Risk of Subsequent Dementia Among Patients With Bipolar Disorder or Major Depression: A Nationwide Longitudinal Study in Taiwan

Abstract Background Both major depression and bipolar disorder are associated with an increased risk of developing dementia. However, the differential risk of dementia between major depression and bipolar disorder is rarely investigated. Methods Using the Taiwan National Health Insurance Research Database, a total of 2291 patients aged ≥55 years (major depression: 1946 and bipolar disorder: 345) and 2291 age-and sex-matched controls were enrolled between 1998 and 2008, and followed to the end of 2011. Participants who developed dementia during the follow-up were identified. Results Both patients with bipolar disorder [hazard ratio (HR) 5.58, 95% confidence interval (CI) 4.26–7.32] and those with major depression (HR 3.02, 95% CI 2.46–3.70) had an increased risk of developing dementia in later life, after adjusting for demographic data and medical comorbidities. The sensitivity tests after excluding the 1-year (bipolar disorder: HR 4.73, 95% CI 3.50–6.35; major depression: HR 2.62, 95% CI 2.11–3.25) and 3-year (HR 3.92, 95% CI 2.78–5.54; HR 2.21, 95% CI 1.73–2.83, respectively) follow-up duration also revealed consistent findings. Furthermore, patients with bipolar disorder were associated with an 87% increased risk (HR 1.87, 95% CI 1.48–2.37) of subsequent dementia compared with patients with major depression. Conclusions Midlife individuals with bipolar disorder or major depression were associated with an elevated risk of developing dementia in later life. Further studies may be required to clarify the underlying mechanisms among major depression, bipolar disorder, and dementia, and to investigate whether prompt intervention may decrease this risk.