People who routinely drink between two and three cups of caffeinated coffee, or one to two cups of caffeinated tea, each day have been found to have a 15-20% lower risk of dementia, according to new research.
The findings, published in the Journal of the American Medical Association, are based on an analysis of health records from more than 130,000 volunteers followed for up to 43 years as part of two major US public health studies.
Those who consumed the most caffeinated coffee were shown to have an 18% lower risk of dementia compared to those who drank little or none. The researchers observed a similar association for tea, with the apparent protective effect plateauing at the stated consumption levels. No link was found between decaffeinated coffee and dementia risk.
Alongside the lower dementia risk, caffeinated coffee drinkers also reported slightly less cognitive decline than decaf drinkers and performed marginally better on some objective tests of brain function.
Causality not proven, researchers caution
The study’s authors stress that their work cannot prove that the drinks themselves cause the reduced risk. Lead author Yu Zhang of Harvard University noted the research is “the best evidence to date” on the topic but said it does not prove causality, as published by The Guardian.
It is possible that caffeine drinkers are less prone to dementia for other reasons. For instance, if poor sleepers—who may have a greater risk of cognitive decline—avoid caffeine to aid their rest, it could create a similar observational link.
Professor Naveed Sattar of the University of Glasgow echoed the point, stating that caffeine has a multitude of effects, some potentially beneficial and some harmful, and that a randomised trial would be needed to estimate the net effect.
Plausible biological mechanisms suggested
The report suggests plausible biological reasons why habitual consumption might be beneficial. Both coffee and tea contain caffeine and polyphenols, which may protect against brain ageing by improving vascular health and reducing inflammation and oxidative stress—a process where free radicals damage cells.
Substances in the drinks could also work by improving metabolic health. The researchers note that caffeine, for example, is linked to lower rates of type 2 diabetes, which is a known risk factor for dementia.
Professor Sattar added that tea and coffee contain antioxidants that may be beneficial and that a caffeine boost can motivate people to work, learn, and exercise, though in some people it can also raise blood pressure—a significant driver of dementia.
Future research and lifestyle emphasis
Yu Zhang said further work is needed to confirm whether the drinks actually protect the brain. While decades-long randomised trials assigning people to drink caffeinated or decaffeinated beverages are largely impractical, studies could explore whether the drinks drive biological changes linked to brain function that might be spotted in scans or other tests.
Zhang emphasised that coffee or tea should not be thought of as a “magic shield”. He stated that maintaining a healthy lifestyle, getting regular exercise, having a balanced diet, and getting good sleep are all important for better brain health.
The research aligns with a broader medical understanding that an estimated half of dementia cases worldwide could be prevented or delayed by tackling factors including obesity, smoking, excessive alcohol consumption, hearing loss, and high blood pressure.
