Despite the recognized association between type 2 diabetes (T2D) and Parkinson's disease (PD), the implications of glycaemic variability for patients with PD are as yet unknown. For this reason, our study assessed the future risk of incident PD according to visit-to-visit fasting plasma glucose (FPG) variability, as calculated by standard deviation (FPG-SD), coefficient variance (FPG-CV) and variability independent of the mean (FPG-VIM).

Using the Korean National Health Insurance Service Health Screening Cohort, 131,625 Korean adults without diabetes were followed. They were divided into a midlife group (age<65 years) and an elderly group (age≥65 years) throughout a median follow-up of 8.4 years.

Adjusted hazard ratios (HRs) were calculated using multivariable Cox proportional-hazards analysis. In the midlife group, HRs for incident PD in the highest quartile of FPG variability (as measured by SD, CV and VIM) were 1.37 [95% confidence interval (CI): 1.09–1.73], 1.33 (95% CI: 1.06–1.68) and 1.35 (95% CI: 1.07–1.70), respectively, vs the lowest variability quartile group. However, while incident PD did not differ according to FPG variability in the elderly group, Kaplan–Meier curves of PD probability in the midlife group showed a progressively increasing risk of PD the higher the FPG variability. According to a multivariable adjusted model, every 1-SD unit increment in glycaemic variability was associated with a 9% higher risk of incident PD in the midlife group.

Increased long-term glycaemic variability may be a precipitating risk factor for developing PD in the midlife population without diabetes.