A study that followed more than 51,000 people over 18 years has shown that people with Type 2 diabetes are more likely to develop Parkinson disease than those without diabetes.
The study, which enrolled Finnish men and women with no prior history of Parkinson disease, showed an 83% increased risk of developing the neurological disorder among people who had Type 2 diabetes at the start of the study. This increased risk held fast even when the researchers adjusted for body-mass index (BMI), blood pressure and cholesterol levels, education, physical activity, smoking, alcohol consumption, and coffee and tea consumption. Also, when people who had stroke or heart disease or used antipsychotic drugs—factors that can cause Parkinson-disease–like symptoms—were excluded, the link still remained between Type 2 diabetes and increased Parkinson disease risk.
Parkinson disease occurs when certain brain cells, which normally produce a chemical called dopamine, become impaired or die. Because dopamine helps control coordinated movement in the body, people who have Parkinson disease often experience tremor, slow movement, stiffness, and problems with balance. About 1.5 million Americans currently have Parkinson disease, which usually develops after age 65.
The researchers involved with the Finnish study, which is the first large study to evaluate the potential link between Type 2 diabetes and Parkinson disease over time, state that the biological mechanisms behind this link are currently not understood. However, there are some theories that may help explain the association. Past research has shown that higher body weight is associated with higher risk of Parkinson disease, and participants in this new study who had Type 2 diabetes had significantly higher BMIs at the beginning of the study than those who didn’t have diabetes. (The link between Type 2 diabetes and Parkinson disease, however, remained even when BMI was adjusted for.) Another potential explanation involves insulin; test tube and animal studies have shown that insulin may play a role in regulating dopamine action in the brain. Researchers have also hypothesized that the length of time a person has had Type 2 diabetes may be related to his Parkinson disease risk.
More research is needed to confirm this study’s findings and better understand how diabetes affects Parkinson risk. In the meantime, experts suggest that people with Type 2 diabetes keep their blood glucose levels under control, have regular medical checkups, and make sure to report any potential symptoms of Parkinson disease, such as tremors or trouble walking, to their doctors.