, according to a large new review of the evidence.

The umbrella review in Sleep Medicine Reviews covered more than 1.3 million participants across nine studies on stroke. Six of the studies were pooled in a meta-analysis.

The hazard ratio was 1.26, with a 95 percent confidence interval of 1.05 to 1.53. The size of the link varied between studies, but the direction held.

The same review found 28 percent higher odds of hospital admission for any reason among people with insomnia.

It also linked insomnia to higher risks of dementia, especially Alzheimer’s disease, depression and suicidal behavior.

The authors stress the findings show associations, not proof that insomnia directly causes these conditions. Definitions of insomnia also varied across studies.

“Insomnia deserves attention as a warning sign of the status of brain and mental health,” said lead author Luca Vignatelli of Bologna, Italy.

Study author Stefan Seidel added: “Sleep should be part of the conversation about brain health at every age.” The review supports more attention to insomnia in clinical care.