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NEW YORK (Reuters Health) - People with diabetes may have a slightly increased risk of developing Parkinson's disease, a new study suggests -- though the reasons for the link, researchers say, are far from clear.
The study, of nearly 289,000 older U.S. 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 percent) were eventually diagnosed with Parkinson's. That compared with 1,393 cases (0.5 percent) among the 267,000 men and women who were diabetes-free at the study's start.
When the researchers accounted for other factors -- like age, weight and smoking habits -- diabetes itself was linked to a 41 percent increase in the risk of future Parkinson's.
That, however, does not prove that diabetes is a cause of Parkinson's, and the reasons for the connection remain unknown, said senior researcher Dr. Honglei Chen, of the U.S. National Institute of Environmental Health Sciences.
"Really, the evidence at this time is very preliminary," Chen told Reuters Health.
People with diabetes, he said, should simply continue to do the things already recommended for their overall health -- eating a well-balanced diet and getting regular exercise.
Chen and his colleagues report the findings in the April issue of the journal Diabetes Care.
Diabetes and Parkinson's disease would seem, at first, to be unrelated.
Diabetes arises when the body can no longer properly use the blood-sugar-regulating hormone insulin. Parkinson's is a brain disease in which movement-regulating cells in the brain die off or become disabled, leading to symptoms like tremors, rigidity in the joints, slowed movement and balance problems.
But 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, which is suspected of contributing to a number of chronic diseases by damaging cells. Oxidation - the process fought by anti-oxidants - is another.
On the other hand, 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, 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, Chen's team found, 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, 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.
SOURCE: bit.ly/hrUWrc Diabetes Care, April 2011.