Two to three cups of coffee a day may help protect against dementia, but more caffeine does not improve—and may reduce—those benefits.
Drinking a few cups of coffee each day could do more than boost your energy. Research suggests it may also lower your chances of developing dementia, although increasing your intake beyond that range does not appear to offer additional protection.
The findings come from a large, long-running study that followed 131,821 American nurses and healthcare professionals for as long as 43 years, beginning when participants were in their early 40s. Over the course of the study, 11,033 individuals, about 8%, were diagnosed with dementia. Those who regularly consumed moderate amounts of caffeinated coffee or tea were less likely to develop the condition compared with those who drank little or none.
The benefit was most noticeable among people aged 75 and under. In this group, consuming around 250mg-300mg of caffeine per day, roughly equivalent to two or three cups of coffee, was associated with a 35% lower risk of dementia. Increasing caffeine intake beyond this level did not lead to further reductions in risk, suggesting there is a threshold where the benefit levels off.
At the start of the study, women reported drinking an average of about four and a half cups of coffee or tea daily, while men reported closer to two and a half cups. People who consumed higher amounts of caffeinated coffee were generally younger, but they also tended to drink more alcohol, smoke more, and take in more calories. Each of these factors has been linked to a higher risk of dementia, which makes it harder to isolate the effects of caffeine alone.
Interestingly, people who drank more decaffeinated coffee showed faster memory decline. Researchers believe this is probably because people switched to decaf after developing sleep problems, raised blood pressure, or heart rhythm disturbances – all of which are themselves linked to cognitive decline and dementia.
Why caffeine might protect the brain
There are sound biological reasons why caffeine could help keep our brains healthy. It works by blocking adenosine, a chemical that dampens the activity of brain messengers like dopamine and acetylcholine. These brain messengers (or neurotransmitters) can become less active as we age and in conditions such as Alzheimer’s disease, so caffeine’s stimulating effect may help counteract this decline.
Caffeine also appears to work through other mechanisms, including reducing inflammation and helping regulate blood sugar metabolism. People who did not have dementia (yet?) but drank more than two cups of coffee daily throughout their lives had lower levels of the toxic amyloid plaques, abundantly found in people’s brains who have Alzheimer’s disease.
Coffee and tea also contain many other beneficial compounds with antioxidant and blood vessel benefits which can all protect the aging brain.
Tea, dose limits, and diminishing returns
The American study found that only one to two cups of tea were linked to the best protection against dementia, which may reflect the fact that people in the US drink less tea than coffee overall. Green tea wasn’t examined separately, although most studies suggest it also protects against dementia.
Why does more caffeine stop being helpful? The researchers suggest it may be down to how our bodies break down coffee. Very high doses can also disrupt sleep and increase anxiety, which undermines any brain benefits.
A principle established back in 1908, known as the Yerkes-Dodson law, shows that when we become too stimulated – whether from anxiety or too much coffee – our mental performance starts to decline.
Evidence across studies supports moderation
The findings from professional healthcare workers may not apply to everyone. But when researchers combined results from 38 other studies, they found similar results: caffeine drinkers had a 6%-16% lower dementia risk than non-drinkers, with one to three cups of coffee being optimal. Good news for tea lovers – in this broader analysis, drinking more tea was linked to greater protection.
Moderate caffeine intake doesn’t increase long-term blood pressure risk and may even reduce cardiovascular disease risk, which shares many risk factors with dementia. However, people with very high blood pressure are advised to limit themselves to perhaps one cup a day.
It’s worth noting that using “cups” as a measure doesn’t account for how much caffeine these actually contain. Fresh beans brewed at home contain different amounts of caffeine and can affect cholesterol levels differently than instant coffee, for instance.
But you don’t need much to feel a benefit. Even low doses of 40mg-60mg can improve alertness and mood in middle-aged people who normally did not drink (much) caffeine. More is not always better.
Reference: “Coffee and Tea Intake, Dementia Risk, and Cognitive Function” by Yu Zhang, Yuxi Liu, Yanping Li, Yuhan Li, Xiao Gu, Jae H. Kang, A. Heather Eliassen, Molin Wang, Eric B. Rimm, Walter C. Willett, Frank B. Hu, Meir J. Stampfer and Dong D. Wang, 9 February 2026, JAMA.
DOI: 10.1001/jama.2025.27259
Adapted from an article originally published in The Conversation.
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