Diabetes and parkinson's
New analyses of both observational and genetic data have provided "convincing evidence" that type 2 diabetes is associated with an increased risk for Parkinson's disease.
The fact that we see the same effects in both types of analysis separately makes it more likely that these results are real - that type 2 diabetes really is a driver of Parkinson's disease risk.
The two analyses are reported in one paper published online March 8 in the journal Movement Disorders.
Several studies have looked at diabetes as a risk factor for Parkinson's but very few have focused on type 2 diabetes and, as this is such a growing health issue, we wanted to look at that in more detail,.
The researchers performed two different analyses: a meta-analysis of observational studies investigating an association between type 2 diabetes and Parkinson's; and a separate Mendelian randomization analysis of genetic data on the two conditions.
They found similar results in both studies, with the observational data suggesting type 2 diabetes was associated with a 21% increased risk for Parkinson's disease and the genetic data suggesting an 8% increase risk. There were also hints that type 2 diabetes might also be associated with faster progression of Parkinson's symptoms.
The pooled effect estimates showed that type 2 diabetes was associated with an increased risk for Parkinson's disease (odds ratio 1.21; 95% confidence intervals 1.07 - 1.36), and there was some evidence that type 2 diabetes was associated with faster progression of motor symptoms (standardized mean difference [SMD] 0.55) and cognitive decline (SMD −0.92).
The observational meta-analysis included seven cohort studies and two case-control studies, and these different types of studies showed different results in regard to the association between diabetes and Parkinson's. While the cohort studies showed a detrimental effect of diabetes on Parkinson's risk (OR, 1.29), the case-control studies suggested protective effect (OR, 0.51).
For the genetic analysis, the researchers combined results from two large publicly available genome‐wide association studies - one for type 2 diabetes and one for Parkinson's disease to assess whether individuals with a genetic tendency to type 2 diabetes had a higher risk of developing Parkinson's.
Results showed an increased risk for Parkinson's in those individuals with genetic variants associated with type 2 diabetes, with an odds ratio of 1.08 (P = .010). There was also some evidence of an effect on motor progression (OR 1.10; P = .032) but not on cognitive progression.
In the study, the authors also suggest that circulating insulin may have a neuroprotective role, whereas systemic and local insulin resistance can influence pathways known to be important in Parkinson's pathogenesis, including those that relate to mitochondrial dysfunction, neuroinflammation and synaptic plasticity.