Mortality and risk of dementia in individuals with serious mental illness: a population‐based study

Abstract

AbstractBackgroundIndividuals with mental illness such as schizophrenia experience dementia at greater rates than the general population(1). These disorders are also associated with shorter lifespan(2). Consequently, a person with mental illness may be more likely to experience dementia but less likely to live long enough to reach dementia onset. By using deeply phenotyped data across a large portion of person’s lifespan it is possible to examine the causal structure that may lay behind this seeming contradiction.MethodUsing a longitudinal medical record database of 4.5 million individuals in Wales, UK, we were able to follow individuals over a period of two decades. We identified nearly 1 million living individuals aged at least 45 in 1999, of whom one third had diagnoses of psychosis, mania, depression, or anxiety. We tested whether the development of dementia is associated with premorbid mental illness, using Cox regression survival analyses accounting for hospitalisation, history of medication, sex, social deprivation, and cooccurrence between disorders, as compared to matched controls.ResultControlling for the age of onset of mental illness and the reduced lifespan of individuals with these serious mental health disorders, we found a strong relationship between all mental illness and higher risk of dementia. The dementia onset was earlier in individuals with mental illness. We also found a complex relationship with hospitalisation and number of prescriptions, two metrics often associated with disease severity, when explaining mental illness‐related mortality and dementia.ConclusionAll studied mental illnesses are associated with the elevated risk of developing dementia, if individuals survive to a sufficient age. Of these illnesses, psychosis was the strongest risk factor for dementia development. Disease severity and treatment, defined by hospitalisation and medication, are also highly significant factors, with hospitalisation increasing risk of dementia and mortality.