2 to 3 cups of coffee a day may reduce the risk of dementia, study finds

If you think your daily espresso or tea makes your head smarter, you might be right, new research indicates.

A recent large study provided evidence of the cognitive benefits of coffee and tea — as long as they contain caffeine and are consumed in moderation: around two to three cups of coffee or one to two cups of tea per day.

People who maintained this drinking pattern for decades were less likely to develop dementia than those who drank little or no caffeine, researchers found. In total, 131,821 participants were followed for up to 43 years.

“It’s a very large, rigorous, long-term study of men and women that shows that drinking two or three cups of coffee a day is associated with a lower risk of dementia,” said Aladdin Shadyab, an associate professor of public health and medicine at the University of California, San Diego, who was not involved in the research.

The results, published this Monday in JAMA, do not prove that caffeine is the direct cause of these positive effects — it is possible that other factors associated with coffee and tea consumption helped protect the brain. But independent experts highlight that the study controlled a series of variables, such as pre-existing diseases, medication use, diet, education, socioeconomic status, family history of dementia, body mass index, smoking and mental health problems.

The association between caffeine and lower risk of dementia appeared even among people with a genetic risk for Alzheimer’s or other types of dementia. The study, funded by the US National Institutes of Health, did not differentiate between subtypes of the disease.

Some previous work did not find clear cognitive benefits linked to caffeine, but generally had limitations: shorter follow-up or assessment of the diet at just one point in time, for example. The new study adds to a growing body of evidence “that suggests that caffeinated coffee may reduce the risk of chronic diseases associated with aging,” says Shadyab.

The researchers followed participants from two classic studies of healthcare professionals: women from the Nurses’ Health Study and men from the Health Professionals Follow-up Study. Mostly in their 40s or 50s at the start, they responded, over the years, to a sequence of questionnaires about diet, health and lifestyle. During this period, 11,033 participants developed dementia, documented on death certificates or medical diagnoses.

Compared to those who consumed virtually no caffeine, those who drank between one and five cups of caffeinated coffee per day had about a 20% lower risk of dementia. Among those who drank at least one cup of caffeinated tea a day, the reduction was approximately 15%.

Above something like 2 and a half cups of coffee per day, however, the benefit seemed to stabilize, possibly because the body is unable to take advantage of the bioactive compounds present in coffee and tea beyond that, explained the study’s senior author, Daniel Wang, an epidemiologist specializing in neurodegenerative diseases at the Mass General Brigham health system.

Wang, who says he drinks about three cups of coffee and three cups of green tea every day, said research has found no clear negative effects linked to higher amounts of caffeine. Even so, other studies suggest that exceeding the range considered moderate can harm health by disrupting sleep or worsening anxiety, recalls epidemiologist Fang Fang Zhang, from the school of nutrition at Tufts University, who was not involved in the work.

In a 2025 study that linked caffeine consumption to lower mortality, Zhang says that his team also observed that “there is no additional gain when going beyond three cups.” According to her, adding more than a little milk or sugar to the drink negated the benefit of caffeine in terms of mortality. The dementia study did not track milk or sugar use.

In addition to dementia, the new work analyzed reports of subjective cognitive decline — when a person themselves feels that their memory and thinking are getting worse, often an early sign on the path toward dementia. Those who consumed more caffeine reported this type of complaint less.

Around 17,000 participants, all women over 70, also took periodic cognitive tests. Those who drank more caffeinated beverages performed slightly better for their age, which suggests that cognitive decline was, on average, about seven months slower, Wang says.

Scientists believe that caffeine may protect the brain by concentrating substances that reduce neuroinflammation or improve blood vessel function. There is also evidence that it increases insulin sensitivity, helping to prevent diabetes — a major risk factor for dementia.

For those who don’t consume caffeine, Shadyab says that the results “don’t necessarily mean that we should encourage everyone to start drinking coffee, but they bring some relief to those who already do: it may help reduce the risk of dementia.”

Zhang believes that those who do not drink caffeinated coffee or tea can “experiment”, starting with small amounts, especially if they are more sensitive to the stimulating effect.

The association between caffeine and lower risk of dementia was strongest among people under 75. Wang recalls that cognitive impairment develops over decades: “If you can change health habits earlier, before middle age, the gain tends to be greater.”

Because participants are healthcare professionals, they may not perfectly represent the general population. But Zhang notes that the heaviest caffeine drinkers were also more likely to smoke and drink alcohol, indicating that they weren’t necessarily much healthier than the average American.

The researchers were unable to completely rule out all possible influences on the results. An example cited in the article: wouldn’t some people be drinking decaffeinated coffee for health reasons that would increase the risk of dementia — “and not because of a direct effect of the drink”?

They also failed to answer that question that many coffee and tea lovers would like to see answered: which is better for the brain — a Darjeeling or a matcha? A Sumatra or a Colombian? A $6 Americano or that free, cardboard-tasting coffee from the office machine?