My parents drank iced tea all their lives. My dad was still sharp at 92 when he died. My mom was sharp until about 88 then slowly developed dementia. She was forgetful but knew all family until death at 93. She’d had TIA’s.

Billions of people the world over drink tea daily and I've never seen that correlated with dementia. Tea is an antioxidant and of course keeps sleepiness at bay. Anything in excess can be harmful (tea can be dehydrating or over stimulating). But I've never read or heard tea is a culprit in mental decline. Plus, I personally love it! Of course tea drinkers can grow old and have dementia. But I doubt there is any causation.

It is possible that "Tea drinking" isn't referring to the chemical effects of tea but the manner in which it was consumed in English society. As someone who enjoys relaxing with friends around a pot of hot tea, I can say that if I indulged in that activity daily, I'd get little done and could be accused of being a dullard.