People who have a couple of teas or coffees a day have a lower risk of dementia and marginally better cognitive performance than those who avoid the drinks, researchers say.
Health records for more than 130,000 people showed that over 40 years, those who routinely drank two to three cups of caffeinated coffee or one to two cups of caffeinated tea daily had a 15-20% lower risk of dementia than those who went without.
The caffeinated coffee drinkers also reported slightly less cognitive decline than those who opted for decaf and performed better on some objective tests of brain function, according to a report published in the Journal of the American Medical Association.
The findings suggest habitual tea and coffee drinking is good for the brain, but the research cannot prove it, as caffeine drinkers may be less prone to dementia for other reasons. A similar link would arise if poor sleepers, who appear to have a greater risk of cognitive decline, steered clear of caffeine to get a better night’s rest.
“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, and it is consistent with plausible biology,” said the lead author, Yu Zhang, who studies nutritional epidemiology at Harvard University.
Coffee and tea contain caffeine and polyphenols that may protect against brain ageing by improving vascular health and reducing inflammation and oxidative stress, where harmful atoms and molecules called free radicals damage cells and tissues. Substances in the drinks could also work by improving metabolic health. Caffeine, for example, is linked to lower rates of type 2 diabetes, a known risk factor for dementia.
The researchers analysed records of 131,821 volunteers enrolled in two big US public health studies, the Nurses’ Health study and the Health Professionals Follow-up study. Both took repeated assessments of the participants’ diets, dementia diagnoses, any cognitive decline they experienced, and scores on objective cognitive tests for up to 43 years.
Overall, men and women who drank the most caffeinated coffee had an 18% lower risk of dementia compared with those who had little or none, with similar results seen for tea. The effect seemed to plateau at two to three cups of caffeinated coffee or one to two cups of caffeinated tea. No link was found between decaffeinated coffee and dementia.
Further work is needed to confirm whether the two drinks actually protect the brain. Gold standard trials that randomly assign people to drink caffeinated or decaffeinated drinks for decades before checking for differences in dementia diagnoses are largely impractical. However, studies could explore whether the drinks drive biological changes linked to brain function, which could be spotted in scans or other tests, Zhang said.
Naveed Sattar, a professor of cardiometabolic medicine at the University of Glasgow, said getting clarity would not be easy, not least because caffeine can have good and bad effects on the brain.
Tea and coffee both contain antioxidants that may be beneficial, and a caffeine boost can motivate people to work, learn and exercise. In some people, caffeine raises blood pressure, a significant driver of dementia. “Caffeine does a multitude of things, some which may be beneficial, some which may be harmful, and the net effect can never be estimated until you do a randomised trial,” Sattar said.
Researchers believe about half of dementia cases worldwide can be prevented or delayed by tackling factors such as obesity, smoking, excessive alcohol consumption, hearing loss and high blood pressure.
“Don’t think of coffee or tea as a magic shield,” Zhang told the Guardian. “I’d say maintaining a healthy lifestyle, getting regular exercise, having a balanced diet and getting good sleep are all important to get better brain health.”
