DRINKING two cups of coffee a day could reverse the effects of Alzheimer's disease.

Researchers say they have uncovered evidence that caffeine not only helps to stave off the disease but can treat it.

The results have prompted calls for more research.

Neuroscientist Dr Gary Arendash said: "The new findings provide evidence that caffeine could be a viable treatment for established Alzheimer's disease and not simply a protective strategy.

"Caffeine is a safe drug for most people. It easily enters the brain and it appears to directly affect the disease process."

Previous studies have suggested that moderate amounts of caffeine can protect against memory loss.

In the new study caffeine was put in the drinking water of mice.

The amount of a key protein linked to Alzheimer's was halved in their brains, and the mice developed better memories and quicker thinking.

To get an equivalent dose of caffeine - 500 milligrams - humans would have to drink five eight ounce cups of ordinary coffee a day, or two cups of strong 'coffee shop' coffee, 14 cups of tea, or 20 cola drinks.

The study was carried out at the Florida Alzheimer's Disease Research Centre, in Tampa.

Director Dr Huntington Potter said: "These are some of the most promising Alzheimer's mouse experiments ever done showing that caffeine rapidly reduces beta amyloid protein in the blood, an effect that is mirrored in the brain, and this reduction is linked to cognitive benefit."

He said consuming 500mg of caffeine a day would present no problems for most people - although people with high blood pressure or women who are pregnant should avoid too much.

Rebecca Wood from the Alzheimer's Research Trust said: "We need to do more research to find out whether this effect will be seen in people. With no cure yet, research into treatments that could help people with Alzheimer's is vital."

Neil Hunt from the Alzheimer's Society said: "Much more research is needed to determine whether drinking coffee has the same impact in people."

Alzheimer's is the most common form of dementia and affects around 700,000 people in Britain.

That figure is expected to double by 2025, costing the country £17bn a year.