☕ Harvard Study Reveals Drinking Coffee and Tea Reduces the Risk of Dementia: The Exact Amount You Should Consume

Research published in JAMA followed more than 130,000 people for 43 years and confirms that caffeine is the key compound in cognitive protection

📅 April 7, 2026 | ⏱️ Reading Time: 7 minutes | 🏷️ Neuroscience · Nutrition · Prevention

Boston, USA — For decades, millions of people have started their mornings with a cup of coffee or tea without knowing that, beyond the immediate energy boost, they could be quietly protecting their brain. Now, a monumental study published in JAMA, the journal of the American Medical Association, confirms it with strong data: regular consumption of caffeinated coffee and tea is associated with a significant reduction in the risk of dementia and improved cognitive performance throughout life.

The research, led by the Harvard T.H. Chan School of Public Health and Brigham and Women's Hospital, represents the most extensive follow-up to date on this question: 43 years of observation and more than 130,000 participants who meticulously answered questionnaires about their eating habits every two to four years.

🧠 A growing problem: why this study is relevant now

Alzheimer's disease and other forms of dementia currently affect more than 6 million people in the United States, a number that is projected  to double to 13 million by 2050. With limited therapeutic options, considerable side effects in the available drugs, and the absence of a definitive cure, early prevention has become the most promising strategy to face this public health crisis.

In this context, diet and lifestyle emerge as modifiable factors of enormous potential. "What we eat and drink on a daily basis could have a cumulative impact on our brain health decades later," the researchers explain.

🔬 Here's how the study was conducted: 43 years of data in two flagship cohorts

The researchers analyzed data from two of the world's longest-running epidemiological studies:

Cohort	Participants	Profile	Follow-up period
Nurses' Health Study (NHS)	86,606 women	Nursing professionals, mean initial age 46.2 years	1980-2023
Health Professionals Follow-up Study (HPFS)	45,215 men	Health professionals, mean initial age 53.8 years	1986-2023

All participants were free of cancer, Parkinson's disease, and dementia at baseline. Beverage intake was assessed using validated food frequency questionnaires, administered every 2 to 4 years, which allowed changes in habits to be captured over time — a crucial methodological advantage over previous studies that only measured diet once.

During a median follow-up of 36.8 years, 11,033 incident cases of dementia were documented, identified through death records and medical diagnoses.

📊 Main results: caffeine makes a difference

Caffeinated coffee: 18% less risk

Participants who consumed the most caffeinated coffee — a median of 4.5 cups daily in women and 2.5 cups daily in men — performed markedly better on all indicators:

• Risk of dementia: 18% reduction  compared to those who consumed almost no coffee (141 vs. 330 cases per 100,000 person-years; HR = 0.82; 95% CI: 0.76-0.89)
• Subjective cognitive impairment: prevalence of 7.8% in frequent users vs. 9.5% in the lowest consumption group (15% reduction)
• Target cognitive performance (assessed only in the NHS female cohort): higher scores on the TICS telephone test (mean difference: 0.11 points; p=0.03) and positive trend in global cognition (p=0.06)

Caffeinated Tea: Similar Benefits with Fewer Cups

Caffeinated tea showed a comparable pattern of protection:

• Dementia risk: 14% reduction  in the tertile of highest consumption (HR = 0.86; 95% CI: 0.83-0.90)
• Subjective cognitive impairment: 14% reduction in prevalence
• Cognitive performance: mean difference of 0.16 points in ICTs (p=0.001)

Decaffeinated coffee: no protective effect

A particularly telling finding was that decaffeinated coffee did NOT show any significant association with reduced risk of dementia or improvements in cognitive function. This lack of benefit points directly to caffeine — and not to other compounds in coffee such as polyphenols — as the main neuroprotective agent in these beverages.

📈 The "perfect dose": nonlinear relationship and sweet spot

Dose-response analysis revealed a nonlinear pattern  of great clinical interest. The benefits do not increase indefinitely with each additional cup; There is a point of maximum benefit beyond which additional consumption does not bring advantages and could even be counterproductive:

Drink	Optimal daily intake	Observations
Caffeinated coffee	2-3 cups	Higher consumption does not offer additional benefits
Caffeinated tea	1-2 cups	Higher consumption does not improve results

This pattern has a plausible biological explanation. According to the researchers, "the absorption, transport, metabolism and storage of caffeine and other bioactive compounds have physiological limits". Specifically, liver enzymes responsible for caffeine metabolism — particularly CYP1A2 — can become saturated at high doses, creating a threshold effect.

In addition, excessive caffeine consumption could have counterproductive effects: altered sleep quality, increased anxiety, and other adverse effects that could neutralize or even reverse the neuroprotective benefits seen with moderate consumption.

🔍 How does caffeine protect the brain? Proposed mechanisms

Although the study is observational and cannot establish definitive causality, the researchers and neurologists consulted propose several biological mechanisms that would explain these findings:

1. Blocking adenosine receptors: Caffeine acts as an antagonist of adenosine A2A receptors in the brain, structures involved in inflammatory processes and in communication between neurons. "In laboratory studies and in animal models of Alzheimer's, blocking these receptors has been linked to a reduction in beta-amyloid protein accumulation and improved memory performance," explains Lynette Gogol, M.D., a neurologist specializing in lifestyle medicine.
2. Improved vascular health: Caffeine is associated with improved endothelial function and brain circulation, which may reduce the risk of vascular dementia — the second most common form of dementia after Alzheimer's.
3. Increased insulin sensitivity: Moderate caffeine consumption improves metabolic response, helping to prevent obesity, type 2 diabetes, and dyslipidemia — all established risk factors for cognitive decline.
4. Anti-inflammatory and antioxidant properties: Although the study suggests that caffeine is the main component, the polyphenols and other bioactive compounds present in both coffee and tea could also contribute by reducing oxidative stress and chronic neuroinflammation.

⚠️ Study Limitations: What It Does NOT Test

The authors and independent experts themselves point out important cautions that should be considered when interpreting these results:

• Reverse causality not ruled out: It is possible that early cognitive changes — even before clinical diagnosis — modify drinking patterns or affect the accuracy of dietary self-reports. People who are already experiencing incipient cognitive decline may be able to reduce their caffeine intake, creating an artificial association.
• Specific population: Both cohorts are composed of health professionals, a group with a higher educational and socioeconomic level than the general population, privileged access to medical care, and healthier lifestyle habits. This limits the generalizability of the findings to other demographic groups.
• Lack of granularity in the data: The questionnaires did not capture details such as the specific type of tea (green, black, oolong), the level of coffee roasting,  or brewing methods, variables that affect caffeine and antioxidant content and could influence the observed effects.
• Observational study: By design, research can only identify statistical associations, not causal relationships. It would take randomized clinical trials — difficult to conduct for decades — to establish definitive causation.

🩺 Clinical implications: what does it mean for you?

Despite these limitations, the magnitude and duration of the study give it considerable weight in the scientific literature. Dr. Nikhil Palekar, director of the Alzheimer's Disease Center of Excellence at Stony Brook Medicine, said: "The multi-decade extension of follow-up adds credibility to the findings.

For the general public, the message is clear but nuanced:

✅ If you already consume caffeinated coffee or tea and tolerate it well, you can confidently maintain a habit of 1-3 cups daily as part of a brain-healthy lifestyle.

❌ The study does NOT recommend that people who do not consume caffeine start doing so solely because of these findings. Caffeine can cause adverse effects in sensitive people: anxiety, insomnia, tachycardia, arrhythmias and dehydration. Always consult with your doctor before significantly modifying your intake.

⚠️ More is not better: Exceeding 3 cups of coffee or 2 cups of tea a day does not seem to provide additional cognitive benefits and could carry risks.

🔮 Next steps in the investigation

The Harvard team will continue to investigate this line. Priorities include:

• Elucidate the precise molecular mechanisms by which caffeine and other compounds in coffee and tea influence cognitive health.
• Analyze differences by type of tea (green vs. black) and coffee preparation method (filtered, espresso, French press).
• Exploring genetic interactions: Do people with variants in the CYP1A2 gene (which metabolize caffeine more slowly) get the same benefits?

📚 Study data sheet

Item	Detail
Original title	Coffee and Tea Intake, Dementia Risk, and Cognitive Function
Magazine	JAMA (Journal of the American Medical Association)
Publication	February 9, 2026 (online); Vol. 335, No. 11, pp. 961-974
DOI	10.1001/jama.2025.27259
Lead author	Yu Zhang, MBBS (Hospital Brigham and Women's)
Correspondence Author	Dong D. Wang, MD, ScD (dow471@mail.harvard.edu)
Funding	National Institutes of Health (NIH) of the USA
Conflict of interest	Dr. Frank Hu reports funding from the Analysis Group; Other authors without conflicts

📎 The full article is available at: JAMA Network

📬 Press Contact: Department of Communication, Harvard T.H. Chan School of Public Health

This article is for informational purposes only and is not a substitute for professional medical advice. Consult your neurologist or GP before making any changes to your diet or caffeine intake.

 

Close