Skimming the study leaves some weird results.

- There's a sharp decrease in incidence between 2.5 drinks/day and 4.5 (3rd/4th quartile)

- Technically decaffeinated coffee actually had more dementia cases in the NHS cohort

- The highest decaf group is 1 drinks/day

- They didn't track the kinds of tea people were drinking (black, green, herbal)

- Drinking one cup of tea seems nearly as effective as 2.5 cups of coffee.

while it seems they were controlling for caffeine intake the tea vs coffee groups would have had wildly different intake with similar results.

also I couldn't tell if they tracked if the people drinking 40oz of coffee a day simply dropped dead before they could go crazy