History of Neurological or Psychiatric Conditions Increases the Likelihood of Developing More

Summary: People who suffer from a neurological or mental health condition are at increased risk of developing another disorder later in life. Parkinson’s disease patients are four times more likely to develop dementia, and those with mental health disorders were also at greater risk of developing dementia later in life.

Source: University of Waterloo

People living with neurological or psychiatric conditions may have an increased likelihood of having a second such condition in the future, and their sex influences their risk, according to new research. 

The study is Ontario’s largest, both in population size and length of time studied, and was also the first to examine the effect that being a man or woman has on the relationship between conditions. Researchers from the University of Waterloo and the Institute for Clinical Evaluative Science conducted the work with funding from the Neurodegenerative Disease Research Initiative (ONDRI).

“Globally, neurological and psychiatric disorders are leading causes of disability and death,” said Colleen Maxwell, a professor at the School of Pharmacy at Waterloo and lead author on the study. “Understanding which disorders or conditions are risk factors for, or early manifestations of, later disorders will help health-care providers and family provide proactive care for individuals living with these conditions.”

Maxwell and the study collaborators used provincial health databases to analyze data from more than five million Ontario residents aged 40 to 85 years. Over the course of 14 years, they examined the associations between pairs of particularly common neurological conditions­—such as dementia, Parkinson’s disease, or stroke—and psychiatric disorders like depression and anxiety.

They explored the link between these conditions in both directions, including investigating how the experience of previous stroke related to future risk of dementia and vice versa. In almost all cases, the researchers found that the rate of developing a second condition increased. For example, individuals with prior Parkinson’s disease had four times the rate of developing dementia, while those with prior stroke had more than double the rate of developing dementia.

This shows the shady outline of a man and a clock face
They explored the link between these conditions in both directions, including investigating how the experience of previous stroke related to future risk of dementia and vice versa. Image is in the public domain

They also found that having a psychiatric disorder previously was associated with an increased rate of experiencing dementia later. For some conditions, the risk of developing the second disorder remained for 10 years or more after the first. 

The team showed that women and men differed in their risk for developing a later condition after experiencing an earlier one. For example, comparing men and women who experienced an earlier stroke, women were more likely than their male counterparts to develop dementia later.

The researchers hope their work can inform not just the care that individuals with these conditions receive directly, but also the planning of the health system as a whole.

“We also hope to provide information for those designing medical, educational programs to ensure health-care providers are informed of and equipped to address these common comorbidities,” Maxwell said. 

Funding: The ONDRI supported the research through the Ontario Brain Institute.

About this neurology and mental health research news

Author: Ryon Jones
Source: University of Waterloo
Contact: Ryon Jones – University of Waterloo
Image: The image is in the public domain

Original Research: Closed access.
Incidence of neurological and psychiatric comorbidity over time: a population-based cohort study in Ontario, Canada” by Colleen Maxwell et al. Age and Aging


Incidence of neurological and psychiatric comorbidity over time: a population-based cohort study in Ontario, Canada


Comprehensive, population-based investigations of the extent and temporality of associations between common neurological and psychiatric disorders are scarce.


This retrospective cohort study used linked health administrative data for Ontarians aged 40–85 years on 1 April 2002, to estimate the adjusted rate of incident dementia, Parkinson’s disease (PD), stroke or mood/anxiety disorder (over 14 years) according to the presence and time since diagnosis of a prior disorder. Sex differences in the cumulative incidence of a later disorder were also examined.


The cohort included 5,283,546 Ontarians (mean age 56.2 ± 12.1 years, 52% female). The rate of dementia was significantly higher for those with prior PD (adjusted hazard ratio [adjHR] 4.05, 95% confidence interval [CI] 3.99–4.11); stroke (adjHR 2.49, CI 2.47–2.52) and psychiatric disorder (adjHR 1.79, CI 1.78–1.80). The rate of PD was significantly higher for those with prior dementia (adjHR 2.23, CI 2.17–2.30) and psychiatric disorder (adjHR 1.77, CI 1.74–1.81). The rate of stroke was significantly higher among those with prior dementia (adjHR 1.56, CI 1.53–1.58). Prior dementia (adjHR 2.36, CI 2.33–2.39), PD (adjHR 1.80, CI 1.75–1.85) and stroke (adjHR 1.47, CI 1.45–1.49) were associated with a higher rate of an incident psychiatric disorder. Generally, associations were strongest in the 6 months following a prior diagnosis and demonstrated a J-shape relationship over time. Significant sex differences were evident in the absolute risks for several disorders.


The observed nature of bidirectional associations between these neurological and psychiatric disorders indicates opportunities for earlier diagnosis and interventions to improve patient care.

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