The prescription drug methotrexate, but not a similar drug called sulfasalazine, reduced dementia cases by 29% in people with the condition, the study found.
Using electronic health records from large existing studies of people in the UK, Spain Denmark and the Netherlands researchers looked at volunteers over the age of 50, diagnosed with rheumatoid arthritis.
They compared 486 volunteers with dementia against 641 without.
Researchers used a statistical approach to mitigate for any potential factors which would skew the results to work out the risk of dementia.
They found that taking methotrexate for longer than four years was linked to the lowest risk of dementia.
Dr Danielle Newby, from University of Oxford said: “Our research exploring the use of the anti-inflammatory drug, methotrexate, in real-world data sets finds 29% fewer dementia cases in patients with rheumatoid arthritis.
“Our work highlights the benefit of using existing information to identify drugs already on the market that may potentially be used to prevent dementia cases.
“The Covid-19 pandemic has been tough for researchers like me and while it’s a highlight to present at the Alzheimer’s Research UK Virtual Conference, I hope that future research like mine will be supported by investment in the field, as without it we risk losing momentum in our search for treatments.”
The findings were presented at Alzheimer’s Research UK’s 20th Annual Research Conference.
Dr Susan Kohlhaas, director of research at Alzheimer’s Research UK, said: “Methotrexate is a prescription drug and should only be used when prescribed by a doctor or qualified healthcare professional.
“As methotrexate is already a licensed anti-inflammatory prescribed to people with arthritis, and information already exists about its safety, understanding its potential benefit for brain health could help reduce dementia risk for many people.
“While we’re on the brink of the first disease-modifying treatments for diseases like Alzheimer’s, with nearly one million people living with dementia, we owe it to them to explore all possible approaches to prevent the condition in the first place.
“Research like this can give us vital clues about the mechanisms underlying dementia and may pave the way for preventative treatments in the future.”