It was first suggested in the 1960’s that people with type-2 diabetes are at increased risk for developing Parkinson's disease (PD) – and when they do develop PD, its progression is faster and often more severe. This may be due, in part, to an apparent relationship in the brain between dopamine, insulin resistance, and glucose control. Insulin is not only made in the pancreas, it’s also present in the brain – where it has been shown to impact dopamine levels.
Parkinson’s is generally believed by scientists to be caused by the loss of dopamine-producing neurons. Parkinson’s symptoms, such as slowness, rigidity, and tremor, typically develop after approximately 40-80% of these dopamine-producing neurons die.
Why does this matter? Currently, more than 30 million people in the United States have type-2 diabetes, and that number is growing. The lifetime risk of developing Parkinson's is also on the rise. In light of these trends, it would be valuable to know whether any specific type-2 diabetes medications might be associated with an increased or decreased risk for developing PD.
A 40-month cohort study of over 100,000 patients with diabetes (Brauer et al., 2020) published in the journal, Brain, titled “Diabetes medications and risk of Parkinson's disease” examined the association between type-2 diabetes medications and the risk of developing Parkinson’s. Using patient medical records, the study authors compared the risk of developing PD in patients diagnosed with type-2 diabetes who took the following oral diabetes medications in various combinations:
1) Thiazolidinediones (also called glitazones), like pioglitazone (Actos) or rosiglitazone (Avandia), which specifically target insulin resistance
2) Drugs, like albiglutide (Tanzeum) or dulaglutide (Trulicity), that mimick glucagon-like peptide-1 (GLP-1) a hormone that promotes insulin secretion, and
3) Dipeptidyl peptidase 4 (DPP4) inhibitors, which increase GLP-1 levels, and lead to insulin secretion and lowering of blood sugar levels
The control (comparison) group were those individuals prescribed any other oral combination therapy for diabetes, such as metformin and sulfonylureas.
A wide variety of sophisticated mathematical analyses were conducted – with age, gender, smoking status, body mass index (BMI), and other known diabetes risk factors taken into account.
- The rate of Parkinson’s disease was 36–60% lower in the people who took DPP4 inhibitors and/or GLP-1 receptor agonists.
- There was no evidence of any association between the use of glitazones and Parkinson’s disease.
- No other medication or combination of medications demonstrated any statistically significant effect.
What Does This Mean?
In this large population-based cohort study, taking the medications DPP4 inhibitors and/or GLP-1 receptor agonists was associated with a lower rate of Parkinson’s disease. Based upon these findings of the possible protective effect of these medications, further studies are warranted and are currently underway. However, it is also important to note that an association is not the same as a causation. There may be other factors associated with taking certain type-2 diabetes medications that influence Parkinson’s risk.
Additionally, as noted by the study authors, while the results of this study may be useful for clinicians to take into account when choosing oral medications for treating diabetes, these preliminary results, “[…]cannot inform on the usefulness of specific drug classes on the rate of progression of Parkinson’s disease after diagnosis, nor on their efficacy among patients with Parkinson’s disease in the absence of diabetes" (Brauer et al., 2020, p. 3075). In other words, it’s too soon to tell, but the next phase of their research is already underway, where hopefully more definitive answers will be found.
The Parkinson’s Foundation believes in empowering the Parkinson’s community through education. Learn more about PD and diabetes by visiting the below Parkinson’s Foundation resources, or by calling our Helpline at 1-800-4PD-INFO (473-4636) for answers to your Parkinson’s questions.