Results from a review and meta-analysis of almost 13 million total participants from nine countries showed that, across multiple different psychotic disorders, there was a 2.5-fold higher risk of developing dementia later in life compared with individuals who did not have a disorder. This was regardless of the age at which the patients first developed the mental illness.
Moreover, participants with a psychotic disorder tended to be younger than average when diagnosed with dementia. Two studies showed that those with psychotic disorders were more likely to be diagnosed with dementia as early as in their 60s.
“The findings add to a growing body of evidence linking psychiatric disorders with later cognitive decline and dementia,” senior investigator Jean Stafford, PhD, a research fellow at MRC Unit for Lifelong Health and Ageing, University College London, told this news organization.
Dr. Stafford noted that the results highlight the importance of being aware of and watchful for symptoms of cognitive decline in patients with psychotic disorders in mid- and late life.
“In addition, given that people with psychotic disorders are at higher risk of experiencing multiple health conditions, including dementia, managing overall physical and mental health in this group is crucial,” she said.
The findings were published online in Psychological Medicine.
Bringing the evidence together
There is increasing evidence that multiple psychiatric symptoms and diagnoses are associated with cognitive decline and dementia, with particularly strong evidence for late-life depression, Dr. Stafford said.
“However, the relationship between psychotic disorders and dementia is less well-established,” she added.
Last year, her team published a study showing a strong association between very late onset psychotic disorders, defined as first diagnosed after age 60 years, and increased risk for dementia in Swedish population register data.
“We also became aware of several other large studies on the topic published in the last few years and realized that an up-to-date systematic review and meta-analysis was needed to bring together the evidence, specifically focusing on longitudinal studies,” Dr. Stafford said.
The researchers searched four databases of prospective and retrospective longitudinal studies published through March 2022. Studies were required to focus on adults aged 18 years or older with a clinical diagnosis of a nonaffective psychotic disorder and a comparison group consisting of adults without a nonaffective psychotic disorder.
Of 9,496 papers, the investigators selected 11 published from 2003 to 2022 that met criteria for inclusion in their meta-analysis (12,997,101 participants), with follow-up periods ranging from 1.57 to 33 years.
The studies hailed from Denmark, Finland, Sweden, the United Kingdom, the United States, Australia, Taiwan, New Zealand, and Israel.
Random-effects meta-analyses were used to pool estimates across studies. The researchers assessed the risk of bias for each study. They also included two additional studies in the review, but not the meta-analysis, that focused specifically on late-onset acute and transient psychosis and late-onset delusional disorder.
The other studies focused on late-onset schizophrenia and/or very late onset schizophrenia-like psychoses, schizophrenia, psychotic disorders, and schizophrenia in older people.
Most studies investigated the incidence of all-cause dementia, although one study focused on the incidence of Alzheimer’s disease.