Coffee is everywhere, and so are the debates around it. Does it stunt growth? Ruin sleep? Boost performance? There’s no shortage of caffeine discourse. But today’s topic is one worth paying attention to: a major new JAMA study examining whether long-term caffeine consumption is linked to dementia risk.
TLDR: coffee drinkers have reason to be encouraged.
The Study
In this line of work, skepticism comes with the territory. Scientific papers often present their most exciting findings front and center, and abstracts don’t always capture the full nuance of the evidence. That’s why we make a habit of reading beyond the headlines.
Every so often, though, a study arrives that genuinely lives up to the hype. This is one of them.
The study drew on two large US cohorts over its 43-year data collection period: the Nurses’ Health Study (86,606 women, 1980–2023) and the Health Professionals Follow-up Study (45,215 men, 1986–2023). All participants were free of cancer, Parkinson’s disease, and dementia at the start. Researchers tracked intake of caffeinated coffee, decaffeinated coffee, and tea, then followed three outcomes: incident dementia (confirmed through death records and physician diagnoses), self-reported cognitive decline, and objective cognitive performance on telephone-based neuropsychological tests.
What They Found
The headline finding: higher caffeinated coffee intake was associated with substantially lower dementia risk. Dementia incidence dropped from 330 per 100,000 person-years in the lowest intake group down to 141 per 100,000 in the highest. Tea drinkers saw similar benefits, with the heaviest tea consumers showing a 14% lower hazard of dementia compared to the lightest. Higher intake of both beverages was also linked to lower rates of self-reported cognitive decline and, in the women’s cohort, modestly better scores on objective cognitive tests.
Importantly, more was not always better. The strongest protective associations appeared at roughly two to three cups of caffeinated coffee per day (about 300 mg of caffeine). Beyond that seems to offer little added benefit. Just make sure those cups are front-loaded: emerging evidence suggests keeping your last coffee at least 8–9 hours before bedtime if you value your sleep.
One of the more intriguing findings involved decaffeinated coffee. Not only did decaf fail to show a protective association, but it was also linked to a small increase in subjective cognitive decline. The authors are appropriately cautious in interpreting this result. Still, they suggest that caffeine itself may be driving at least part of the observed benefit. Biologically, that idea is plausible. Caffeine has been shown to reduce oxidative stress and neuroinflammation, improve insulin sensitivity and vascular function, and may even influence Alzheimer’s-related amyloid and tau pathways.
The Caveats
As impressive as these findings are, this remains an observational study. Thus, we must harken back to the first rule taught in undergrad stats classes: association does not equal causation.
One important concern arising from this paper is reverse causation: people in the earliest stages of cognitive decline may naturally reduce their coffee consumption, making lighter coffee drinkers appear at greater risk. To address this, the researchers performed time-lagged analyses and excluded participants with major chronic diseases at baseline. The results remained largely unchanged. Even so, reverse causation cannot be completely ruled out.
Residual confounding is another limitation. Compared with lighter coffee drinkers, heavier coffee drinkers in this cohort also tended to be younger, drink more alcohol, and smoke more. While the analyses adjusted for these factors, observational studies can never account for every possible difference between groups.
The Bottom Line
Does this study prove that coffee prevents dementia? No. But with 43 years of follow-up and over 130,000 participants, it is among the strongest epidemiological evidence to date that regular, moderate caffeinated coffee or tea consumption is associated with meaningfully lower dementia risk. For once, the evidence is squarely on the side of something most of us are already doing anyway.
Sophie Tseng Pellar is a Masters Student in the Surgical and Interventional Sciences program at McGill. Her research interests include exercise physiology, biomechanics and sports nutrition.
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