Whether or not the diabetes drug metformin has a similar effect on other people is not yet known.
Trials are under way to assess metformin’s potential as a therapy both for dementia and mild cognitive impairment, which can lead to Alzheimer’s.
Metformin is used to sensitise patients with type 2 diabetes to the hormone insulin. The disease develops when the body ceases to respond to insulin, causing a build-up of blood sugar.
Scientists at the Kaiser Permanente research institute in California examined almost 15,000 diabetes patients aged 55 and older who were starting single- therapy treatment with metformin or a range of other drugs.
Over a period of five years, those taking metformin were 20% less likely to develop dementia.
“These results provide preliminary evidence that the benefits of insulin sensitisers may extend beyond glycaemic [sugar] control to neurocognitive health,” said study leader Dr Rachel Whitmer.
“Research in animals suggests that metformin may contribute to the creation of new brain cells and enhance spatial memory.”
Dr Eric Karran of Alzheimer’s Research UK said: “We know that diabetes is a risk factor for Alzheimer’s, but the observation that metformin appears to be particularly linked to lower dementia risk suggests its effects could be independent of its ability to lower blood sugar.”
Meanwhile, online thinking and memory tests for Alzheimer’s disease have been called into question by a panel of experts.
Scientists led by Dr Julie Robillard, from the University of British Columbia, reviewed 16 online tests hosted on sites with up to 9m users.
They scored the tests on a reliability scale from one (very poor) to 10 (excellent). Twelve of the tests were rated as poor or very poor. In addition, every test had “poor” or “very poor” scores for ethical factors, which included consent and conflicts of interest.
The results were presented yesterday at the Alzheimer’s Association International Conference in Boston.
A spokesman from the Alzheimer’s Society said: “It is understandable that people sometimes might want to turn to the internet for help if they are worried about their health. But what this research shows once more is that people need to be careful when considering online tests for Alzheimer’s.
“Scientifically unsound tests could potentially give a false diagnosis while offering no emotional support, which could be devastating for the person carrying it out. If people are worried about their memory, or any cognitive problem, it is important that they go and see their GP.”