Drinking 2–3 cups of caffeinated coffee or 1–2 cups of tea daily was linked to an 18% lower risk of dementia over a 43-year study of more than 131,821 participants, according to research published in JAMA by scientists from Mass General Brigham, Harvard T.H. Chan School of Public Health, and the Broad Institute of MIT and Harvard.
The study drew on data from the Nurses’ Health Study and the Health Professionals Follow-Up Study, tracking participants for up to four decades with repeated dietary evaluations, dementia diagnoses, and cognitive performance assessments. Of the full cohort, 11,033 individuals developed dementia during the follow-up period.
Beyond reduced dementia incidence, participants with higher caffeinated coffee intake reported lower rates of subjective cognitive decline — 7.8% versus 9.5% among those who rarely or never drank it — and performed better on objective cognitive tests.
Caffeine Appears Central to the Effect
Decaffeinated coffee showed no comparable association, while tea drinkers saw similar patterns to coffee drinkers. Researchers say this points to caffeine as a likely contributing factor, though they caution that the mechanisms are not yet confirmed. Coffee and tea also contain polyphenols, compounds thought to reduce inflammation and limit cellular damage associated with cognitive decline.
Benefits did not diminish for people genetically predisposed to dementia, and higher caffeine intake beyond the identified optimal range did not appear to cause harm — it simply produced comparable rather than greater benefits.
“When searching for possible dementia prevention tools, we thought something as prevalent as coffee may be a promising dietary intervention — and our unique access to high quality data through studies that has been going on for more than 40 years allowed us to follow through on that idea,” said senior author Daniel Wang, MD, ScD, associate scientist at Mass General Brigham and assistant professor at Harvard Medical School.
A Single Piece of a Larger Puzzle
Wang was direct about the limits of the findings. “While our results are encouraging, it’s important to remember that the effect size is small and there are lots of important ways to protect cognitive function as we age,” he said. “Our study suggests that caffeinated coffee or tea consumption can be one piece of that puzzle.”
The research addresses a known gap in earlier work on coffee and brain health: most prior studies were shorter and captured dietary habits at only one or two points in time, making long-term patterns difficult to assess. The NHS and HPFS datasets allowed for repeated dietary evaluations across decades, offering a more stable picture of habitual consumption.
Dementia prevention has grown as a research priority partly because existing treatments offer only modest benefits once symptoms appear, pushing scientists toward lifestyle and dietary factors that may delay or reduce onset.
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