According to a study sponsored in part by NIA and published in JAMA Psychiatry, mental illnesses early in life increase the risk of dementia and dementia occurring at a younger age. Researchers looked at the health records of 1.7 million New Zealanders over three decades and discovered significant correlations between various psychiatric illnesses and dementia types, including Alzheimer’s disease. These findings suggest that early interventions to treat mental problems such as anxiety or addictive behaviour will not only enhance the mental health of younger adults but also lessen the risk of dementia later in life if these connections are causal.
Depression has been found as a preventive risk factor for dementia in several studies. The implications of various mental disorders on dementia risk, as well as the prevalence of these diseases earlier in life and any connections with early-onset versus later-onset dementia, are less well known. Researchers reviewed New Zealand’s national health system’s hospitalisation records for 1.7 million people aged 21 to 60 years at the start of the study, tracking diagnoses for all mental disorders and any associated dementia from July 1988 to June 2018. Substance abuse, psychotic, mood, neurotic (i.e., anxiety), physiological disturbance, personality, developmental, behavioural, and unspecified diseases were all characterised by researchers.
A mental disorder was diagnosed in 3.8% of the study population, while dementia was diagnosed in 2%. The researchers discovered that people with a mental-disorder diagnosis were more than four times as likely as those without a mental condition to develop dementia. Notably, those with past mental versus physical disorders had a higher chance of dementia, which was comparable to the risk linked with the APOE4 gene, a well-known genetic risk factor for Alzheimer’s. The researchers also discovered that people with a past mental-health diagnosis developed dementia five years earlier on average than those without. Importantly, these correlations were discovered for all types of dementia and mental disorders, including psychosis, substance abuse, mood, neurotic, and self-harm disorders. Psychotic disorders, such as schizophrenia, were also linked to a higher risk of dementia than neurotic disorders, such as depression and anxiety, according to the study. Even after accounting for physical disease histories and socioeconomic risk variables, all of these outcomes were constant for men and women across all age groups.
This study has certain potential drawbacks, according to the researchers. The findings, for example, cannot be applied to other countries or healthcare systems. However, the researchers point out that several mental disorders, such as anxiety and depression, have been correlated to dementia in studies conducted in the United States and other countries. Less severe cases treated outside of the hospital or individuals who did not receive treatment were not followed, so the number of mental disorders or dementia cases in the study group may be higher than reported. Similarly, some of the study’s younger participants may have developed dementia after it ended. The findings of this study have major repercussions, including evidence that treating mental illnesses earlier in life may lower the chance of dementia later in life. Furthermore, these findings should drive further study into the shared and unique processes of dementia risk in psychiatric illnesses. Finally, their data support the inclusion of dementia-prevention methods in mental disorder therapy across the lifespan.
NIA grants AG032282, AG069939, AG049789, and P30-AG066589 helped fund this study in part. These initiatives are related to the Alzheimer’s and Related Dementias Research Implementation Milestones at the National Institutes of Health:
- Develop and test precise neuropsychological and behavioural evaluation approaches for detecting and tracking early clinical symptoms of Alzheimer’s disease and dementia caused by Alzheimer’s disease.
- In the absence of a cognitive problem, assessing the efficacy of screening for clinically significant cognitive impairment.
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