In this case, it appears to be the caffeine. Also, with these sorts of large studies, the amount is self-reported, so "a cup" is whatever the person reporting considers to be a cup, it's not some controlled amount.

Key Points

Question: Is long-term intake of caffeinated and decaffeinated coffee associated with risk of dementia and cognitive outcomes?

Findings: In this prospective cohort study of 131 821 individuals from 2 cohorts with up to 43 years of follow-up, 11 033 dementia cases were documented. Higher caffeinated coffee intake was significantly associated with lower risk of dementia. Decaffeinated coffee intake was not significantly associated with dementia risk.

Meaning: Higher caffeinated coffee intake was associated with more favorable cognitive outcomes.

[–] homesweethomeMrL@lemmy.world 8 points 6 days ago

Did they account for the coffee achievers? Maybe they threw off the curve.

Link for the kids

[–] Fmstrat@lemmy.world 1 points 4 days ago

Yea, "associated" does the work here. More research is needed into daily mental activities. It could simply be that those requiring more caffeine are also more stimulated day to day.