WASHINGTON — A history of type 2 diabetes was associated with a 34% higher risk of new-onset Parkinson's disease in older men, but diabetes did not seem to cause Parkinson's.
Data from epidemiology studies have suggested a link between diabetes and Parkinson's disease (PD), but there have been few prospective studies of the association.
To evaluate the relationship between new-onset PD and diabetes, Ashley E. Smith, a medical student at Northeastern Ohio Universities, Rootstown, and colleagues reviewed data from 21,841 men aged 40–84 years who were enrolled in the Physicians' Health Study. Those with a history of PD at baseline, with type 1 diabetes or unknown diabetes status, and who developed dementia before PD were excluded. They reported the findings in a poster presentation at the annual meeting of the American Geriatrics Society.
They identified 423 diabetes cases at baseline, 1,987 incident cases of diabetes, and 556 cases of PD over a median follow-up of 23.1 years. Mean baseline age was 55 years for men with diabetes and 52 years for men without diabetes. Mean age for PD diagnosis was 73 years.
Diabetes was associated with an increased risk of PD, but the risk did not increase with the duration or severity of diabetes. Instead, after adjustment for multiple factors including age, smoking, alcohol use, body mass index, hypertension, physical activity, and high cholesterol, the risk of PD was greatest in those with a normal baseline body mass index, older age at onset of diabetes, and a shorter duration of diabetes.
In the proportional hazard model, a diagnosis of diabetes was clustered around the diagnosis of PD, which supports a biological link between the two conditions. “Dopaminergic neurons are involved in glucose regulation and extensive damage to these neurons might lead to impaired peripheral glucose metabolism,” the investigators wrote.
More studies are needed to determine whether the increased risk of PD in adults with diabetes is because of detection bias or an underlying biological mechanism.
The study was supported in part by grants from the National Cancer Institute and the National Heart, Lung, and Blood Institute, in Bethesda, Md.