People with diabetes may have a slightly increased risk of developing Parkinson's disease, a new study suggests.
The study of nearly 289,000 older US adults found that those with diabetes at the outset were more likely to be diagnosed with Parkinson's over the next 15 years.
Of 21,600 participants with diabetes, 172 (0.8%) were eventually diagnosed with Parkinson's. That compared with 1,393 cases (0.5%) among the 267,000 men and women who were diabetes-free at the study's start.
When the researchers accounted for other factors - such as age, weight and smoking habits, diabetes itself was linked to a 41% increase in the risk of future Parkinson's.
Whether diabetes is a cause of Parkinson's, and the reasons for any connection, are unclear, said senior researcher Dr Honglei Chen, of the US National Institute of Environmental Health Sciences.
"Really, the evidence at this time is very preliminary," Dr Chen said who reported the findings in the journal Diabetes Care.
Diabetes and Parkinson's disease would seem, at first, to be unrelated. But Dr Chen said the connection between diabetes and Parkinson's risk could mean that the two diseases share some underlying mechanisms.
One possibility, he speculated, is chronic, low-level inflammation throughout the body. Oxidation is another.
On the other hand, Dr Chen and his colleagues say, there might be something about diabetes –like a problem regulating insulin, that contributes to Parkinson's. But that remains to be proven.
A few large studies have looked at the diabetes-Parkinson's link before, with conflicting results.
The current study, Dr Chen said, included a larger number of people with Parkinson's. And unlike most past studies, it looked at the duration of people's diabetes.
In general, the higher Parkinson's risk was largely seen among people who'd had diabetes for more than 10 years before the start of the study.
That, Dr Chen said, supports the idea that diabetes came first, before Parkinson's, rather than the other way around.
But more studies, he said, are needed to understand why the connection exists, and what, if anything, can be done about it.
(Reuters Health, Amy Norton, March 2011)