Scientists say drinking a couple of teas or coffees daily links to a lower dementia risk.
A US study followed more than 130,000 people for up to 40 years.
Those drinking two to three coffees or one to two teas daily had a 15–20% lower risk.
Researchers also found slightly better cognitive performance among caffeinated coffee drinkers.
The findings appeared in the Journal of the American Medical Association.
The study cannot prove caffeine protects the brain.
Lead author Yu Zhang from Harvard University said the evidence fits known biology.
Coffee and tea contain caffeine and polyphenols that may reduce inflammation and oxidative stress.
No link appeared between decaffeinated coffee and dementia risk.
Experts say lifestyle factors may still explain part of the association.
Professor Naveed Sattar warned caffeine has both helpful and harmful effects.
Researchers stress exercise, healthy diet, and sleep remain key for brain health.
