People who drank the most coffee were 18 percent less likely to develop dementia than those who rarely if ever drank coffee, according to the study. Similarly, individuals who drank the most tea were 14 percent less likely to develop dementia than those who rarely or never had tea.
Decaf coffee, however, was not tied to these benefits. The study did not collect data on decaf tea.
It may be that caffeine protects the brain, but only to a certain point, says Yu Chen, PhD, MPH, a professor of epidemiology and population health and New York University and NYU Langone Health, who wasn’t involved in the new study.
How Much Coffee or Tea Provided Maximum Benefit?
Researchers followed more than 130,000 adults for around four decades starting when they were in their mid-forties to mid-fifties. Every two to four years, participants completed dietary questionnaires that asked how many 8-ounce cups of coffee, decaf, and tea, they drank each day.
None of the participants had dementia when they joined the study. By the end, however, over 11,000 people had developed this condition, according to findings published in the Journal of the American Medical Association.
After evaluating these outcomes with participants’ beverage habits, researchers found that the cognitive benefits of coffee were most pronounced for people who consumed 2 to 3 cups a day. Brain health benefits of tea peaked at about 1 to 2 cups daily.
When people had more coffee or tea than this, they didn’t see much additional benefit in terms of promoting brain health.
The study didn’t look at how subjects prepared their beverages, and this might make a difference when it comes to the overall health impact, says Glen Finney, MD, a neurology professor at Geisinger College of Health Sciences and director of the Geisinger Memory and Cognition Program in Scranton, Pennsylvania.
“I think modest consumption of caffeinated coffee or tea may be of benefit for brain health,” says Dr. Finney, who wasn’t involved in the new study. “But I would caution to drink it earlier in the day rather than at night, and to avoid adding lots of sweeteners or fats like heavy cream, as they aren’t healthy.”
How Coffee and Tea Might Protect the Brain
While the study wasn’t designed to prove whether or how coffee or tea might directly prevent dementia, it’s possible that plant compounds like polyphenols in these beverages might play a role, says senior study author Daniel Wang, MD, ScD, 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 in Boston.
“These compounds can reduce inflammation and oxidative stress and support blood vessel function and metabolic health,” Dr. Wang says.
Oxidative stress, which develops when the body has low levels of antioxidants and high levels of unstable molecules known as free radicals, can lead to cell damage. Over many decades, inflammation and oxidative stress can accelerate brain aging, Wang says.
Caffeine may interfere with processes in the brain that allow the buildup of harmful proteins like amyloid beta that are linked to Alzheimer’s disease, a common form of dementia, Dr. Chen says.
Caffeine can also curb inflammation in the brain, and support plasticity, or the brain’s ability to respond and adapt to new information and situations, Chen adds.
Study Has Some Limitations
One limitation of the study is that researchers identified dementia cases based on death records and diagnoses recorded in medical records when available. This makes it possible that some cases were misclassified or went undetected, and it also didn’t allow researchers to separately distinguish cases of Alzheimer’s disease.
Another drawback is that researchers lacked data on what type of tea people drank, making it impossible to determine the impact of caffeinated forms like black tea as opposed to herbal blends or other uncaffeinated options.
It’s also possible that people with better cognition are more apt to choose to drink caffeinated coffee and tea, as opposed to these beverages causing better brain health, says Andrew Budson, MD, a neurology professor at Boston University and coauthor of Seven Steps to Managing Your Aging Memory.
“It is certainly true that people who work, who need to get up for a job or other responsibilities, and people who need to perform well are more likely to drink caffeinated coffee and tea,” says Dr. Budson, who wasn’t involved in the new study. “So that is another possible explanation.”
The Bottom Line on Drinking Coffee and Tea for Brain Health
“I wouldn’t tell someone to start drinking coffee just as a dementia prevention treatment,” says lead study author Yu Zhang, MBBS, a PhD candidate at the Harvard T.H. Chan School of Public Health and Mass General Brigham in Boston.
“But for people who already drink coffee or tea, our findings suggest that moderate intake is compatible with brain health and is associated with lower dementia risk,” Zhang says.
Beyond this, people who’ve previously been told by their doctor to avoid coffee or tea for health reasons might want to ask at their next checkup if this is still true, Budson says. “My recommendation would be for them to speak with their provider about what makes sense for their overall health, now that we have some new reasons to drink caffeinated coffee and tea,” Budson says.
At the same time, coffee and tea drinkers need to keep in mind that this isn’t the main way to prevent dementia, Chen says. “Overall, dementia prevention still relies primarily on healthy lifestyle factors such as regular exercise, vascular risk control, a balanced diet, adequate sleep, and cognitive engagement,” Chen says.