Mental disorders linked to increased risk of dementia earlier in life

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According to a study funded in part by the NIA and published in JAMA Psychiatry. By analyzing the medical records of 1.7 million New Zealand citizens over three decades, the researchers found these associations for different psychiatric conditions and for all types of dementia, including Alzheimer’s disease. If these associations are causal, these results suggest that early interventions to treat mental disorders, such as anxiety or addictive behaviors, would not only improve the mental health of young adults, but could also reduce the risk of dementia later in life. life.

Several studies have identified depression as a preventable risk factor associated with dementia. However, less is known about the effects of other mental disorders on the risk of dementia, as well as whether these disorders occur earlier in life and whether they are associated with early-onset dementia versus early-onset dementia. late onset.

To determine whether having a mental disorder increases the risk of developing dementia, researchers looked at hospital records from New Zealand’s National Health System for 1.7 million people aged 21 to 60 in the beginning of the study and followed diagnoses for all mental disorders and any subsequent dementia. from July 1988 to June 2018. Researchers classified nine broad categories of mental disorders: substance use, psychotic disorders, mood disorders, neurotic (i.e., anxiety) disorders, physiological disorders, cognitive disorders, personality, developmental, behavioral and unspecified disorders.

Of the total study population, 3.8% of people were diagnosed with a mental disorder and 2% with dementia. Within these groups, the researchers found that people diagnosed with a mental disorder were more than four times more likely to develop dementia than those without a mental disorder. Notably, the increased risk of dementia was greater in people with a history of mental disorders compared to physical disorders, of a magnitude similar to the risk associated with APOE4 gene, a well-established genetic risk factor for Alzheimer’s disease. The researchers also found that, on average, people who had previously been diagnosed with a mental disorder developed dementia more than five years earlier than those who did not.

Importantly, these associations were found for all types of dementia, as well as for all types of mental disorders, including psychotic, substance abuse, mood, neurotic, and self-harm disorders. The analysis also indicated that psychotic disorders, such as schizophrenia, were associated with a higher risk of developing dementia than neurotic disorders, such as depression and anxiety. All of these results were consistent for men and women across all age groups, even after controlling for history of physical illnesses and socioeconomic risk factors.

The researchers recognize some potential limitations to this study. For example, the results cannot necessarily be generalized to other countries or health care systems. However, the researchers note that studies in the United States and other countries have also identified associations between certain mental disorders — such as anxiety and depression — and dementia. The researchers also acknowledge that the number of mental disorders or cases of dementia in the study population may be higher than reported because less severe cases treated outside of hospital or people who did not receive treatment were not followed. Similarly, some of the younger individuals in the study may have developed dementia after the study ended.

The results of this study have important implications, including evidence that treating mental disorders earlier in life can reduce the risk of developing dementia. Furthermore, these findings should inspire future research to identify common and unique pathways of dementia risk in different mental illnesses. Finally, these results suggest that psychiatric problems may be a harbinger of possible future cognitive decline and support the potential inclusion of dementia prevention strategies in the treatment of mental disorders across the lifespan.

This research was supported in part by grants from the NIA AG032282, AG069939, AG049789 and P30-AG066589.

These activities relate to the NIH Alzheimer’s Disease and Related Dementias Research Implementation Milestones:

  • 9.H“Initiate research programs to develop and validate sensitive neuropsychological and behavioral assessment measures to detect and monitor early clinical manifestations of AD and AD-related dementias.”
  • 9.N“Determining the value of screening for clinically relevant cognitive impairment in the absence of cognitive complaint.”

Richmond-Rakerd LS, et al. Longitudinal associations of mental disorders with dementia: 30-year analysis of 1.7 million New Zealand citizens. JAMA Psychiatry. 2022;79(4):333-340. doi:10.1001/jamapsychiatry.2021.4377.

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