However, a study found that coffee drinkers saw no reduction in their risk, suggesting that antioxidant compounds in black tea might be the key.

A number of studies have already linked black tea and green tea to health benefits ranging from preventing heart disease to reducing the risk of some cancers.

With Britons among the most prolific tea drinkers, getting through 168 million cuppas every day, that should be good news.

However, although research on cells in the lab have suggested that compounds in tea called polyphenols may fight the plaques which cause Alzheimer's, few studies in humans have confirmed it.

Now, however, a study by scientists in Singapore has studied the lifestyle of 2,500 people aged 55 or over and recorded how much tea they drank. Each volunteer also underwent a test to measure their cognitive function, or the "fitness" of their brain.

Two years later, researchers found that those drinking the most tea were least likely to have suffered cognitive decline, an early sign of dementia.

Drinking two to three cups a day cut the risk of illness by around 55%, while in heavy tea drinkers -- those on six to 10 cups a day -- it was 63%.

Coffee drinkers, on the other hand, saw either no benefit or a tiny increase in their risk of dementia, according to a report in the American Journal of Clinical Nutrition. It is not known whether adding milk would reduce these effects as some studies suggest, but others say it has no influence.

It is believed that tea works its magic either through preventing oxidation, where cells are destroyed in the same way as rust rots a car, or by blocking the build-up of the brain deposits called plaques.

The researchers concluded:

"Because tea is cheap, non-toxic and widely consumed, it has huge potential in promoting cognitive health and perhaps delaying dementia." Alzheimer's and dementia affect an estimated 750,000 people in Britain, and the number is expected to more than double in the next 40 years as the population ages.

Earlier this week, a study suggested that a common drug to treat allergy may one day offer hope to Alzheimer's patients. It was shown to improve the memory of those in the early stages of the disease.

However, another study on a vaccine found that, although it reduced plaques, it did not stop the disease progressing.

This could be important as most research centres on how to prevent brain plaques from forming in the belief they block messages from flowing freely around the brain, triggering Alzheimer's.

From the July 21, 2008, Prepared Foods e-Flash