Mental Disorders Forecast Alzheimer’s Disease and Related Dementias in 1.7 Million New Zealanders

Neurodegenerative conditions, including Alzheimer’s disease and related dementias (ADRD), have an outsized impact on disability and loss of independence in older adults. As such, there is a growing need to identify modifiable risk factors for ADRD at the population level. We conducted a nationwide administrative-register study to investigate mental disorders as a potential preventable risk factor for later-life ADRD. Data were drawn from the New Zealand Integrated Data Infrastructure, a collection of whole-of-population administrative data sources linked at the individual level by a common spine. We identified all individuals born in New Zealand between 1928-1967 and followed them for three decades (N = 1,711,386; observation period = 1988-2018; age at baseline = 21-60 years). Diagnoses of mental disorders were ascertained from public-hospital records. Diagnoses of ADRD were ascertained from public-hospital records, mortality records, and pharmaceutical records. Individuals with a mental disorder were at elevated risk for developing Alzheimer’s disease and related dementias relative to those without a mental disorder. This prospective association was evident in both men and women, across age, and after accounting for pre-existing physical diseases. If associations are causal, ameliorating mental disorders could extend population healthspan and reduce the societal burden of neurodegenerative diseases.