Study doesn’t show tea and coffee cause lower dementia and stroke risk

“Keeping the cuppas coming reduces risk of stroke and dementia”

“Stroke risk: The drink to make at home that slashes your risk of the condition by 32%”

A study concluded that drinking two to three cups of coffee with two to three cups of tea per day is associated with about 30% lower risk of certain types of stroke and dementia. However, the authors clearly state that their research “cannot establish a causal relationship”. 

This means that contrary to the headlines of articles in The Daily Telegraph and The Daily Express, this study does not confirm that “Keeping the cuppas coming reduces risk of stroke and dementia”, or that tea and coffee “slashes your risk of the condition by 32%”.

Professor Tara Spires-Jones, UK Dementia Research Institute programme lead, told the Science Media Center that while the research is “interesting” and “robustly conducted”, it is “not possible to know from this kind of data whether the tea and coffee drinking are the cause of reduced risk of stroke or dementia”. 

She added there may be other factors in people that drink tea and coffee that are the “real influencers of disease risk”. 

What did the scientists do?

The study analysed data from over 365,680 participants in the UK Biobank. The UK Biobank is a large, biomedical database of over 500,000 people who have agreed to take part. It can be used by researchers for things like prospective studies, which follow a group of individuals over a period of time. This type of study can draw out associations, but, as there are so many other potential factors in people’s lives that can influence the outcome, it cannot be used to prove a particular cause.  

This particular study analysed the data of people who had strokes and dementia, and looked at their recorded tea and coffee intake. It found that two or three cups of tea as well as two or three cups of coffee per day were associated with a 32% lower risk of stroke, and a 28% lower risk of dementia.  Although the study did try to adjust or control for certain lifestyle factors or medical backgrounds, it could not say that tea and coffee consumption was the sole cause of the link as there may be other lifestyle factors involved.

Dr Rosa Sancho, head of research at Alzheimer’s Research UK, said: “Studies like this one are not able to pinpoint cause and effect, and while the researchers attempted to control for other factors that could affect a person’s risk of stroke and vascular dementia, no firm conclusions can be made about whether tea or coffee cause this lower risk.”

Study participants only recorded their tea and coffee at the beginning, as they were recruited into the study, so it does not include information about long-term habits.

We have previously written about the importance of media outlets clearly distinguishing between studies which show a correlation or link between two things, and those which show a cause. 

There are other things to think about with this study 

Although the study did report a link between a “moderate” tea and coffee intake, and a lower risk of stroke and dementia, it also showed that drinking lots of tea or coffee (more than eight cups of each) was actually associated with a higher risk than those who drank none. 

Again, this doesn’t prove that lots of tea or coffee actually caused these diseases.

The study also focused exclusively on participants who were enrolled between the ages of 50 and 74, and 96% of them were recorded as being white British. 

Dr Sancho said that we therefore “cannot infer an association that is relevant to everyone in the UK”.