An analysis of six different studies by the University of California researchers found drinking tea helped the brain to stay sharper.
The benefits of drinking as little as one to three cups a day in staving off mental decline are especially pronounced among women.
Scientists believe some compounds such as theanine found in tea could protect against Alzheimer's.
In one study, of almost 1,500 men and women in Singapore, drinking more than four cups a day cut the odds of memory failing by three-quarters, the 'Daily Mail' reported.
Even just one to three cups of tea a day had an effect, cutting the odds of cognitive decline by 43 per cent.
It is thought compounds in tea may protect against the poisons that ravage the brain in Alzheimer's. Possibilities include theanine, a plant chemical found only in tea and in mushrooms.
Experts in the US analysed several studies on the effect of caffeinated drinks on memory and mental alertness. The thousands of men and women who took part logged how often they drank tea or coffee and did a memory test that is used in the initial stages of diagnosing Alzheimer's disease.
Up to ten years later, they resat the test and any fall in score was noted.
The brain stayed sharper in those who drank tea in all the studies that included the drink, the journal Advances in Nutrition reported.
A study which tracked 4,000 Americans for almost eight years suggested tea to be of particular benefit to women.
Researchers who reviewed the studies said the weaker results for coffee mean caffeine is unlikely to be responsible for the cognitive benefits.