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A new study has investigated whether drinking coffee or tea can reduce the risk of developing dementia, and the findings help explain some murky past results.
Researchers at Ningxia Medical University in China have found that some coffee or tea drinkers are lowering their risk of dementia.
But their observational study found that benefit was more likely for people with high blood pressure, who drank a certain number of cups a day. The type of coffee they sipped also seemed to matter.
The results come from the health data of more than 450,000 participants in the UK Biobank, who were followed for an average of 15 years. Roughly half were diagnosed with high blood pressure (hypertension).
Coffee drinkers with high blood pressure who said they consumed one-half to one cup a day had the lowest risk of developing any form of dementia, compared to those with the highest risk, who drank six or more cups daily.
Meanwhile, tea drinkers with hypertension, who had four to five cups a day, had the lowest risk of developing all-cause dementia, compared to those with the highest risk, who drank no tea at all.
Medical scientist Bo Wang and his colleagues chose to examine participants with high blood pressure because it's thought to accelerate cognitive aging and increase the risk of dementia.
"In this study, individuals with hypertension had a higher likelihood of developing dementia compared to the population without hypertension," write the researchers.
"The statistically significant association between coffee and tea consumption and the risk of dementia was more likely to be found in people with hypertension than in people without hypertension."
By managing modifiable risk factors like hypertension, some scientists estimate dementia cases could be cut by as much as 45 percent.
Coffee and tea – two of the most popular beverages in the world – could be one way to achieve this. But the new findings suggest dosage is crucial.
The research is only based on a correlation, so more studies are needed to dig into the potential effects of coffee or tea on the brain, whether good or bad.
The recent results do, however, help clear up some mixed findings from past observational studies, which did not account for the type of coffee or tea consumed.
Ground coffee as opposed to decaffeinated coffee, for instance, was associated with the lowest risk of all-cause dementia.
"The likely reason for this is that different types of coffee have different levels of caffeine, with ground coffee having the highest caffeine content, instant coffee the second highest, and decaffeinated coffee the lowest," the authors suggest.
Clinical studies are lacking, but some cell and animal studies have found that caffeinated beverages can lower the risk of hypertension, reduce inflammation, and maintain the blood-brain barrier, which keeps the central nervous system safe from toxins and pathogens.
Both coffee and tea share similar bioactive compounds, which can have anti-inflammatory or antioxidant effects. What's more, these beverages are linked to a lower risk of cardiometabolic disease like diabetes or hypertension, which could, in turn, lower the chances of dementia later developing.
"These benefits may slow down the progression of vascular inflammation, blood-brain barrier leakage, and beta-amyloid microvascular deposition in hypertensive patients, potentially delaying the onset of Alzheimer's disease," hypothesize the authors of the UK Biobank study.
Many questions remain to be answered, but based on emerging results, coffee and tea are beginning to attract significant interest from neurologists.
The study was published in Scientific Reports.
