According to the World Health Organization, over 55 million people have dementia globally. Dementia is mainly associated with impaired cognitive function, but it can also cause psychiatric impairment, with studies showing that patients with dementia have a higher risk of developing disorders such as depression and anxiety. Additionally, this relationship has been shown to be bidirectional, with those with psychiatric disorders having an increased risk of dementia. However, from these studies it is unclear whether having a higher burden of psychiatric disorders has an effect on dementia risk. In research published in July 2025 in BMJ Mental Health, Edouard Baudouin and colleagues measured the odds of dementia in patients with multiple psychiatric disorders. The study found that the odds of dementia increased with the number of psychiatric disorders, with patients with two psychiatric disorders having 2.3 times higher odds of dementia compared to patients with one psychiatric disorder, which increased to 11.1 times higher odds for patients with four or more psychiatric disorders.
The study collected electronic health records of patients in the psychiatric department of Bicêtre Hospital in France, which were derived from the ‘Assistance Publique-Hôpitaux de Paris’ (AP-HP) Clinical Data Warehouse, from 29 August 2009 to 29 August 2023 (the end of the follow-up period). Patients aged 45 years and over who were diagnosed with a psychiatric disorder using International Classification of Diseases, 10th edition codes from 29 August 2009 to 29 July 2023 were included. These psychiatric disorders were grouped into depressive disorders, anxiety disorders, psychotic disorders, personality disorders, substance use disorders, and bipolar disorders. Patients were followed up until their last recorded hospital contract or until the end of the follow-up period. Dementia diagnosis, which was either established before, during, or after psychiatric diagnoses, was obtained from university hospitals within the AP-HP from 29 August 2009 to 29 October 2023. In total, 3,688 participants were included in the study, 653 of whom had dementia. Increased psychiatric disorder burden was associated with increased odds of dementia. After adjustment for age, sex, and number of cardiovascular risk factors, having two, three, or four or more psychiatric conditions was associated with 2.3 times, 4.6 times, and 11.1 times increased odds of dementia, respectively, compared to having one psychiatric condition.
This study by Baudouin and colleagues provides evidence that the number of psychiatric disorders is a key factor in dementia risk. Therefore, assessing psychiatric disorder burden could be a useful predictor for identifying those vulnerable to dementia. However, this study had a small sample size and only recruited participants from a single psychiatric department, and therefore these results will need to be validated by studies with larger sample sizes. Additionally, as patients could have received a dementia diagnosis before the diagnosis of psychiatric conditions, it is difficult to establish cause and effect.
GlobalData epidemiologists forecast that in France, diagnosed prevalent cases of dementia in those aged 60 years and older will increase from 240,000 cases in 2025 to 290,000 cases in 2032 for men and women.