French study finds multiple psychiatric disorders sharply raise dementia risk
Researchers report that dementia odds increased with each additional mood, anxiety or psychiatric diagnosis — up to an 11-fold rise for four or more conditions
A new French study found that people with two or more psychiatric disorders face substantially higher odds of developing dementia than those with a single diagnosis, with the risk rising as the number of co-occurring conditions increases.
Researchers analyzing medical records of roughly 3,700 patients treated in a Paris psychiatric department reported that about 71% had one psychiatric diagnosis, 21.5% had two, 6% had three and 2% had four or more. Compared with patients who had a single psychiatric disorder, those with two were about twice as likely to be diagnosed with dementia, those with three were more than four times as likely, and those with four or more were about 11 times as likely to develop dementia.
The study, published in BMJ Mental Health, examined records of people who had been diagnosed with one or more common psychiatric conditions — including depression, anxiety, psychosis, substance misuse, personality disorder and bipolar disorder — between August 2009 and October 2023. Investigators said patterns that combined mood disorders and anxiety were particularly associated with higher subsequent dementia probability, with that combination linked to an increase in odds approaching 90% in some analyses.
The authors wrote that "the findings of this study highlight the strong association between the co-occurrence of psychiatric disorders and an increased posterior probability of developing dementia, particularly for patterns with anxiety and mood disorders." They noted the result appeared specific to dementia: additional analyses found no similar association between the psychiatric patterns and other diseases such as renal failure.
The researchers acknowledged several limitations. The sample came from a single psychiatric department, which the authors said supports diagnostic consistency but limits generalizability to broader populations. The study was observational, so it cannot establish cause and effect. The investigators also did not account for some potentially relevant factors, such as family history of dementia or the duration of psychiatric disorders.
Dementia incidence is expected to rise substantially in coming decades as populations age, making early identification of high-risk groups a public health priority. Recent projections cited by researchers estimate an increasing burden of dementia among older adults; other studies have linked individual conditions such as depression, anxiety and bipolar disorder to higher dementia risk, and this analysis is among the first to examine how multiple coexisting psychiatric diagnoses interact with that risk.
Dementia affects cognition and daily functioning and is associated with elevated risk for complications such as falls, infections, cardiovascular problems and malnutrition. Advances in diagnostics — including blood and cerebrospinal fluid biomarkers — and in therapeutic approaches have prompted calls for improved screening for early-stage disease, the study authors said. They recommended integrating dementia-detection tools into clinical practice for people identified as high risk because of specific psychiatric comorbidities.
Experts who commented on the findings described the work as important for identifying candidate groups for targeted screening, while underscoring that observational data do not prove psychiatric disorders cause dementia. Public health researchers have previously argued that addressing modifiable risk factors across the lifespan could reduce the future burden of dementia; mental health conditions increasingly are considered among the factors that may influence long-term cognitive outcomes.
The authors concluded that their results "suggest that concurrent psychiatric disorders may be an early warning sign of and exclusive to dementia," and urged development of targeted screening strategies for patients who develop multiple psychiatric disorders. They said earlier detection and closer monitoring could improve management for high-risk patients given recent advancements in dementia diagnosis and treatment.
Until further research — including studies in larger and more diverse populations and investigations that can better address timing and causality — is available, clinicians and patients should interpret the associations cautiously. The study reinforces the importance of monitoring cognitive symptoms in older adults with psychiatric comorbidities and of coordinating mental health and geriatric care to support earlier evaluation when concerns arise.