The finding comes from a Japanese study published in The American Journal of Clinical Nutrition.
The study included about 1,000 Japanese people aged 70 and older. Participants took tests of mental status including memory, orientation, ability to follow commands, and attention. They also told the researchers how often they drank beverages including green tea.
Those who reported drinking the most green tea were least likely to show cognitive impairment, based on their test scores, write Shinichi Kuriyama, MD, PhD, and colleagues.
Kuriyama works in the department of public health and forensic medicine at Tohoku University's medical school in Sendai, Japan.
How Much Green Tea Does It Take?
Drinking at least two daily cups of green tea was tied to the lowest risk of cognitive impairment in Kuriyama's study.
Compared with people who drank a cup of green tea up to three times weekly, those who drank two or more daily cups of green tea were 54% less likely to have test scores in the range of cognitive impairment.
Drinking green tea a little less often wasn't bad. People who drank a cup of green tea four to six times per week were 38% less likely to show cognitive impairment than those drinking green tea less than three times weekly.
Coffee, black tea, and oolong tea didn't show the same results. Green tea is a popular drink in Japan. More than seven in 10 participants reported drinking at least two cups of green tea daily.
Reading the Tea Leaves
The study doesn't prove that green tea deserves the credit for the elders' sharp minds.
The researchers didn't ask anyone to change their tea consumption for the study's sake. Instead, they checked test scores and tea habits.
Data was only gathered once. So it's not clear if participants' tea habits had lasted a lifetime or if their test scores changed over time.
Kuriyama's team considered factors linked to cognitive impairment, including diabetes, smoking, and advanced age. They also adjusted for potentially helpful habits, such as physical activity, social ties, consumption of fish and vegetables, and self-reported overall health.
Even after considering all those factors, high consumption of green tea was still associated with a lower risk of cognitive impairment, the study shows.
"To our knowledge, this is the first study to examine the association between consumption of green tea and cognitive function in humans," Kuriyama's team writes.
They note that natural compounds in green tea -- especially a chemical called EGCG (epigallocatechin-3-gallate) -- have shown promise in experiments on brain diseases in animals.
However, something else about green tea might help the brain, the researchers write.
For instance, people in Japan often socialize over green tea. Socializing could be good for the brain, note Kuriyama and colleagues.
They add that healthy people might be more likely to drink green tea. If so, those people would have a built-in brain advantage because of their general good health.