Tea drinking has already been linked with lowering the risk of heart disease, cancer and Parkinson's. Other research has shown that drinking tea on a regular basis for ten or more years may help improve bone density.

Now, Dutch researchers have carried out the study and found that it's the natural ingredients in tea which improve brain power and increase alertness, the latest edition of the 'Nutritional Neuroscience' journal reported.

For the study, the researchers looked at the effect of key chemicals found in tea on the mental performance of 44 young volunteers.

The effects of these ingredients, an amino acid called L-theanine -- which is also found in green tea -- and caffeine at levels typically found in a cup of tea, were compared with a dummy treatment.

The active ingredients significantly improved accuracy across a number of switching tasks for those who drank the tea after 20 and 70 minutes, compared with the placebo. The tea drinkers' alertness was also heightened, the study found.

Tea was also found to reduced tiredness among the subjects, who were aged under 40, say the researchers.

"The results suggest the combination helps to focus attention during a demanding cognitive task," they were quoted by the 'Daily Mail' as saying.

Dr Tim Bond, of the industry-backed Tea Advisory Panel, said the latest findings backed a previous study which showed drinking two cups of black tea "improves the ability to react to stimuli and to focus attention on the task in hand".

"Taken together, these two studies provide evidence that consumption of black tea improves cognitive function, in particular helping to focus attention during the challenge of a demanding mental task.

"As a result, all this new data adds to the growing science that drinking tea, preferably four cups of tea a day, is good for our health and well being."