A couple of cups of coffee or tea each day could be linked to a lower risk of dementia and slightly better cognitive performance, according to a major new U.S. study published in the Journal of the American Medical Association.
Researchers who tracked the health records of more than 130,000 people over several decades found that those who regularly consumed moderate amounts of caffeinated coffee or tea were less likely to develop dementia than those who avoided the drinks.
The analysis showed that people who drank two to three cups of caffeinated coffee daily, or one to two cups of caffeinated tea, had a 15% to 20% lower risk of dementia over a 40-year period compared with non-drinkers.
Participants who consumed caffeinated coffee also reported slightly less cognitive decline than those who opted for decaffeinated versions and performed better on some objective tests of brain function. No similar link was found between decaf coffee and dementia risk.
“Our study alone can’t prove causality, but to our knowledge, it is the best evidence to date looking at coffee and tea intake and cognitive health,” said lead author Yu Zhang, a nutritional epidemiologist at Harvard University. Zhang noted that the findings align with “plausible biology.”
Coffee and tea contain caffeine as well as polyphenols — plant-based compounds that may help protect against brain ageing. Scientists believe these substances could support vascular health, reduce inflammation and limit oxidative stress, a process in which harmful molecules known as free radicals damage cells and tissues.
The drinks may also influence metabolic health. Caffeine has been associated with lower rates of type 2 diabetes, a known risk factor for dementia.
The study drew on data from 131,821 volunteers enrolled in two long-running U.S. research efforts: the Nurses’ Health Study and the Health Professionals Follow-up Study. Participants underwent repeated assessments of diet, dementia diagnoses, self-reported cognitive decline and performance on cognitive tests over as many as 43 years.
Overall, the highest caffeinated coffee consumers had an 18% lower risk of dementia than those who drank little or none, with similar results observed for tea. Researchers said the protective effect appeared to plateau at moderate levels — more was not necessarily better.
Experts cautioned, however, that observational research cannot prove that caffeine directly prevents dementia. People who drink coffee or tea may differ in other ways, such as sleep habits or lifestyle factors, that influence cognitive health.
Naveed Sattar, a professor of cardiometabolic medicine at the University of Glasgow, said caffeine can have both positive and negative effects, including raising blood pressure in some individuals — itself a major dementia risk factor.
Researchers estimate that about half of dementia cases worldwide could be prevented or delayed through healthier habits such as reducing smoking, limiting alcohol use, maintaining a healthy weight, and controlling blood pressure.
Source: The Guardian