Dementia risk in middle-aged patients with schizophrenia, bipolar disorder, and major depressive disorder: a cohort study of 84,824 subjects

All severe mental disorders, namely schizophrenia, bipolar disorder, and major depression, are associated with dementia. However, a head-to-head comparison study of severe mental disorders and dementia risk is lacking. This study was a retrospective analysis from Taiwan National Health Insurance Database. In the current study, we included 14,137, 14,138, and 14,137 patients aged 45–69 years diagnosed with schizophrenia, bipolar disorder, and major depressive disorder, respectively, between 2001 and 2009 and 42,412 matched controls. Four groups were age-matched based by age of identification. Any dementia, including Alzheimer disease and vascular dementia, was diagnosed from the identification date to the end of 2011. Alzheimer disease was more likely in patients with bipolar disorder (hazard ratio [HR]: 10.37, 95% confidence interval [CI]: 6.93–15.52) and major depression (HR: 8.92, 95% CI: 5.93–13.41) than in those with schizophrenia (HR: 4.50, 95% CI: 2.84–7.13) and in controls. The likelihood of developing vascular dementia during the follow-up period was greater in patients with schizophrenia (HR: 4.55, 95% CI: 3.14–6.59) and bipolar disorder (HR: 4.45, 95% CI: 3.13–6.31) than in those with major depression (HR: 3.18, 95% CI: 2.21–4.58) and in controls. However, the overlapped CIs indicated the non-significant between-category differences. There was an increased risk of Alzheimer disease and vascular dementia in all groups compared with controls. For Alzheimer disease risk was greater bipolar and depression compared with schizophrenia while for vascular dementia risk was greater for bipolar and schizophrenia compared with depression. Our findings may encourage clinicians to closely monitor the trajectory of cognitive function in middle-aged and elderly patients with schizophrenia, bipolar disorder, and major depressive disorder.