Middle-aged people who drink moderate amounts of coffee significantly reduce their risk of developing Alzheimer's disease, a study by Finnish and Swedish researchers showed Thursday.

"Middle-aged people who drank between three and five cups of coffee a day lowered their risk of developing dementia and Alzheimer's disease by between 60 and 65 per cent later in life," said lead researcher on the project, Miia Kivipelto, a professor at the University of Kuopio in Finland and at the Karolinska Institute in Stockholm.

The study, which was also conducted in cooperation with the National Public Health Institute in Helsinki and which was published in the Journal of Alzheimer's Disease this month, was based on repeated interviews with 1,409 people in Finland over more than two decades.

They were first asked about their coffee-drinking habits when they were in their 50s and their memory functions were tested again in 1998, when they were between 65 and 79 years of age.

A total of 61 people had by then developed dementia, 48 of whom had Alzheimer's, the researchers said.

"There are perhaps one or two other studies that have shown that coffee can improve some memory functions (but) this is the first study directed at dementia and Alzheimer's (and) in which the subjects are followed for such a long time," Kivipelto told AFP.

She said it remained unclear exactly how moderate coffee drinking helped delay or avoid the onset of dementia, but pointed out that coffee contains strong antioxidants, which are known to counter Alzheimer's.

Some studies have also shown that coffee helps protects the nerve system, which can also protect against dementia, she said, pointing out that yet other studies show that coffee protects against diabetes, which in turn is known to be linked to Alzheimer's.

"Going forward, researchers should try to nail down exactly what the protective elements in coffee consist in," Kivipelto said.

The Finnish-Swedish research results surfaced just a day after a separate study published by psychologists at Durham University showed a link between heavy coffee drinking and hallucinations.

"I guess this shows that you shouldn't exaggerate," Kivipelto said when asked about the British study, pointing out that her research showed "insignificant" benefits to drinking more than five cups of coffee a day when it came to protecting against dementia.

"Too much is simply too much," she said.