Background: Reduced glucose tolerance has been long recognized as a potential risk factor for Parkinson’s disease (PD), and increasing scrutiny is currently being placed on insulin resistance (IR) as a pathologic driver of neurodegeneration. However,

Source: High Prevalence of Undiagnosed Insulin Resistance in Non-Diabetic Subjects with Parkinson’s Disease – IOS Press

for comparison, prevalence of Diabetes in the general population:

Depending on age groups, global diabetes prevalence is about 5% for the age group 35-39 years, 10% for the age group 45-49 years, 15% for the age group 55-59 years, and close to 20% starting at age group 65-69 years. (1) Diabetes prevalence numbers are largely determined by people with type2 diabetes who comprise about 90% of the total population. These individuals are characterized by various degrees of relative insulin deficiency in conjunction with a wide spectrum of insulin resistance

its high – 20% suggesting much higher prevalence of IR, not sure if IR in PD is that much above normal