People with diabetes may have a heightened risk of developing Parkinson's disease, especially at a relatively young age, a new study finds.
Published in the journal Diabetes Care, the study adds to recent research linking diabetes to Parkinson's disease.
But neither this report nor the earlier ones prove that diabetes, itself, raises a person's risk of Parkinson's -- a disorder in which movement-regulating brain cells gradually become disabled or die.
Instead, researchers suspect that it's more likely diabetes and Parkinson's share some common underlying causes.
The new study looked at health insurance claims from more than one million Taiwanese adults -- including a little over 600,000 with diabetes.
Researchers found that over nine years, people with diabetes were more likely to be diagnosed with Parkinson's disease. They were diagnosed at a rate of 3.6 cases per 10,000 people each year, versus 2.1 per 10,000 among people without diabetes.
When the researchers factored in age, sex and certain other health conditions, they found that diabetes was still linked to an increased risk of Parkinson's -- especially at a relatively young age.
Among women in their 40s and 50s, those with diabetes had twice the risk of Parkinson's that diabetes-free women did.
The same was true among men in their 20s and 30s, though that was based on only a handful of Parkinson's cases: there were four cases among young men with diabetes, and two among those without diabetes.
Exactly what it all means is unclear, according to Drs. Yu Sun and Chung-Yi Li, who led the study.
But on average, people develop Parkinson's diagnosis around age 60, the researchers noted in an email to Reuters Health.
"Our findings tend to suggest a relationship between diabetes and early-onset Parkinson's disease," said Sun and Li, who are based at En Chu Kong Hospital and National Cheng Kung University in Taiwan.
That's in line with a study of Danish adults published last year, the researchers noted. Still, it's impossible to say for sure that diabetes, itself, is to blame.
One reason is that the current study had limited information, according to Sun and Li.
"Because our study was based on claims data," they said, "it lacks information on some of the known risk factors for Parkinson's disease, such as pesticide exposure."
Researchers have speculated on the potential reasons for the diabetes-Parkinson's link, and they suspect there might be certain biological mechanisms that contribute to both conditions.
One possibility is chronic, low-level inflammation throughout the body, which is suspected of contributing to a number of chronic diseases by damaging cells. There might also be a common genetic susceptibility to both diabetes and Parkinson's.
But even if people with diabetes have a relatively elevated risk of Parkinson's, it's still a low risk, Sun and Li pointed out.
In this study, there were fewer than four cases per 10,000 diabetic adults each year.
A recent U.S. study found a similar pattern: Of 21,600 older adults with diabetes, 0.8 percent were diagnosed with Parkinson's over 15 years. That compared with 0.5 percent of people who were diabetes-free at the study's start.
The researchers on that study said that people with diabetes should simply continue to do the things already recommended for their overall health -- like eating a well-balanced diet and getting regular exercise.
Sun and Li agreed with that advice. "There is no need for patients with diabetes to worry too much about the development of Parkinson's disease," they said.
More studies are needed, the researchers said, to understand why diabetes is related to a higher Parkinson's risk -- and what, if anything, can be done about it.
Diabetes arises when the body can no longer properly use the blood-sugar-regulating hormone insulin. Parkinson's occurs when 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.
Researchers say it's possible that something about diabetes -- like a problem regulating insulin -- might somehow contribute to Parkinson's. But that remains unproven.