Although the likelihood of having diabetes diagnosed is increased around the time Parkinson’s disease is identified, diabetes does not appear to increase the risk of Parkinson’s disease, according to findings published in Diabetes Care.

Some studies have found a positive association between diabetes and Parkinson’s disease, Dr. Jane A. Driver of Harvard Medical School, Boston, and colleagues point out. It has been suggested that diabetes might promote Parkinson’s disease through various pathways, including suppressing neurotransmitter levels, inflammation, oxidative stress, and cerebrovascular disease.

To investigate further, the researchers examined data from the Physicians’ Health Study involving 21,841 U.S. male physicians, who were followed for an average of 23.1 years.

The team reports that 423 subjects had the adult-onset type 2 diabetes at the beginning of the study and 1987 men reported developing diabetes during the study. A total of 556 participants reported having Parkinson’s disease during follow-up. The average age at diagnosis was 73.1 years.

Compared with non-diabetic men, those with diabetes had a 34-percent increased risk of Parkinson’s disease. Excluding subjects who developed vascular disease did not alter this association.

“The highest Parkinson’s disease risk was seen in individuals with short-duration, older-onset diabetes without complications,” Driver’s team reports.

The difference in diabetes incidence between Parkinson’s disease patients and matched control subjects was greatest during the year Parkinson’s disease was diagnosed and a few years before.

The findings “do not suggest that diabetes is a preceding risk factor for Parkinson’s disease,” the researchers conclude.

The clustering of diabetes diagnoses around the time of Parkinson’s disease identification could be a result of increased medical surveillance, a common underlying biological mechanism, or possibly some influence of Parkinson’s disease on diabetes risk.

SOURCE: Diabetes Care, October 2008.