Impact of type 2 diabetes on the development of dementia and death in Parkinson's disease

Background: Increasing evidence suggests that type 2 diabetes (T2DM) can influence the progression of Parkinson's disease (PD). However, it remains unclear whether T2DM increases the risk of progression to dementia and death in PD. Objective: This study aimed to investigate the impact of T2DM on the risk of developing dementia and death following a diagnosis of PD. Methods: We examined 158,962 individuals (aged 60 years or older) without PD or dementia using the Korean National Health Insurance Service (NHIS)-senior cohort database. A multi-state model was used to estimate the hazard ratios characterizing the effect of T2DM on the risk of PD, dementia, and death while adjusting for potential confounding factors. Results were analyzed according to age and sex. Results: T2DM increased the risk of development of PD (adjusted hazard ratio [aHR]: 1.26, 95 % confidence interval [CI]: 1.11–1.42), dementia (aHR: 1.31, 95 % CI: 1.24–1.39), or death (aHR: 1.58, 95 % CI: 1.52–1.65) compared to those without T2DM. However, after PD diagnosis, T2DM was not associated with progression to dementia (aHR: 1.09, 95 % CI: 0.96–1.48) and death (aHR: 1.10, 95 % CI: 0.85–1.42) although subgroup analysis showed an elevated risk for the progression from PD to dementia (aHR: 1.41 95 % CI: 1.06–1.89) in individuals under 70 years of age. Conclusions: T2DM increases the risk of PD, dementia, and death in the elderly population. However, its effect on the progression to dementia and death may occur independently of the onset of PD, despite significant age-related heterogeneity.