A study of over 130,000 people has found that drinking two to three cups of caffeinated coffee a day — or one to two cups of tea — is associated with an 18% lower risk of developing dementia compared to drinking little or none.
The research, published in JAMA, analyzed four decades of health data from the Nurses' Health Study and Health Professionals Follow-Up Study, two of the longest-running cohort studies in the US. Investigators from Mass General Brigham, Harvard T.H. Chan School of Public Health, and the Broad Institute tracked participants over time, watching for cognitive decline and dementia diagnoses.
"When searching for possible dementia prevention tools, we thought something as prevalent as coffee may be a promising dietary intervention," said Daniel Wang, an associate scientist at Mass General Brigham and assistant professor at Harvard Medical School who led the research. "Our unique access to high-quality data through studies that have been going on for more than 40 years allowed us to follow through on that idea."
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Start Your News DetoxThe findings are notable because they're based on such a large, long-term dataset. People who drank the most caffeinated coffee also reported fewer instances of subjective cognitive decline — that early-warning sense that your memory or thinking isn't quite as sharp as it used to be. About 7.8% of regular coffee drinkers reported this, compared to 9.5% of those who drank little or no coffee.
Tea showed similar protective effects. Decaffeinated coffee, however, did not — suggesting caffeine itself plays a role, though it's likely not the whole story. The researchers suspect bioactive compounds in coffee and tea, particularly polyphenols, may reduce inflammation and cellular damage in the brain. The benefits held up across people with both high and low genetic risk for dementia, suggesting the effect isn't limited to a particular group.
Wang is careful to keep expectations grounded. "While our results are encouraging, it's important to remember that the effect size is small and there are lots of important ways to protect cognitive function as we age. Our study suggests that caffeinated coffee or tea consumption can be one piece of that puzzle." Exercise, social connection, cognitive engagement, and sleep remain foundational to brain health — coffee is more like a bonus than a solution.
The research doesn't prove that coffee prevents dementia, only that the two are associated. But the consistency of the finding across such a large group, and over such a long period, makes it one of the more credible links between a everyday habit and cognitive protection.
