Drinking just two or three cups of coffee a day is enough to reduce the risk of dementia by 18 percent and preserve cognitive function in both men and women, researchers said Monday.
And men and women who drink one or two cups of tea a day also had similar results, according to a new study of more than 131,000 people.
The key is caffeine, according to scientists at Mass General Brigham, the Massachusetts Institute of Technology and the Harvard TH Chan School of Public Health.
Previous research on caffeine has been mixed, with some studies showing beneficial effects of caffeinated coffee on the brain and others claiming that caffeine is harmful. But researchers say their findings suggest the chemical has brain-protective benefits.
“While our results are encouraging, it is important to remember that the effect size is small and that there are many important ways to protect cognitive function as we age,” Dr. Daniel Wang, an assistant professor at Harvard Medical School, explained in a statement. “Our study suggests that consumption of caffeinated coffee or tea may be one piece of that puzzle.”
A surprising difference
The study included data from 131,821 American participants collected over more than 40 years as part of the Nurses' Health Study and the Harvard Health Professionals Follow-up Study.
Participants underwent assessments of their diet, dementia, and cognitive status.
The researchers then compared and analyzed how their coffee and tea consumption, including decaffeinated beverages, may have affected each patient over the years.
Coffee is the most popular drink in the United States. According to the National Coffee Association, two-thirds of American adults drink coffee every day.
Overall, they found that caffeinated coffee drinkers had a lower prevalence of cognitive impairment than those who drank little or no caffeinated coffee.
People who drank the most coffee per day had the lowest incidence rate of dementia compared to people who drank the least: 141 top coffee drinkers developed the condition per 100,000 versus 330 people per 100,000, respectively.
The researchers found that caffeinated coffee drinkers also performed better on tests of cognitive function.
“Higher tea intake showed similar results, while decaffeinated coffee did not, suggesting that caffeine may be the active factor producing these neuroprotective results, although more research is needed to validate the factors and mechanisms responsible,” said General Mass Brigham.
More than 11,000 participants still developed dementia.
A ticking clock
More than seven million Americans live with dementia and that number is expected to nearly double by 2050, according to the Alzheimer's Association.
There is no cure for dementia, but there are ways to slow the progression of the disease. That's why early detection and prevention efforts are crucial, researchers say.
For example, a healthy diet and exercise are associated with reductions in the risk of dementia.
According to the Johns Hopkins Bloomberg School of Public Health, just 35 minutes of moderate to vigorous exercise per week was associated with a 41 percent lower risk of developing dementia over four years.
And the Mediterranean-adjacent MIND diet has been identified as effective in reducing the risk of dementia, say researchers at Columbia University.
Of course, one of the risk factors for dementia is genetic.
Fortunately, the new study showed that the benefits of coffee or caffeine were able to overcome that obstacle, said Yu Zhang, Ph.D. student at Harvard Chan School and research trainee at Mass General Brigham, he said.
“We also compared people with different genetic predispositions to developing dementia and obtained the same results, which means that coffee or caffeine is probably equally beneficial for people with high and low genetic risk of developing dementia,” Zhang said.
