Your daily coffee may be protecting your brain, 43-year study finds

"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," said senior author Daniel Wang, MD, ScD, associate scientist with the Channing Division of Network Medicine in the Mass General Brigham Department of Medicine and assistant professor at Harvard Medical School. Wang is also an assistant professor in the Department of Nutrition at Harvard Chan School and an associate member at the Broad Institute. "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."

Why Prevention Matters for Dementia

Preventing dementia early is especially important because current treatments are limited and generally provide only modest benefits after symptoms begin. As a result, scientists are increasingly focusing on lifestyle factors, including diet, that may influence the development of cognitive decline.

Coffee and tea contain compounds such as polyphenols and caffeine, which are thought to support brain health. These substances may help reduce inflammation and limit cellular damage, both of which are linked to cognitive decline. However, previous research on coffee and dementia has produced mixed results, often due to shorter study periods or limited data on long-term consumption patterns and different types of beverages.

Long-Term Data Offers Clearer Insights

The NHS and HPFS datasets helped address these gaps. Participants were tracked for up to 43 years, with repeated evaluations of diet, dementia diagnoses, subjective cognitive concerns, and objective cognitive performance. Researchers analyzed how consumption of caffeinated coffee, tea, and decaffeinated coffee related to long-term brain health outcomes.

Among the more than 130,000 participants, 11,033 developed dementia over the course of the study. Individuals who consumed higher amounts of caffeinated coffee had an 18% lower risk of developing dementia compared with those who rarely or never drank it. They also reported lower rates of subjective cognitive decline (7.8% versus 9.5%) and performed better on certain objective cognitive tests.

Caffeine May Play a Key Role

Similar patterns were observed among tea drinkers, while decaffeinated coffee did not show the same associations. This suggests that caffeine may be an important factor behind the observed brain-related benefits, although more research is needed to confirm the underlying mechanisms.

The strongest effects were seen in participants who drank 2-3 cups of caffeinated coffee or 1-2 cups of tea per day. Higher levels of caffeine intake did not appear to cause harm. Instead, they showed comparable benefits to the moderate intake range highlighted in the study.

"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," said lead author Yu Zhang, MBBS, MS, PhD student at Harvard Chan School and a research trainee at Mass General Brigham.

Study Authors and Funding

In addition to Wang and Zhang, Mass General Brigham contributors included Yuxi Liu, Yanping Li, Yuhan Li, Jae H. Kang, A. Heather Eliassen, Molin Wang, Eric B. Rimm, Frank B. Hu, and Meir J. Stampfer. Additional authors were Walter C. Willett and Xiao Gu.

The research was supported by National Institutes of Health grants UM1 CA186107, U01 HL145386, U01 CA167552, R01 HL60712, P30 DK46200, R00 DK119412, R01 AG077489, RF1 AG083764, and R01 NR019992. The funding organizations had no involvement in the study design, data collection, analysis, manuscript preparation, or the decision to publish.