Daily tea consumption (green, black or oolong) was associated with a 50% reduced risk of cognitive decline and a 86% lower risk in people genetically predisposed (ApoE4 gene) for Alzheimer’s disease.
The mechanism for the cognitive benefit is unclear and may include catechins, theaflavins, thearubigins and L-theanine which are all anti-inflammatory and have antioxidant activity. However, caffeine itself cannot be ruled out as a contributing factor as well.
While this data is an association and does not prove causation, the data was adjusted for many different factors that affect health and it still found the 50% and 86% reductions. The health factors that were adjusted for in the analysis included age, gender, education, smoking, alcohol consumption, body mass index, hypertension, diabetes, heart diseases, stroke, depression, ApoE4, physical activity, social and productive activities, vegetable and fruit consumption, fish consumption, and daily coffee consumption.