Type 2 diabetes increases the risk of developing Parkinson’s disease by nearly a third, according to a large retrospective U.K. study. The presence of complications and younger age at becoming a diabetic further strengthens this association.
The study, “Association between diabetes and subsequent Parkinson disease – A record-linkage cohort study,” was published in the journal Neurology.
Type 2 diabetes is a disease in which blood sugar levels are too high due to insufficient production of insulin — the hormone that helps move sugar into cells for energy — or to insulin resistance, meaning that cells do not use it appropriately.
Insulin resistance can reach the brain and induce severe changes in nerve cells, increasing the risk of Parkinson’s disease. It is also believed that abnormally high blood sugar promotes inflammation, which is also associated with Parkinson’s development.
Recent studies suggest these two diseases are linked. In fact, a therapy used for the treatment of diabetes — Byetta (exenatide) by AstraZeneca — was seen to improve Parkinson’s symptoms in a Phase 2 clinical trial (NCT01971242).
Researchers used a U.K. nationwide hospital database, with records covering 12 years (1999-2011), to compare the medical records of people admitted to the hospital for type 2 diabetes for a first time with those admitted for problems not related to diabetes (as a control group).
They searched the records of more than two million people (2,017,115) in the type 2 diabetes group and more than six million (6,173,208) in the control group for a later Parkinson’s diagnosis. In the diabetes group, 14,252 patients (0.71%) had a Parkinson’s diagnosis during a later hospital admission, compared with 20,878 people (0.34%) in the control group.
To determine the risk of developing Parkinson’s disease, researchers performed an extensive and thorough analysis to exclude diseases known to mimic Parkinson’s, and to adjust the data for age, gender, place of residency, frequency of hospital admission, and follow-up duration.
People with type 2 diabetes were found to have a 32% higher risk of a later diagnosis of Parkinson’s disease than those without diabetes. This relative risk was even greater — 49% — among patients with complications associated with type 2 diabetes, whereas those without complications had a 30% increased risk.
Notably, younger diabetes patients (ages 25 to 44) had an almost four-fold increased risk of developing Parkinson’s, compared to adults of similar ages without diabetes.
When looking at records of older diabetes patients, those 75 and older, the increased risk was 18% compared to a matched control group.
“Whether it is genetics that may play a role in the development of these diseases or they have similar pathways to development needs to be investigated further,” Thomas T. Warner, the study’s senior author, said in a press release.
Warner also noted that the link between these two diseases may affect future diagnosis and treatment. “Restoring the brain’s ability to use insulin could potentially have a protective effect on the brain,” he said.
The study had some limitations, such as researchers’ inability to adjust results for medication and smoking, and the possibility that the results cannot be generalized to the overall population of diabetic patients, since those included in the study might have had more severe forms of diabetes than patients diagnosed in a clinic.