Case: A 42-year-old emergency physician working alternating day and night shifts drinks several cups of coffee each day and jokes that caffeine should probably be listed as an adjunct faculty member in the department. After hearing about a large new study linking coffee and tea intake with lower dementia risk, she asks a simple question: Is her daily caffeine habit hurting her brain or helping it?

Background: Emergency physicians do not need a pathophysiology lecture on caffeine; they need a fresh cup and a functioning badge scanner. Coffee is practically a staffing model in emergency medicine, whereas tea is the civilized cousin that usually appears midway through a run of night shifts when the tremor from cup number four becomes clinically significant. For decades, caffeine has been the unofficial performance-enhancing substance of emergency medicine.

Coffee’s origin story reads like a caffeinated case report from antiquity. Legend traces it back to Ethiopia, where a goat herder reportedly noticed his animals becoming unusually energetic after eating berries from a particular shrub. From there, coffee spread through the Arabian Peninsula and eventually into Europe by the 17th century, where coffeehouses became centers for conversation, politics, scholarship, and probably the earliest forms of aggressive peer review. Coffee was alternately praised as a miracle tonic and criticized as a dangerous stimulant.

The biologic rationale for coffee and tea affecting cognitive health is at least plausible. Both beverages contain caffeine and a variety of bioactive compounds, including polyphenols and antioxidants, which may influence oxidative stress, neuroinflammation, vascular function, insulin sensitivity, and other pathways potentially involved in cognitive decline and dementia. Experimental studies have suggested possible neuroprotective effects, but human observational studies have produced mixed results over the years.

Clinical Question: Does the amount of coffee and tea emergency physicians consume to survive night shifts merely keep us functional during residency and overnight staffing shortages, or could it influence long-term cognitive health and dementia risk?

Reference: Zhang Y, Liu Y, Li Y, et al. Coffee and Tea Intake, Dementia Risk, and Cognitive Function. JAMA. 2026; 335(11):961-974. doi: 10.1001/jama.2025.27259.

• Population: Nurses’ Health Study (NHS) and Health Professionals Follow-up Study (HPFS).
  • Excluded: People with cancer, Parkinson’s disease, or dementia at baseline; those with implausible total energy intake; and those missing caffeinated beverage intake data. 
• Exposure: Long-term intake of caffeinated coffee, decaffeinated coffee, and tea, assessed every two to four years with validated food frequency questionnaires (FFQs). 
• Comparison: Lower intake categories
• Outcomes:
  • Primary outcome: Incident dementia
  • Secondary outcomes: Subjective cognitive decline and objective cognitive function; objective testing was assessed only in the NHS cohort, including a telephone interview for cognitive status (TICS) and composite cognitive measures. 
• Type of Study: Prospective observational cohort study.

Authors’ Conclusions: “Greater consumption of caffeinated coffee and tea was associated with lower risk of dementia and modestly better cognitive function.” 

Results: The two cohorts included 131,821 middle-aged US health professionals, of whom 66 percent were women. Median follow-up at 37 years. Higher coffee consumers tended to be younger, drink more alcohol, smoke more, and consume more total energy. 

Key Result: Health professionals who drank more caffeinated coffee appeared less likely to develop dementia.

• Primary Outcome: Compared with participants in the lowest quartile of caffeinated coffee consumption, those in the highest quartile had a significantly lower risk of incident dementia (hazard ratio (HR) 0.82; 95 percent confidence interval (CI) 0.76 to 0.89). Tea consumption showed a similar association, whereas decaffeinated coffee did not.
  

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• Secondary Outcomes:

Talk Nerdy

1. Residual Confounding and Healthy User Bias: This is the biggest limitation of any observational nutrition study. Even after multivariable adjustment, people who drink more coffee or tea may differ systematically from those who do not in ways that influence cognitive outcomes. These differences may include sleep habits, exercise, education, socioeconomic status, health-seeking behavior, medication use, and overall lifestyle. The authors adjusted for many of these variables, but residual confounding is almost certainly still present. In other words, coffee drinkers may simply differ from non-coffee drinkers in ways that are difficult to fully measure or control.

2. Reverse Causation and Time-Varying Exposure: Early or subclinical cognitive decline could itself change caffeine habits long before a formal dementia diagnosis occurs. People with cognitive impairment may reduce coffee intake due to sleep disturbance, palpitations, gastrointestinal symptoms, or caregiver influence, making coffee appear protective when the disease process alters exposure. This issue is compounded by the fact that coffee and tea consumption likely changed substantially over the 30- to 40-year follow-up period. Even with repeated FFQs, long-term caffeine exposure is difficult to measure accurately over decades.

3. Imperfect Measurement of Exposure and Outcomes: Although repeated validated FFQs are better than a single baseline dietary survey, they still cannot fully capture brew strength, serving size, preparation methods, or changes between caffeinated and decaffeinated products. Similarly, dementia ascertainment relied partly on death records and physician diagnoses rather than standardized in-person cognitive assessments for all participants. These limitations introduce the possibility of exposure misclassification and outcome misclassification, both of which can distort observed associations in longitudinal observational studies.

Bottom Line: Good news for emergency physicians: Your moderate coffee habit may be associated with a lower risk of dementia.

Case Resolution: The emergency physician does not need to panic that their caffeine intake is hurting their brain. It appears that moderate intake of caffeinated coffee or tea is associated with lower dementia risk and slightly better cognitive outcomes, but the observational design cannot establish causation. For emergency physicians who already drink coffee to survive circadian disruption and overnight shifts, this paper suggests their habit is unlikely to harm long-term cognitive health and may even confer some benefit. However, there is no evidence here to recommend escalating caffeine intake beyond moderation, particularly if it worsens anxiety, insomnia, palpitations, reflux, or blood pressure.

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.

Thank you to Dr. Manrique Umana, an emergency physician working in Costa Rica, for his help with this review.

Dr. Milne

Dr. Milne is a staff physician at the Strathroy Middlesex General Hospital in Strathroy, Ontario, Canada, and is an associate professor in the Department of Medicine (Division of Emergency Medicine) and Department of Family Medicine at the Schulich School of Medicine and Dentistry.