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Caffeinated coffee and tea were associated with lower dementia risk in a large, long-running study—but the study cannot show that caffeine prevents dementia. The result is a notable association, not a reason to start or increase caffeine intake as a medical measure.
What did the 2026 study find?
A prospective study published in JAMA on February 9, 2026, followed 131,821 participants from two US health-professional cohorts: women in the Nurses’ Health Study and men in the Health Professionals Follow-up Study. Over as many as 43 years, researchers documented 11,033 dementia cases. Higher reported intake of caffeinated coffee was associated with lower dementia risk; decaffeinated coffee was not. Tea and total caffeine intake showed similar patterns. [c001]
Participants in the highest quartile of caffeinated coffee intake had 141 dementia cases per 100,000 person-years, compared with 330 in the lowest quartile. The adjusted hazard ratio was 0.82 (95% confidence interval, 0.76–0.89). These are comparisons between groups in an observational study; they do not show that coffee would lower an individual’s risk by 18% if that person began drinking it.
How much caffeine was associated with the lowest risk?
The study’s dose-response analysis found the lowest associated risk around 2–3 cups of caffeinated coffee per day, 1–2 cups of tea per day, or 300 mg of caffeine per day. A cup was defined as 8 ounces. Higher intake did not show greater differences in risk. These observed levels are not medical recommendations, and beverage caffeine content varies.
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Why doesn’t this prove caffeine prevents dementia?
The researchers observed what participants reported consuming and compared it with later outcomes; they did not randomly assign people to drink caffeinated coffee, decaffeinated coffee, tea, or no caffeine. Differences in lifestyle, health, or other factors may help explain the association, even after statistical adjustment. The study therefore cannot establish that caffeine caused the lower risk.
- Population: Participants were health professionals in two US cohorts, so the findings may not apply equally to other populations.
- Outcome measurement: Dementia status may have been misclassified, and the authors could not assess Alzheimer disease dementia separately.
- Cognitive testing: Objective cognitive testing was limited to the Nurses’ Health Study cohort.
The size and long follow-up make the findings important, but they do not remove these limits or establish a preventive effect. JAMA study
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How does this fit with earlier evidence?
Earlier reviews were less conclusive, and their results should not be collapsed into one consensus number: they combined different populations, exposure measures, outcomes, and methods.
| Evidence | Scope and result | What it adds |
|---|---|---|
| 2020 systematic review | Among 61 eligible studies, 57 examined dementia risk or cognitive decline. Of those, 16 (28%) reported positive outcomes and 30 (53%) reported findings dependent on study characteristics. | The review called the overall evidence inconclusive. Results were more often positive for moderate intake (100–400 mg/day), coffee or green tea, and women; these study counts are not proof of benefit. [c002] |
| 2024 cohort meta-analysis | 38 cohorts, 751,824 participants, 13,017 dementia cases, and 17,341 Alzheimer disease cases. For dementia, highest-versus-lowest category pooled relative risks were 0.84 for tea (95% CI, 0.74–0.96), 0.95 for coffee (0.87–1.02), and 0.94 for caffeine (0.70–1.25). | The authors rated dementia evidence low certainty for tea, coffee, and caffeine; Alzheimer disease evidence was low certainty for tea and coffee, and very low certainty for caffeine. [c003] |
| 2018 dose-response meta-analysis | Eight prospective studies included 328,885 people and 7,486 dementia cases. Per one-cup/day increase in coffee, the relative risk was 1.01 for dementia (95% CI, 0.98–1.05) and 1.01 for Alzheimer disease (0.95–1.07); neither association was statistically significant. | This earlier analysis did not find a significant linear association per additional daily cup. [c004] |
The 2026 study adds substantial prospective evidence, including separate findings for caffeinated and decaffeinated coffee, but does not settle whether caffeine itself prevents dementia.
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Should you drink coffee or tea to reduce dementia risk?
The study does not justify starting caffeine, increasing your intake, or treating coffee or tea as dementia prevention. If you already choose these beverages, the findings describe an association at moderate intake levels; they do not establish a health benefit for you personally. No specific brand, roast, brewing method, supplement, or caffeine product was tested.
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