A couple of teas or coffees a day could lower risk of dementia, scientists say | Medical research
According to researchers, people who drink a few teas or coffees a day have a lower risk of dementia and slightly better cognitive performance than those who avoid these drinks.
Medical records of more than 130,000 people showed that over 40 years, those who regularly drank two to three cups of caffeinated coffee or one to two cups of caffeinated tea per day had a 15 to 20 percent lower risk of dementia than those who did not drink them.
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 that habitual tea and coffee consumption is good for the brain, but research cannot prove this because caffeine drinkers may be less prone to dementia for other reasons. A similar link would emerge if poor sleepers, who appear to have a greater risk of cognitive decline, avoided caffeine to get a better night’s sleep.
“Our study alone cannot prove causality, but to our knowledge, it is the best evidence to date on coffee and tea consumption and cognitive health, and it is consistent with plausible biology,” said lead author Yu Zhang, who studies nutritional epidemiology at Harvard University.
Coffee and tea contain caffeine and polyphenols that may protect against brain aging by improving vascular health and reducing inflammation and oxidative stress, where harmful atoms and molecules called free radicals damage cells and tissues. Substances in drinks might 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 analyzed the records of 131,821 volunteers enrolled in two large American public health studies, the Nurses’ Health study and the Health Professionals Follow-up study. The two conducted repeated assessments of participants’ diet, dementia diagnoses, any cognitive decline they experienced, and objective cognitive test scores up to age 43.
Overall, men and women who drank the most caffeinated coffee had an 18% lower risk of dementia than those who drank little or none, with similar results seen for tea. The effect seemed to stabilize after two to three cups of caffeinated coffee or one to two cups of caffeinated tea. No link has been found between decaffeinated coffee and dementia.
Further work is needed to confirm whether both drinks actually protect the brain. Gold standard trials that randomly assign people to drink caffeinated or decaffeinated beverages for decades before testing for differences in dementia diagnoses are largely impractical. However, studies could determine whether the drinks cause biological changes related to brain function, which could be detected in scans or other tests, Zhang said.
Naveed Sattar, professor of cardiometabolic medicine at the University of Glasgow, said achieving this would not be easy, particularly because caffeine can have both positive and negative effects on the brain.
Both tea and coffee contain antioxidants that may be beneficial, and a caffeine intake can motivate people to work, learn, and exercise. In some people, caffeine increases blood pressure, an important factor in dementia. “Caffeine does a multitude of things, some that may be beneficial, some that may be harmful, and the net effect can never be estimated until you do a randomized trial,” Sattar said.
Researchers estimate that about half of the world’s dementia cases can be prevented or delayed by addressing 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 would say it is important to maintain a healthy lifestyle, exercise regularly, eat a balanced diet and sleep well to have better brain health.”
