Patients with type 2 diabetes mellitus have an increased risk of developing Parkinson’s disease later in life, according to an investigation published online ahead of print June 13 in Neurology. The magnitude of risk is greater in younger patients and in patients with complications from diabetes.
Investigators have hypothesized an association between diabetes and the risk of Parkinson’s disease, but studies of the potential link have had conflicting results. Thomas T. Warner, MD, PhD, Professor of Clinical Neurology at University College London (UCL), and colleagues conducted a retrospective cohort study to examine this question anew.
Analyzing a Nationwide Hospital Database
The researchers reviewed English national Hospital Episode Statistics and mortality data collected between 1999 and 2011 and created a cohort of 2,017,115 patients who had been admitted for hospital care with a diagnosis of type 2 diabetes. They created a reference cohort of 6,173,208 patients without diabetes who were admitted for minor medical and surgical procedures. Conditions in this cohort included sprains, inguinal hernia, bruising, and hip replacement. People with Parkinson’s disease, ischemic cerebral infarction, vascular parkinsonism, drug-induced secondary parkinsonism, and normal pressure hydrocephalus were excluded from the study. Dr. Warner and colleagues created multivariable Cox proportional hazard regression models to estimate the risk of subsequent Parkinson’s disease.
Participants with diabetes had a greater risk of a subsequent diagnosis of Parkinson’s disease than patients in the reference cohort (adjusted hazard ratio [HR], 1.32). In subgroup analyses, the researchers found that the risk was substantially higher among patients between ages 25 and 44 (adjusted HR, 3.81) and those with complicated diabetes (adjusted HR, 1.49). Genetic factors may exert a relatively greater effect on younger people, and this difference may account for the increased risk among younger participants with diabetes, said the authors.
The adjusted HR of Parkinson’s disease was 1.40 in patients with diabetes between ages 65 and 74 and 1.18 in those age 75 or older. “The association in elderly patients may be the consequence of disrupted insulin signaling secondary to additional lifestyle and environmental factors causing cumulative pathogenic brain changes,” said Dr. Warner and colleagues.
No Adjustment for Potential Confounders
The large size of the database and the ability to exclude people with cerebrovascular disease and drug-induced and vascular parkinsonisms were among the study’s main strengths, according to the authors. Its weaknesses included an inability to adjust for potential confounders and the lack of clinical information about Parkinson’s disease ascertainment beyond routinely collected data.
The results could help researchers identify “new ways to treat or prevent the development of Parkinson’s disease, such as use of antidiabetes drugs to restore the brain’s insulin signaling,” said Dr. Warner. “A UCL-led study published last year found that a drug commonly used to treat diabetes shows promise in not only relieving Parkinson’s disease symptoms, but potentially altering the course of the disease itself. What we do not know is whether trying to treat people with type 2 diabetes better would reduce the risk of developing Parkinson’s disease.”