Decaf coffee showed no similar protective association, suggesting caffeine as the likely active factor.

A large prospective cohort study of 131,821 participants from the Nurses’ Health Study and Health Professionals Follow-Up Study finds that moderate caffeinated coffee and tea intake is associated with reduced dementia risk, slower cognitive decline, and preserved cognitive function.

The authors emphasize that the findings are observational and show correlations, not causation, with a modest protective effect and a sweet spot of about two to three cups of coffee or one to two cups of tea daily.

Limitations include reliance on observational data and potential unmeasured confounding factors despite the prospective design.

Experts noted in commentary that observational design cannot prove causation, potential confounding factors, reliance on self-reported diagnoses, and limited generalizability due to the study population of health professionals.

Leading authors reiterated that the findings show associations rather than causation; benefits may be influenced by other factors and by self-reported data, with limited generalizability from a homogeneous group.

Experts caution that results do not prove brain protection and highlight limitations such as reliance on self-reported data and a relatively uniform study population.

The study suggests a possible protective link but calls for further research to confirm causality and understand underlying mechanisms.

The study was published in JAMA and led by Dr. Yu Zhang from the Harvard TH Chan School of Public Health.

Key co-authors include Daniel Wang and Yu Zhang, with collaboration among Mass General Brigham, Harvard T.H. Chan School of Public Health, and the Broad Institute of MIT and Harvard; findings appear in JAMA (2026) with DOI 10.1001/jama.2025.27259.

Benefits were strongest among participants 75 or younger and persisted even in high genetic risk groups, though causality remains unproven.

More work is needed to determine causality and to understand confounding factors such as overall lifestyle, caffeine metabolism, and beverage additives.