Caffeine -> Dementia

However, the two variables would be correlated if the causal arrow were reversed and dementia influenced the propensity to consume caffeine:

Caffeine <- Dementia

And we would also observe the correlation if a person's general health influenced both the propensity to consume caffeine and dementia risk:

Caffeine <- General Health -> Dementia

Since caffeine is a stressor, we would expect to see reduced consumption among people with reduced general health. But we would also expect increased dementia among that same group. So the relationships in the diagram immediately above are plausible and would give rise to a spurious correlation between caffeine consumption and dementia risk.

While studies can try to “control for confounding factors,” it’s easy to overlook or misunderstand the true causal relationships in play, causing spurious correlations. In other words, you can create false “causal” relationships through imperfect identification and control of confounding variables.

In short, take this article’s claims with a suitable dose of suspicion.

(1) https://jamanetwork.com/journals/jama/article-abstract/28447...

”After adjusting for potential confounders and pooling results across cohorts, higher caffeinated coffee intake was significantly associated with lower dementia risk (141 vs 330 cases per 100 000 person-years comparing the fourth [highest] quartile of consumption with the first [lowest] quartile; hazard ratio, 0.82 [95% CI, 0.76 to 0.89]) and lower prevalence of subjective cognitive decline (7.8% vs 9.5%, respectively; prevalence ratio, 0.85 [95% CI, 0.78 to 0.93]).”

So about 18% relative reduction. But if your risks are already low (e.g. active and healthy diet) the relative reduction is less impactful (e.g. 4% to 3.28%).

"Consumption of coffee and tea and the risk of developing neurodegenerative diseases: a cohort study in the UK biobank"

https://link.springer.com/article/10.1186/s12937-026-01291-0

Conclusions

"Excessive coffee consumption was significantly associated with an increased risk of all-cause neurodegenerative diseases and vascular neurodegenerative diseases. The results also showed that tea intake was associated with a reduced risk of all-cause neurodegenerative disease, vascular neurodegenerative disease, other neurodegenerative diseases, and VD. Moreover, coffee and tea had an interactive relationship with all-cause neurodegenerative diseases and AD, with specific combinations significantly associated with reduced risk of disease" onset.