Internalize at your peril: internalizing disorders as risk factors for dementia-cohort study

Few studies examined comorbid anxiety and depression's independent association with dementia. We assessed internalizing disorders as risk factors for dementia to avoid pitfalls inherent in separating anxiety and depression. Retrospectively designed prospective comparative cohort study using New Zealand's (NZ) National Minimum Dataset of hospital discharges. Hazards ratios (HRs), estimated from parametric survival models, compared the time to incident dementia after a minimal latency interval of 10 years between those with and without prior diagnosis of an internalizing disorder. A total of 47,932 patients aged 50-54 years were discharged from a publicly funded hospital events in NZ between 1988 and 1992. Of these, 37,631 (79%) met eligibility criteria, and incident dementia was diagnosed in 1594. Rates of incident dementia were higher among patients with an earlier diagnosis of internalizing disorders (572 vs 303 per 100,000 person years at risk (PYAR)). After adjustment for age, sex, ethnicity, and region, those with internalizing disorders were estimated to have a higher risk of developing dementia than those without (adjusted HR = 1.57, 95% CI 1.17-2.10). Females with an earlier diagnosis of internalizing disorders were estimated to have almost twice the risk of developing dementia (adjusted HR 1.80, 95% CI 1.25-2.59). Internalizing disorders affect one in five adults globally. Our findings suggest a significant increase in risk of dementia more than 10 years after the diagnosis of internalizing disorder.