A 2026 study found that people who reported drinking more caffeinated coffee had lower rates of dementia during follow-up; tea and caffeine intake showed similar patterns. Decaffeinated coffee was not associated with lower risk. But this was an observational study, not a trial: it cannot show that caffeine prevents dementia or that adding coffee would lower any one person’s risk.
What did the study find?
Published online in JAMA on February 9, 2026, the prospective cohort study followed 131,821 participants from two US studies: women in the Nurses’ Health Study and men in the Health Professionals Follow-up Study. Over as long as 43 years, researchers documented 11,033 dementia cases. They examined reported intake of caffeinated coffee, decaffeinated coffee, tea and caffeine, as well as cognitive outcomes. Read the JAMA study.
Participants in the highest quartile of caffeinated coffee intake had a dementia incidence of 141 cases per 100,000 person-years, compared with 330 in the lowest quartile. After adjustment, the hazard ratio was 0.82 (95% confidence interval, 0.76–0.89). This compares groups in the cohort; it is not evidence that coffee cuts an individual’s dementia risk by 18%.
Tea and caffeine intake showed similar associations with lower dementia risk. Decaffeinated coffee did not show an association with lower risk. The study also reported modestly better cognitive function in association with greater caffeinated coffee and tea consumption, though objective cognitive testing was limited to the Nurses’ Health Study cohort.
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What intake levels were associated with the lowest risk?
The dose-response analysis found the lowest associated risk around 2–3 cups of caffeinated coffee a day, 1–2 cups of tea a day, or 300 mg of caffeine a day. The study defined a cup as 8 ounces. At higher intake, the analysis did not show greater differences.
These are observed patterns, not recommended doses. The study did not assign people to consume these amounts, and it does not establish that starting or increasing caffeine intake would produce the same outcomes.
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Why the association is not proof of prevention
This was a prospective observational study: researchers tracked participants’ reported habits and health outcomes rather than randomly assigning caffeine consumption. Differences in lifestyle, health or other factors—measured imperfectly or not measured—could help explain the results. The large sample and long follow-up strengthen the evidence for an association, but they do not establish cause and effect.
- Population: Participants came from two cohorts of health professionals, so results may not generalize to everyone.
- Outcome measurement: Dementia status may have been misclassified, and the researchers could not assess Alzheimer disease dementia separately.
- Exposure: The findings concern reported beverage and caffeine intake; they are not a randomized comparison of what happens when someone changes their habits.
For those reasons, the study supports “associated with lower dementia risk,” not “prevents dementia,” “protects against Alzheimer’s,” or a personal risk-reduction promise.
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How does this fit with earlier evidence?
Earlier reviews were more uncertain, and their results should not be collapsed into a single consensus estimate: they examined different populations, exposure measures and outcomes.
| Evidence | Scope and result | What it says about certainty |
|---|---|---|
| 2020 systematic review | Across 61 eligible studies, 57 examined dementia risk or cognitive decline. Of those, 16 (28%) reported positive outcomes and 30 (53%) reported findings that depended on study characteristics. | The review described the overall evidence as inconclusive. Associations were more often positive for moderate intake (100–400 mg/day), coffee or green tea, and women; these patterns are not proof of benefit. Read the review. |
| 2024 cohort meta-analysis | 38 cohorts included 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 (95% CI, 0.87–1.02) and 0.94 for caffeine (95% CI, 0.70–1.25). | The authors rated dementia evidence for tea, coffee and caffeine as low certainty. They rated Alzheimer disease evidence as low certainty for tea and coffee and very low certainty for caffeine. Read the meta-analysis. |
| 2018 prospective-study dose-response meta-analysis | Eight studies included 328,885 people and 7,486 dementia cases. A one-cup-per-day increase in coffee was not significantly associated with dementia (RR 1.01, 95% CI 0.98–1.05) or Alzheimer disease (RR 1.01, 95% CI 0.95–1.07). | The analysis did not find a statistically significant association at that dose increment. Read the meta-analysis. |
The 2026 study adds substantial prospective evidence, including long follow-up and repeated dietary assessment, but it does not resolve the key limitation shared by observational evidence: association cannot establish that caffeine itself caused the difference.
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Should you drink more coffee to reduce dementia risk?
These findings are not a medical reason to begin drinking coffee, increase caffeine, or switch from decaffeinated coffee. They do not establish a preventive effect or a specific benefit for an individual. If you already choose caffeinated coffee or tea, the study offers an association to understand—not a guarantee about future health. No particular coffee brand, brewing method, supplement or caffeine product was tested.
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