Men and women with type 2 diabetes may face a significantly higher risk of developing Parkinson's disease later in life, new British research suggests.
The finding of a link followed the tracking of Parkinson's diagnoses among millions of diabetic and non-diabetic patients who use the National Health Service in England.
Study author Dr. Thomas Warner said that, after accounting for conditions that might mimic Parkinson's, the research showed that those with type 2 diabetes had a 32 percent greater risk of later developing the progressively debilitating neurological disorder.
Escalated risk was even more dramatic among younger diabetes patients, aged 25 to 44, who were found to face a fourfold greater likelihood of eventually developing Parkinson's, according to the report.
And adults with diabetes who had already developed diabetes-related health complications -- including damage to the retina, kidneys or nerves -- faced a 49 percent hike in their Parkinson's risk.
Nevertheless, Warner stressed, "it is vital to realize that, overall, the majority of diabetic patients do not develop Parkinson's disease."
Although the study could not prove a cause-and-effect relationship, Warner cited two possible reasons for a link between the two diseases.
First, he said, there could be "shared genetic predisposition to develop [both] type 2 diabetes and Parkinson's."
And then "there may be shared pathways in leading to development of diabetes and Parkinson's," he added. While the exact nature of such a connection remains unclear, Warner suggested it might involve the insulin production and glucose control problems that characterize diabetes.
"Unlike most tissues in the body, brain cells are almost totally reliant on glucose as a source of energy," Warner noted. "So if there is a problem in how insulin controls the use of glucose by cells, this may affect certain groups of brain cells selectively."
Warner is a professor of clinical neurology with the University College London Institute of Neurology, as well as the Queen Square Brain Bank for Neurological Disorder, both in London.
He and his colleagues published their findings online June 13 in the journal Neurology.
For their study, the investigators used data from the English "Hospital Episode Statistics" database to identify 2 million British patients newly diagnosed with diabetes from 1999 through 2011.
This group was then stacked up against 6 million British patients who had initially sought care during the same time frame for non-diabetes related issues, such as sprains, varicose veins, appendectomies or hip replacements.
The researchers found that just over 14,000 of the 2 million in the diabetes group were later diagnosed with Parkinson's, compared with about 21,000 of the 6 million others. That translated into a more than 30 percent greater risk for Parkinson's among those with diabetes, the researchers said.
Among diabetic patients 25 to 44 years old, 58 of over 130,700 people developed Parkinson's, compared with 280 out of nearly 2.6 million similarly aged non-diabetics. That translated into a fourfold greater Parkinson's risk among those with diabetes, the researchers said.
Drug regimens and smoking histories were not considered in the current analysis; nor were patients seeking diabetes care outside a hospital setting.
Dr. Michael Okun, medical director of the National Parkinson's Foundation, called the findings "not surprising, as the collective evidence from multiple studies has been converging on the idea of some link or association between Parkinson's and diabetes."
According to Okun, "There are many potential explanations for a link between the two diseases, but in younger patients, genetics likely plays a key role. In older patients, the degenerative process itself may disrupt brain-driven endocrine pathways, including those related to insulin and to sugar management."
Okun, who also serves as the chair of neurology at the University of Florida in Gainesville, said, "At this point the mechanisms are unknown, and will require careful research."
He said it's "important to stress that although diabetes drugs are currently candidates to treat or prevent Parkinson's disease, we are not recommending this approach until more compelling data is available."