A lay summary by Louise Heywood, reviewed by Dr Tom Payne and a Parkinson’s disease lay panel
Background
• Parkinson’s disease is a condition with many facets, but the most commonly known are the effects it has on people’s movement and balance. This is caused by a loss of brain cells in a small area of the brain that produces dopamine – essential to normal brain activity.
• Type 2 Diabetes (T2DM) causes increased levels of sugar in the bloodstream, leading to fatigue, excessive urination, and problems with eyesight, amongst other things. Recently there has been growing interest in potential links between these two conditions. Several of the more serious diabetic complications, such as kidney disease and heart disease, have been shown to increase the likelihood of developing Parkinson’s disease.
As such, the links between these two illnesses represent an important area of research.
Why is the study important?
The loss of brain cells begins many years before people with Parkinson’s develop symptoms. Current treatments work to improve symptoms, but cannot prevent the loss of more brain cells, making effective treatment difficult. People with T2DM tend to be diagnosed at a younger age than when people will develop the symptoms of Parkinson’s. If there is a link between T2DM and a future diagnosis of Parkinson’s, then careful monitoring for early symptoms of Parkinson’s in people with T2DM could result in an earlier diagnosis of Parkinson’s and therefore more successful symptom management, particularly as we move towards researching treatments that can slow Parkinson’s progression.
What did the authors do and how did they do it?
The authors used data from the Korean National Health Insurance Service (NHIS), which holds healthcare data for the majority of the Korean population, including most medical information and including drug prescription records. They selected people with T2DM who were aged 40 or over and had undergone annual health examinations provided by the NHIS. These people were followed for an average of 7 years, and any incidents of a diagnosis of Parkinson’s were recorded. The researchers created a score to measure the severity of T2DM in each individual. This score combined components such as the duration of their diabetes, their fasting (pre-breakfast) blood sugar levels, the number of diabetic drugs they were taking and specifically whether they needed insulin to treat their diabetes. The researchers also looked at the effects of age, smoking and weight on risk of developing Parkinson’s. People for whom data was missing, or those who had been diagnosed with Parkinson’s prior to enrolment in the study were excluded, as were those diagnosed within the first year of follow-up.
What are the results?
Each component measured was associated with an increased risk of Parkinson’s, for example people who need insulin to manage their diabetes were more likely to develop Parkinson’s than those who did not. The risk increases with the number of components each person has – someone who requires insulin, has had diabetes for over 5 years, and has kidney disease is 55% more likely to develop Parkinson’s than someone who had none of the measured components. When the researchers looked at the association between T2DM and PD in specific subgroups, they found that age further increases the T2DM risk of developing Parkinson’s, with those aged between 45-60 years of age at greater risk, while smoking and weight had no effect on the risk. The risk of developing Parkinson’s was also highly increased for people with T2DM and chronic kidney disease compared to those without. Interestingly for both very low and very high fasting blood sugar levels there was a higher risk of PD, indicating that control of blood sugar levels may be important in the development of Parkinson’s disease.
What do the finding mean going forward for people with the disease?
While this study only looks at the Korean population, similar results have been reported by studies in other countries (Schernhammer et al., 2011), suggesting the link between type 2 diabetes and Parkinson’s disease may be of great importance. As Parkinson’s disease is typically diagnosed after significant loss of brain cells, identifying predisposing conditions means there can be greater vigilance for early PD symptoms. People with Type 2 diabetes will have regular medical check-ups, meaning they could benefit from greater ‘medical surveillance’ with doctors being on the look-out for any early PD symptoms in people more likely to develop the condition, leading to earlier diagnoses and better outcomes for people with Parkinson’s disease.
This study can be found at https://www.nature.com/articles/s41531-023-00462-8
Paper title A Nationwide Cohort Study on Diabetes Severity and Risk of Parkinson Disease
Author list Han, K., Kim, B., Lee, S. H. and Kim, M. K.
Publication details including date of publication. January 2023, npj Parkinson’s Disease 9(11) https://doi.org/10.1038/s41531-023-00462-8