Media release

From: BMJ Group

Odds of dementia strongly linked to number of co-existing mental health disorders

Increasing from twice as high for one disorder to 11 times as high for four or more
In particular, concurrent mood + anxiety disorder linked to odds of up to 90% for dementia

The odds of developing dementia are strongly linked to the number of co-existing mental health disorders, rising from twice as high for one disorder to 11 times as high for four or more, finds research published in the open access journal BMJ Mental Health.

In particular, the combination of concurrent mood and anxiety disorders is linked to odds of  dementia of up to 90%, the findings indicate.

Psychiatric disorders, such as depression, anxiety, and bipolar disorder, have been individually associated with an increased risk of dementia. But the existing body of research hasn’t assessed the impact of multiple co-existing psychiatric disorders, say the researchers.

In a bid to plug this knowledge gap, they drew on information extracted from the clinical database of the psychiatry department of Bicêtre Hospital, Paris.

They included 3688 patients aged at least 45 and diagnosed with one or more of the most common psychiatric disorders—depression, anxiety, psychosis, substance misuse, personality disorder and bipolar disorder—between August 2009 and October 2023. And they included every type of dementia and cognitive impairment.

The average age of the entire group  was 67: 70 in those with dementia, and 66 in those without. And the average delay between diagnosis of the first psychiatric disorder and dementia diagnosis was 18 months, but ranged from 7 to 13 years.

Nearly 71% (2608) of the patients had one psychiatric disorder; 21.5% (789) had two; 6% (226) had three; and 2% (65) had four or more.

After adjusting for age, sex, and cardiovascular risk factors, the odds of dementia rose in tandem with the number of psychiatric disorders.

Compared with those with one psychiatric disorder, those with two, were twice as likely to be diagnosed with dementia, while those with three, were more than 4 times as likely to do so.

And those with four or more, were 11 times as likely to have dementia.

In particular, the combination of concurrent mood and anxiety disorders was linked to odds of dementia of up to 90%.

The effect of concurrent psychiatric disorders seems to be specific to dementia and suggests they may be early warning signs of it, because further in-depth analysis testing the potential effects on the likelihood of other disease—in this case renal failure–failed to show any link, note the researchers.

This is an observational study, and as such, no firm conclusions can be drawn about cause and effect. And the researchers caution that dementia diagnoses may have been delayed, and, without clinical confirmation, misclassification may have occurred.

All the study participants were also drawn from just one psychiatric department, so may not be representative of all patients with mental health disorders, added to which, information on several potentially influential factors, including socioeconomic status, family history, duration of psychiatric disorder, treatment and brain scans, wasn’t available, the researchers add.

Nevertheless, they conclude:“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.

“Recent advancements in dementia diagnoses, such as the development of biomarkers in blood and cerebrospinal fluid, as well as the use of positron emission tomography, encourage earlier and more accurate detection of dementia.

“Integrating these tools into clinical practice for high-risk individuals, especially those with specific psychiatric comorbidities identified in this study, could significantly enhance their care management, given the recent advancements in dementia treatment.”