Those writing in medical journal Genetics pointed out that scientists have known for years that those with diabetes had more chance of developing the disease, without really knowing why. But a new study of worms has shown that the Alzheimer’s gene does affect the way the body processes insulin.

Alzheimer’s is currently the leading cause of dementia, affecting 820,000 people in the UK alone. There are many drugs widely available that slow down the disease’s spread, but none can currently prevent it, despite scientists discovering the gene mutations in DNA running through families.

The American researchers were led by Professor Chris Li, and he said, “"People with type 2 diabetes have an increased risk of dementia. The insulin pathways are involved in many metabolic processes, including helping to keep the nervous system healthy."

Dr Marie Janson, director of development at Alzheimer's Research UK, told the BBC that they have cautiously welcomed the new research.

She said, "This early-stage study may provide an interesting clue to help scientists unravel how diabetes and Alzheimer's are linked, but questions still remain to be answered.

"As this research looked at the effects of a gene in worms, studies are now needed to discover whether the equivalent gene in people has the same effect, and exactly what mechanisms may be involved."