Now it is hoped further research could help improve treatments for both conditions, although experts are currently at a loss to explain the relationship between them.
Tom Warner, Professor of Clinical Neurology at University College London, who authored the study, said yesterday: “We can now say more definitely that there is a link between diabetes and Parkinson’s, but we need to do more research to understand the relationship, whether it’s due to genetics, the effect of diabetes on the brain, or both.”
Parkinson’s is a long-term degenerative brain disease characterised by involuntary shaking, while in Type 2 the body resists insulin, necessary for converting glucose into energy.
As brain cells are particularly reliant on glucose for energy, it has long been speculated the two diseases could be linked.
The study by UCL, the University of Oxford and Queen Mary University of London followed more than two million people diagnosed with Type 2 between 1999 and 2011. None had a Parkinson’s diagnosis.
They were studied alongside a comparison group of more than six million people without Type 2.
Among the people with diabetes 14,252 had a diagnosis of Parkinson’s disease during a later hospital admission, compared with 20,878 in the comparison group.
Experts found Type 2 sufferers were 32 per cent more likely to have a subsequent diagnosis of Parkinson’s.
The link was strongest among those aged between 25 and 44 and people with more complications from diabetes. Experts say the link could be due to a shared genetic predisposition to both conditions.
Type 2 now affects one in 10 British adults.
The findings could now help advance treatment for Parkinson’s.
Dr Beckie Port, of Parkinson’s UK, said: “Understanding the link between these two could be key to developing treatments that slow the course of Parkinson’s, something that no current treatments can do.”
Kathryn Kirchner, of Diabetes UK, said the study “does not show that Type 2 causes Parkinson’s. We would need further research to confirm whether these conditions are related and then work out the genetic or biological processes that could be behind the link.”
The research is published in Neurology, the medical journal of the American Academy of Neurology.