Diabetes ‘increases the risk of Parkinson’s’

People who have type 2 diabetes are almost a third more likely to develop Parkinson’s disease than those without the illness, a study has found.

The risk increases almost fourfold if patients aged between 25 and 44 are diagnosed with diabetes, the researchers said.

Previous studies have suggested a link but this study, involving more than 2 million people, offers the most robust evidence yet that the conditions could be related.

It is thought that the link may be down to genes that predispose people to the conditions, with earlier research finding more than 400 genes linked to both Parkinson’s and diabetes.

The researchers said it could also be down to the effect of diabetes on insulin signalling in the brain. In type 2 diabetes, the body becomes resistant to insulin, necessary for converting glucose to energy. Brain cells are particularly reliant on glucose for energy.

The study, which involved a team from University College London, the University of Oxford and Queen Mary University of London, also found that the more complications from diabetes, the greater the risk of Parkinson’s.

‘‘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," the study’s lead author, Professor Tom Warner of UCL, said.

‘‘While the association is substantial, it’s still clear that most people with type 2 diabetes will not go on to develop Parkinson’s.’’

The research, published in the journal Neurology, used hospital records to follow 2,017,115 people with type 2 diabetes between 1999 and 2011, comparing them with 6,173,208 people without the disease.

Among those with diabetes, 14,252 had a diagnosis or were later diagnosed with Parkinson’s disease during a later hospital admission, compared with 20,878 in the comparison group.

After taking into account other conditions, such as age, sex and area, the team concluded that people with type 2 diabetes were 32 per cent more likely to have a subsequent diagnosis of Parkinson’s disease.

The team said the findings could help to advance treatment of the disease. Research last year suggested that a diabetes drug might also relieve Parkinson’s symptoms.

‘‘We’ve added to evidence that diabetes and Parkinson’s are linked, which in turn raises the possibility that they may respond to common therapies,’’ Dr Alastair Noyce, a coauthor of the most recent study, said.

Dr Beckie Port, research communications manager at Parkinson’s UK, said: ‘‘Understanding the link between these two conditions could be key to developing treatments that slow the course of Parkinson’s, something that no current treatments can do.’’ Repurposing drugs already used to treat diabetes ‘‘could speed up the delivery of new and better treatments’’.

Because it was a hospital-based study, it is possible that those diagnosed with diabetes may have had a more severe form of the disease than those diagnosed in a clinic.