A cup of coffee a day could keep Alzheimer's disease at bay, research suggests.

Scientists have shown a daily dose of caffeine helps protect the brain from the harmful effects of cholesterol, which is linked to the disease.

The most common cause of dementia, Alzheimer's affects 500,000 Britons - and 500 new cases are diagnosed each day.

Doctors can do little to stop the disease from taking its devastating course, so techniques which stop or delay its development could be of major benefit.

Researchers from the University of North Dakota in the U.S. looked at the effect of caffeine on the blood-brain barrier, a natural mechanism which prevents harmful substances passing from the blood into the brain.

Previous studies have suggested that high levels of cholesterol - present in fatty foods - cause leaks in the barrier. This leads to the destruction of brain cells seen in Alzheimer's.

In this study, …