A massive decades-long study suggests that 2–3 cups of coffee or 1–2 cups of tea a day are linked with lower dementia risk and better cognitive function. Researchers say caffeine may play a key role, but it is only one piece of a broader brain-health puzzle.
A daily cup of coffee or tea might do more than help you wake up. It could also be linked to a lower risk of dementia and a slower decline in thinking skills over time, according to a major new study.
Researchers from Mass General Brigham, the Harvard T.H. Chan School of Public Health and the Broad Institute analyzed data from 131,821 adults who were followed for up to 43 years. They found that people who regularly drank moderate amounts of caffeinated coffee or tea were less likely to develop dementia and tended to perform better on cognitive tests.
The findings, published in the journal JAMA, draw on two of the most influential long-running health studies in the world: the Nurses’ Health Study and the Health Professionals Follow-Up Study. Participants repeatedly reported what they ate and drank, including coffee and tea, and completed assessments of memory, thinking and dementia diagnoses over decades.
The team wanted to know whether a simple, everyday habit could make a measurable difference for brain health over the long term, according to senior author Daniel Wang, an associate scientist with the Channing Division of Network Medicine in the Mass General Brigham Department of Medicine and assistant professor at Harvard Medical School.
“When searching for possible dementia prevention tools, we thought something as prevalent as coffee may be a promising dietary intervention—and our unique access to high quality data through studies that has been going on for more than 40 years allowed us to follow through on that idea,” Wang, who is also an assistant professor in the Department of Nutrition at Harvard Chan School and an associate member at the Broad Institute, said in a news release.
Dementia, which includes Alzheimer’s disease and related disorders, affects millions of older adults worldwide. Because current treatments are limited and often offer only modest benefit once symptoms appear, scientists are increasingly focused on prevention and on lifestyle factors that might help protect the brain.
In this study, more than 11,000 of the participants developed dementia over the follow-up period. When the researchers compared people based on how much caffeinated coffee they drank, they found that those with the highest intake had an 18 percent lower risk of dementia than those who reported little or no caffeinated coffee.
The pattern was similar for tea. People who drank more tea also tended to have lower dementia risk and better cognitive outcomes. The benefits were strongest among those who consumed about 2–3 cups of caffeinated coffee a day or 1–2 cups of tea a day.
Caffeinated coffee drinkers were also less likely to report subjective cognitive decline, meaning they were less likely to feel that their memory or thinking was getting worse. About 7.8% of regular caffeinated coffee drinkers reported this kind of decline, compared with 9.5% of people who rarely or never drank caffeinated coffee. On objective tests of overall cognitive function, coffee drinkers also tended to score higher.
By contrast, decaffeinated coffee did not show the same protective pattern. That difference suggests that caffeine itself may be a key factor, though coffee and tea also contain other bioactive compounds, such as polyphenols, that may help reduce inflammation and protect brain cells. The authors note that more research is needed to pinpoint which components and biological pathways are responsible.
Lead author Yu Zhang, a doctoral student at Harvard Chan School and research trainee at Mass General Brigham, noted the results held up even when they looked at people’s inherited risk.
“We also compared people with different genetic predispositions to developing dementia and saw the same results—meaning coffee or caffeine is likely equally beneficial for people with high and low genetic risk of developing dementia,” Zhang said in the news release.
That finding is especially important because many people worry that a strong family history of dementia means there is little they can do. The study suggests that everyday choices, including what you drink, may matter regardless of genetic background.
The research also addresses some of the confusion from earlier studies on coffee, tea and brain health. Previous work often had shorter follow-up periods, less detailed information on long-term drinking habits, or focused only on diagnosed dementia rather than the full spectrum from early memory complaints to clinical disease. By tracking people over several decades and repeatedly measuring both diet and cognition, the new study offers a more complete picture of how these beverages relate to brain aging.
Interestingly, the researchers did not see evidence that higher caffeine intake was harmful for brain health within the ranges they studied. Even people who drank more than the “optimal” amount of coffee or tea generally showed similar neuroprotective patterns rather than worse outcomes. Still, the authors emphasize that caffeine can have other side effects, such as sleep problems or heart palpitations, and that individuals should consider their overall health and talk with their clinicians.
Wang stressed that coffee and tea are not magic bullets and should be viewed as part of a broader brain-healthy lifestyle that includes regular physical activity, a balanced diet, managing blood pressure and staying socially and mentally engaged.
“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,” Wang added.
Because this was an observational study, it cannot prove that coffee or tea directly prevent dementia. It is possible that people who drink these beverages regularly also have other habits that support brain health. However, the researchers adjusted for many lifestyle and health factors in their analyses, and the consistent patterns across different measures and risk groups strengthen the case that caffeine-containing drinks may play a meaningful role.
Next steps for the field include clinical trials and mechanistic studies to understand exactly how caffeine and other compounds in coffee and tea might protect the brain. Scientists are also interested in whether timing of intake, such as drinking coffee earlier versus later in the day, or pairing these beverages with certain diets, might influence their effects.
For now, the study offers a hopeful message for students, professionals and older adults alike: that familiar mug on your desk or kitchen table might be doing more than helping you power through the day. In moderation, it could be one small, enjoyable way to support your brain as you age.
Source: Mass General Brigham