Background
Type 2 diabetes (T2D) is an established risk factor for dementia. However, it remains unclear whether the presence of comorbidities could further increase dementia risk in diabetes patients.

Objectives
To examine the associations between cardiovascular and non-cardiovascular comorbidities and dementia risk in T2D patients.

Design
Population-based cohort study.

Setting
The UK Clinical Practice Research Datalink (CPRD).

Participants
489,205 T2D patients aged over 50 years in the UK CPRD.

Measurements
Major cardiovascular and non-cardiovascular comorbidities were extracted as time-varying exposure variables. The outcome event was dementia incidence based on dementia diagnosis or dementia-specific drug prescription.

Results
During a median of six years follow-up, 33,773 (6.9%) incident dementia cases were observed. Time-varying Cox regressions showed T2D patients with stroke, peripheral vascular disease, atrial fibrillation, heart failure or hypertension were at higher risk of dementia compared to those without such comorbidities (HR [95% CI] = 1.64 [1.59–1.68], 1.37 [1.34–1.41], 1.26 [1.22–1.30], 1.15 [1.11–1.20] or 1.10 [1.03–1.18], respectively). Presence of chronic obstructive pulmonary disease or chronic kidney disease was also associated with increased dementia risk (HR [95% CI] = 1.05 [1.01–1.10] or 1.11 [1.07–1.14]).

Conclusions
A range of cardiovascular and non-cardiovascular comorbidities were associated with further increases of dementia risk in T2D patients. Prevention and effective management of these comorbidities may play a significant role in maintaining cognitive health in T2D patients.