"Caffeine appears to block several of the disruptive effects of cholesterol that make the blood-brain barrier leaky," said Dr Jonathan Geiger, who led the study.
"High levels of cholesterol are a risk factor for Alzheimer's disease, perhaps by compromising the protective nature of the blood brain barrier.
"Caffeine is a safe and readily available drug and its ability to stabilise the blood brain barrier means it could have an important part to play in therapies against neurological disorders."