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For millions of Americans who start the day with a cup of coffee or tea, new research offers another possible reason to enjoy the habit. A large Harvard-led study suggests that moderate consumption of caffeinated coffee or tea is associated with a lower risk of developing dementia and may help preserve cognitive function as people age. 

The study, published in the Journal of the American Medical Association (JAMA), analyzed data from 131,821 participants in the long-running Nurses’ Health Study and Health Professionals Follow-Up Study. Researchers tracked participants for as long as 43 years, examining their beverage consumption alongside dementia diagnoses and measures of cognitive performance. 

The researchers found that people who drank two to three cups of caffeinated coffee per day or one to two cups of caffeinated tea daily experienced the strongest association with better brain health. 

Compared with people who consumed little or no caffeinated coffee, moderate coffee drinkers had roughly an 18% lower risk of developing dementia. Similar benefits were observed among tea drinkers.

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Additional findings

The study also found that participants who regularly consumed caffeinated coffee or tea reported less subjective cognitive decline and performed modestly better on objective cognitive tests over time. 

One notable finding was what researchers did not see: decaffeinated coffee was not associated with a reduced risk of dementia or improved cognitive performance, suggesting caffeine or other compounds present in caffeinated beverages may play an important role. 

Lead author Yu Zhang and senior author Daniel Wang, a Harvard T.H. Chan School of Public Health researcher and Mass General Brigham physician-scientist, said the findings represent some of the strongest evidence to date linking habitual coffee and tea consumption with cognitive health. However, they emphasized that the study cannot establish cause and effect because it was observational.

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Several contributing factors

Researchers believe several biological mechanisms could explain the association. Coffee and tea contain caffeine and polyphenols, compounds that may reduce inflammation and oxidative stress, improve vascular health, and support healthy metabolism — all factors that have been linked to brain health. 

The investigators also found that the apparent benefit leveled off at moderate intake, with higher consumption offering little additional protection. 

Even with the encouraging findings, the researchers said coffee and tea should not be viewed as standalone strategies for preventing dementia. They stressed that regular physical activity, a balanced diet, quality sleep, and management of cardiovascular risk factors remain among the most important ways to support long-term cognitive health.