In recently published data from the ongoing UK Biobank study, a population based cohort, greater consumption of coffee and tea were both linked to a lower risk for stroke, dementia, and post-stroke dementia. Over 365,000 participants aged 50-74 had data available regarding their beverage consumption, and over a median follow-up of 11.35 years, 2.8% had a stroke and 1.4% developed dementia. After multivariate adjustment, a non-linear association was found between intake of these two beverages and risk; separately and combined, intake of coffee and tea was associated with a lower risk of stroke and dementia. Participants that consumed a combination of 2-3 cups of coffee with 2-3 cups of tea per day appeared to have the greatest risk reduction, approximately 30% lower for both stroke and dementia. The combination of coffee and tea was also associated with a 48% lower risk for post-stroke dementia, at a consumption level of 3-6 cups per day.
This cohort study did not address mechanisms of action, but previous studies generally have supported its findings, particularly for ischemic stroke, with speculation that many of the polyphenols, phenolics, catechins, flavonoids, etc. found in coffee and tea have antioxidant and anti-inflammatory effects, help with insulin resistance and endothelial function, and have an inhibitory effect on beta-amyloid aggregation. That combined consumption was associated with the greatest risk reduction suggests that there may be complementary polyphenols in these two beverages.