Severe psychiatric disorders are associated with increased risk of dementia

Abstract

Background: Individuals with psychiatric disorders have an increased risk of developing dementia. Most cross-sectional studies suffer from selection bias, underdiagnosis and poor population representation, while there is only limited evidence from longitudinal studies on the role of anxiety, bipolar and psychotic disorders. Electronic health records (EHRs) permit large cohorts to be followed across the lifespan and include a wide range of diagnostic information.

Objective: To assess the association between four groups of psychiatric disorders (schizophrenia, bipolar disorder/mania, depression and anxiety) with dementia in two large population-based samples with EHR.

Methods: Using EHR on nearly 1 million adult individuals in Wales, and from 228 937 UK Biobank participants, we studied the relationships between schizophrenia, mania/bipolar disorder, depression, anxiety and subsequent risk of dementia.

Findings: In Secure Anonymised Information Linkage, there was a steep increase in the incidence of a first diagnosis of psychiatric disorder in the years prior to the diagnosis of dementia, reaching a peak in the year prior to dementia diagnosis for all psychiatric diagnoses. Psychiatric disorders, except anxiety, were highly significantly associated with a subsequent diagnosis of dementia: HRs=2.87, 2.80, 1.63 for schizophrenia, mania/bipolar disorder and depression, respectively. A similar pattern was found in the UK Biobank (HRs=4.46, 3.65, 2.39, respectively) and anxiety was also associated with dementia (HR=1.34). Increased risk of dementia was observed for all ages at onset of psychiatric diagnoses when these were divided into 10-year bins.

Conclusions: Psychiatric disorders are associated with an increased risk of subsequent dementia, with a greater risk of more severe disorders.

Clinical implications: A late onset of psychiatric disorders should alert clinicians of possible incipient dementia.

Keywords: Adult psychiatry; Data Interpretation, Statistical; Depression & mood disorders; Schizophrenia & psychotic disorders.

Figure 1

Distribution of differences between the age of first diagnosis of a psychiatric disorder and age of diagnosis for dementia in (A) Secure Anonymised Information Linkage databank and (B) UK Biobank, assigning people to the diagnostic category corresponding to their highest-ranking diagnosis. AAO, age at onset.

Figure 2

Kaplan-Meier curves for survival models in Secure Anonymised Information Linkage (A) and UK Biobank (B) estimating dementia risk by hierarchical psychiatric diagnosis group membership, controlling for sex and deprivation. Ribbons are 95% CIs.

Figure 3

Percentage of people developing dementia corresponding to psychiatric disorder age at onset bins in (A) SAIL databank and (B) UK Biobank. Data are presented for individuals excluding those who developed psychiatric conditions in the same year or after dementia diagnosis. SAIL, Secure Anonymised Information Linkage.