Can Green Tea Prevent Dementia?
Probably not.
I love green tea. There’s something about the floral flavour that you just can’t get with anything else. Whether it’s a high-quality loose leaf pot or simply a teabag, the stuff is just somehow uniquely relaxing and wonderful.
And, according to recent headlines, my green tea habits could save my life. Or at least my brain. News reports are proclaiming that green tea is not just a titillation for your taste-buds - it can apparently lower your risk of dementia as well.
If you’ve been reading my work for a while, the next part will not surprise you. While the headlines are faithfully reporting the conclusions of a new scientific study, the data itself is extremely limited and there’s no good reason to believe that green tea can save your brain just yet.
Let’s look at the science.
Green Tea Data
The new paper is a large cross-sectional cohort study conducted in Japan. This is a type of study where researchers go out at a single point in time, and ask people a bunch of questions about their lives. They also usually do a range of medical tests, which in this case included brain MRIs.
The researchers then look at the associations between various things that they see in their dataset. In this study, the authors looked at the association between green tea and coffee drinking and different measures of brain volume as determined through those MRIs.
They found that there was a weak association between drinking more green tea - but not coffee - and having a type of brain issue that’s related to dementia. Specifically, people who drank more green tea had ~2% lower volume of white matter lesions, which are abnormal cell clusters in the brain that are associated with several types of neurological disease.
As far as epidemiological research goes, this study was pretty meh. Cross-sectional studies do not allow us to make many useful inferences, because they only tell us about disease states at a single point in time. It’s possible that the association seen between brain lesions and self-reported green tea drinking is caused by some third factor we don’t know about, or even that having slightly more brain lesions makes you less likely to drink green tea for some reason. We simply don’t know.
It’s also important to note that any headline talking about dementia was wrong. This study did not measure dementia. In fact, the researchers excluded people with dementia from the cohort. White matter lesions are indeed associated with the development of dementia, but even for people with 10x the rate of lesions seen in this study only around 20% develop dementia.
The decrease in lesions associated with green tea drinking was also extremely small. The researchers here used a formula that calculated the average volume of lesions divided by the average volume of the brain. On this measure, people who drank the least green tea - less than one cup a day - had a rate of 0.494%. People who drank the most green tea in the study - 3+ cups a day - had a rate of 0.478%. So if this study is accurate, and we take all of the results at face value, drinking about an extra pint of green tea per day would reduce the number of lesions in someone’s brain by around 0.014%.
That is…not a lot.
Bottom Line
To me, this reads like a classic hypothesis-generating study that tells us little to nothing new. People in Japan who report regularly quaffing gallons of green tea have slightly better brains than people who say they drink very little of the stuff, but that is almost meaningless in context. The study used three different types of measurement that looked at brain health, and only one showed the relationship, so it’s possible that this is just a statistical quirk anyway.
There are also several randomized trials showing that giving people green tea extracts does not seem to improve their mental health. For example, this 2015 study randomized a small group of people to get green tea extract or a placebo, and found no benefit on their measure of cognitive decline. Another much bigger 2024 study compared matcha powder to a placebo control and found that there were no improvements after 12 months for cognitive function.
It’s not impossible that green tea could improve your brain somehow, but it does seem a bit unlikely. In the words of Zuko from Avatar: The Last Airbender, tea is after all just “hot leaf juice”. It’s very tasty, and does contain a variety of phytochemicals, but unless you’re boiling the leaves for hours at a time you’re only extracting very small quantities of any chemicals that could potentially have a benefit.
If you like green tea, drink it. I will continue to do so regularly. Just don’t do it because of the headlines. Green tea probably does nothing for your risk of dementia.
I think green tea tastes disgusting but it would be good to know if it’s proven beneficial for anything else and also what, if any, foods ARE proven to help prevent dementia.
I drink 6 cups a day so 🤞🏻🤞🏻🤞🏻