Type 2 Diabetes Could Increase Risk, Speed Progression of Parkinson Disease

Alastair Noyce, PhD

While previous research has drawn links between glycemic control and type 2 diabetes to dementia and declining neurological health, a team from Queen Mary University of London claims to have uncovered evidence linking type 2 diabetes progression of Parkinson disease.

A systematic review and meta-analysis of data from 28 observational studies, results of the study suggest patients with type 2 diabetes saw their risk of developing Parkinson disease and presence of diabetes could be associated with increased progression of motor symptoms.

"This research brings together the results from many other studies to provide convincing evidence that type 2 diabetes likely affects not only Parkinson's risk, but also Parkinson's progression. There are many treatment strategies for type 2 diabetes, including prevention strategies, which may be re-purposed for the treatment of Parkinson’s,” said lead investigator Alastair Noyce, PhD, a clinical senior lecturer in the Preventive Neurology Unit at the Wolfson Institute of Preventive Medicine at Queen Mary University of London, in a statement.

With previous reviews and meta-analyses producing conflicting results, Noyce and colleagues sought to draw a clearer understanding of the relationship between type 2 diabetes and Parkinson disease. With this in mind, investigators designed their study to use data obtained from electronic databases including WebofScience, PubMed, Scopus, Ovid, and more. For the purpose of their analyses, investigators only included observational studies examining preceding type 2 diabetes and its effect on the risk of Parkinson disease or studies analyzing how diabetes was associated with the progression of Parkinson disease.

Investigators noted only English language articles were included and reviews, short surveys, books, and letters that reported no new data were excluded from the analysis. Investigators assessed progression of Parkinson disease using standard motor and cognitive scales. Additionally, progression per year was calculated to generate a standardized mean difference (SMD) for each study.

Using data from previous genome-wide association studies, investigators hope to perform two-sample Mendelian randomization, which would then be used to calculate causal estimates using the inverse-variance weighted (IVW) method.

The investigators’ initial search yielded 33,408 articles. After application of inclusion criteria, 28 were deemed eligible for inclusion in the meta-analyses. With these 28 articles, investigators performed 3 separate meta-analyses and systematic reviews. These assessed risk of Parkinson disease associated with type 2 diabetes specifically, risk of progression, and risk associated with any diabetes.

After analyses, pooled effect estimates indicated type 2 diabetes was associated with a 21% increase in risk of Parkinson disease (OR, 1.21; 95% CI, 1.07-1.36). The results also indicated type 2 diabetes was associated with faster progression of motor symptoms (SMD, 0.55; 95% CI, 0.39-0.72) and cognitive decline (SMD, -0.92; 95% CI, -1.50 to -0.34).

Using Mendelian randomization, investigators discovered evidence supporting a causal effect of diabetes on risk of Parkinson disease (IVW OR, 1.08; 95% CI, 1.02-1.14; P=.01). Investigators pointed out there was also some evidence of an effect on motor progression (IVW OR, 1.10; 95% CI, 1.01-1.20; P=.032) but no effect was observed when assessing cognitive progression.

This study, “Type 2 Diabetes as a Determinant of Parkinson’s Disease Risk and Progression,” was published in the Movement Disorders journal.