Living with more than one mental health condition may sharply increase the likelihood of developing dementia, new research has suggested.
While depression, anxiety, and bipolar disorder have long been individually associated with cognitive decline, a French study published in BMJ Mental Health has revealed that patients with multiple psychiatric diagnoses face an even higher risk.
Researchers at Paul Brousse Hospital in Paris examined the medical records of 3,688 psychiatric patients, with an average age of 45, over a period of at least five years. Participants had been diagnosed with one or more common mental health conditions—including depression, anxiety, psychosis, substance misuse, personality disorder, or bipolar disorder—between 2009 and 2023.
The study found a clear pattern:
Patients with two conditions were twice as likely to develop dementia as those with one.
Those with three conditions faced a four-fold risk.
People with four or more conditions were at 11 times greater risk.
In particular, the combination of a mood disorder, such as depression or bipolar disorder, alongside anxiety, was linked to nearly a 90% higher likelihood of dementia.
The researchers noted that while the findings demonstrate a strong association, the study was observational and cannot prove causation. They also cautioned that the results may not apply to the wider population, as all participants were treated within the same psychiatric department.
Nonetheless, they argued that the results highlight the potential of using psychiatric comorbidities as an early warning sign. “Targeted screening strategies should be developed for patients with more than one psychiatric disorder,” the authors wrote, adding that advancements in biomarker testing could improve early detection and treatment.
Dementia currently affects around 900,000 people in the UK, a figure expected to rise to 1.7 million within 20 years as the population ages. Alzheimer’s disease, the most common form, affects nearly a million people and is the nation’s leading cause of death.
Meanwhile, mental illness itself is on the rise. Almost 4 million Britons are now seeking help for mental health conditions, a 40% increase since before the pandemic. Among children, nearly a quarter are thought to have a probable mental disorder, according to the latest Office for National Statistics figures.
The findings come amid growing recognition of lifestyle and health factors that can influence dementia risk. A landmark study last year suggested nearly half of Alzheimer’s cases worldwide could be prevented by addressing 14 risk factors, ranging from smoking and high cholesterol to vision loss.
Experts say the latest French study underscores the urgent need for integrated mental and neurological health strategies, both for prevention and early intervention.
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