People with diabetes may have a heightened risk of developing Parkinson's disease, especially at a relatively young age, a new study finds.
Published online in 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 disease.
Instead, researchers suspect that it's more likely the two diseases share some common underlying causes.
The new study looked at health insurance claims from more than one million Taiwanese adults – including more than 600,000 with diabetes.
More risk in diabetic women
Over nine years, people with diabetes were diagnosed with Parkinson's disease 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 Dr Yu Sun and Dr 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 Drs 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. (See Reuters Health story of April 15, 2011.)
Genetic susceptibility in diabetes and Parkinson’s
The researchers acknowledge that the current study had limited data.
"Because our study was based on claims data," Drs Sun and Li 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.
Parkinson’s still a low risk
But even if people with diabetes have a relatively elevated risk of Parkinson's, it's still a low risk, the two authors pointed out.
In this study, there were fewer than four cases per 10,000 diabetic adults each year. A recent US study found a similar pattern: Of 21,600 older adults with diabetes, 0.8% were diagnosed with Parkinson's over 15 years. That compared with 0.5% of people who were diabetes-free at the study's start.
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.
(Amy Norton, Reuters Health, April 2012)