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Psychiatry
Do Psychiatric Disorders Increase the Risk for Dementia?
New research finds that major psychiatric disorders are linked to dementia risk.
Posted May 9, 2022 Reviewed by Devon Frye
Key points
- In a recent study, a history of a psychiatric disorder was associated with elevated risk of developing dementia.
- A history of psychiatric disorders increased the risk for Alzheimer's disease, while increasing the risk of developing other dementias even more.
- If dementia occurred, it began about 5.6 years earlier in those with a history of psychiatric disorder than in those without such history.
- Early identification and treatment of psychiatric disorders may help mitigate the risk.
An article published in JAMA Psychiatry by Leah Richmond-Rakerd and colleagues should be of interest to everyone with a history of any type of psychiatric disorder. These investigators analyzed 30 years of data to determine the association between various psychiatric disorders and the subsequent development of dementia. The results of their analyses indicate that all major psychiatric disorders are associated with a sizable increase in risk for developing Alzheimer's disease as well as other dementias.
The research team used data from New Zealand’s “Integrated Data Infrastructure” to conduct their study. This database contains de-identified health data for all individuals born in New Zealand. It provides a near-comprehensive longitudinal source of illness-related information.
All persons born in New Zealand between 1928 and 1967 and who lived in the country during at least part of a 30-year observation period between July 1988 and June 2018 were included in the study. This provided investigators with a population of over 1.7 million individuals, aged 21 to 60 years at baseline.
Psychiatric disorders were grouped into several categories: psychotic, substance use, mood, neurotic (including anxiety), and other mental disorders (including personality, developmental, behavioral, physiological disturbance [eating disorders, sleep disorders, etc.], and unspecified disorders). Individuals who did not seek treatment for psychiatric symptoms were classified in the group without psychiatric disorders.
During the 30-year observation period, 64,857 individuals (3.8 percent) were identified as having a mental disorder and 34,029 (2.0 percent) as having dementia. People who were diagnosed with dementia prior to an initial diagnosis of psychiatric disorder were excluded from analyses investigating the association between pre-existing psychiatric disorders and dementia risk.
Previously, these investigators found that psychiatric disorders are associated with evidence of premature aging as individuals mature to middle age. In the present study, the investigators found an overall 4-fold increased risk for developing Alzheimer's disease or other dementias in those with a prior history of psychiatric disorders. The increased relative risk for developing symptomatic Alzheimer's disease was 2.8; the increased risk for all other dementias was 5.9.
This pattern of increased relative risk was seen for both men and women and for all age groups. These increases in risk persisted after controlling for the presence of various physical conditions, including coronary heart disease, gout, chronic obstructive pulmonary disease (COPD), diabetes, cancer, and traumatic brain injury. Although risk was somewhat attenuated after controlling for socioeconomic conditions as measured by a neighborhood deprivation factor, it was still substantial at 2.85.
In addition, those with psychiatric disorders who eventually developed dementia did so on average 5.6 years earlier than those without mental illness.
When the research team conducted further analyses to establish relative risks of various types of psychiatric disorders on the subsequent development of dementia, they found significant increases in risk associated with each category of psychiatric disorder. These ranged from a low of 2.9 for neurotic disorders to a high of 6.2 for those with psychotic disorders.
Do the results from this study indicate that psychiatric illnesses actually cause dementia later in life? Not necessarily; association does not prove causality. The authors mention several possible mechanisms underlying these associations, including psychosocial stressors such as social isolation, poor health behaviors, and lower education often associated with psychiatric illness; shared genetic risks; neuroinflammation; and small vessel disease. In fact, it is possible that there is a mixture of reasons that vary with each illness type and with each individual.
If part of this association is, in fact, causal—i.e., a history of psychiatric disorders somehow leads to an increased risk of dementia—the authors suggest that prevention or successful early treatment of psychiatric disorders may decrease the risk. This is another important reason for research focused on discovering ways of preventing psychiatric illness and developing new treatments for these serious disorders.
This column was written by Eugene Rubin M.D., Ph.D., and Charles Zorumski M.D.
References
Richmond-Rakerd, L.S., D'Souza, S., Milne, B.J., Caspi, A., & Moffitt, T.E. (2022). Longitudinal associations of mental disorders with dementia: 30-year analysis of 1.7 million New Zealand citizens. JAMA Psychiatry. 79(4): 333-340.
