Self-reported diagnosis of mental disorders, psychological distress, and risk of incident dementia in New Zealand.

Objectives: With increasing prevalence of psychological distress and mental health disorders over recent decades, both globally and in New Zealand (NZ), it is important to understand their potential association with dementia.

Design: Cohort study SETTING & PARTICIPANTS: The NZ Health Survey from 2011/12 to 2018/19 was used to create a cohort and followed up until 31st March 2022. Incident cases of dementia were identified in routinely collected health data.

Measurements: Cox regression models calculated the hazard ratio for dementia for self-reported diagnoses of anxiety, depression, bipolar affective disorder, and Kessler K10 psychological distress score after adjustment for age and sex, and cardiovascular risk factors.

Results: 74,184 individuals aged ≥ 30 years were followed up for 452,867 person-years (mean duration of follow up 6.1 years), with 1963 (2.6 %) developing dementia. All three mental health disorders were associated with an increased hazard ratio of dementia, ranging from 1.31 (95 % CI 1.12-1.54) increased hazard for anxiety to a 2.69 (95 % CI 1.87-3.86) increased hazard for bipolar disorder. The increased dementia hazard associated with anxiety was no longer evident after adjusting for comorbid depression (HR 1.04 95 % CI 0.94-1.17). Higher K10 scores were associated with an increased dementia hazard of 2.19 (95 % CI 1.90-2.51) at the recommended score cut-off of 20.

Conclusions: This study demonstrates an increased dementia risk associated with mental disorders and psychological distress in NZ. Our findings reinforce the need for timely and appropriate management of mental health distress and disorders in NZ.