Written by Timothy Huzar — Fact checked by Alexandra Sanfins, Ph.D.
In a new study, researchers conclude that drinking coffee, tea, or both is associated with a reduced risk of dementia or stroke.
However, the research, which appears in the journal PLOS Medicine, does not demonstrate that coffee and tea directly cause decreased risk. Scientists will need to conduct more research to understand if the relationship is causal.
Although researchers have investigated links between coffee, tea, stroke, and dementia in the past, “considerable controversy” remains, as the authors of the new study explain.
Additionally, they write that “little is known about the association between the combination of tea and coffee and the risk of stroke and dementia and poststroke dementia.” The current study goes some way toward plugging this gap.
Dementia and stroke
According to the World Health Organization (WHO), over 55 million people around the world have dementia, and it is the seventh leading cause of mortality globally.
Dementia is a general name for a variety of symptoms characterized by progressive cognitive decline. It mainly affects older people.
The Centers for Disease Control and Prevention (CDC) point out that Alzheimer’s disease is the most common type of dementia.
According to the CDC, stroke is another leading cause of death. In the United States, more than 795,000 people experience a stroke each year.
A stroke occurs when the blood supply to the brain is blocked or a blood vessel in the brain bursts. This causes brain tissue to die or become damaged.
Stroke and dementia share around 60% of the same risk factors and preventive factors. Stroke also significantly increases the chances of developing dementia. Researchers have estimated that preventing people from having a stroke could prevent one-third of dementia cases.
Given the prevalence of dementia and stroke, scientists are interested to understand which lifestyle factors influence risk.
Tea and coffee consumption is one such lifestyle factor. Many people worldwide regularly drink tea or coffee, meaning that even a small potential effect could be significant at a population level.
In the present study, the authors note that some research has shown that drinking more tea or coffee is associated with a reduced risk of dementia. However, there is little research looking at whether a combination of tea and coffee is also associated with the same effect.
Further, the study authors point out that findings have been contradictory about whether coffee and tea consumption is associated with a reduced risk of stroke.
Consequently, the researchers conducted a study of the relationship between dementia and stroke risk and the consumption of tea, coffee, and a combination of tea and coffee.
Over 350,000 participants
The researchers drew on data from the U.K. Biobank, a database containing detailed medical and genetic information from 500,000 people in the United Kingdom.
They used data from 365,682 of these participants, recruited between 2006 and 2010. The researchers tracked their medical records until 2020.
When participants joined the study, they self-reported the amount of tea or coffee they consumed per day. The researchers then looked at how many participants experienced a stroke or developed dementia during the study period.
They also accounted for some other factors that may influence dementia or stroke risk. These included sex, age, ethnicity, educational qualification level, income, body mass index, smoking status, alcohol consumption, physical activity, diet patterns, certain biomarkers, and history of cancer, diabetes, cardiovascular arterial disease, and hypertension.
Overall, 5,079 participants developed dementia during the study period, and 10,053 had a stroke.
The researchers compared this data with the information on the amount of tea, coffee, or a combination of tea and coffee participants consumed.
They found that people who drank 2–3 cups of coffee a day, 3–5 cups of tea a day, or 4–6 cups of tea and coffee a day had the lowest risk of dementia and stroke.
Participants who drank 2–3 cups of tea and 2–3 cups of coffee per day were 32% less likely to have a stroke and 28% less likely to develop dementia when compared with participants who did not drink tea or coffee.
Importantly, while the study found an association between tea and coffee consumption and reduced risk of dementia or stroke, this does not mean drinking tea and coffee caused this reduced risk.
Medical News Today spoke with Professor Paul Matthews, O.B.E., M.D., Ph.D., center director at the U.K. Dementia Research Institute at Imperial College London, and a member of the U.K. Biobank steering committee. Professor Matthews was not involved in the study.
He explained that other factors not accounted for could affect the reduced risk of dementia and stroke among tea and coffee drinkers.
“This study describes a weak association of coffee and tea consumption with a lower risk of stroke or dementia in late life. The result is of interest as tea and coffee are rich in compounds called polyphenols that could contribute to the prevention of aging-related diseases.”
“However, the study cannot be interpreted as even suggesting that tea or coffee actually have a beneficial, protective effect.”
– Prof. Paul Matthews
“It is based on comparisons of participants in [the] U.K. Biobank who drink tea and coffee with those who do not,” Professor Matthews continued. “These populations differ in many ways. For example, tea and coffee drinkers are more likely to have a university degree and higher income.”
“While the authors have tried to address some of the recognized differences using statistical methods, they cannot control for those that they have not identified, [that is,] the ‘unknown unknowns.’”
“The report, therefore, while of interest, should not provoke changes in coffee or tea consumption for reasons of health,” suggested Professor Matthews.
Patrick Kehoe, Ph.D., professor of translational dementia research at Bristol Medical School in the U.K., also not involved in the study, supported this view.
Speaking with MNT, Professor Kehoe said, “there has been previous evidence of how coffee drinking was associated with increased lung cancer risk.”
“[However,] what came to light […] due to […] the timing of some of these studies was that smoking and tobacco might have been a hidden factor in those observations where people used to smoke with their social coffee, and in public areas where smoking is now increasingly banned.”
“For this case, things have moved on socially and [with regards to health], and so there are elements of tea [and] coffee drinking now that might [explain] why there are positive benefits.”
“For example, greater levels of socialization — which is thought to be protective against dementia — [and] exercise — which is better for the heart and mind — are associated with going to meet up with folk and could all be contextual elements behind these numbers. [This could include] less smoking now, too, which has also had a checkered history in terms of dementia risk but certainly would not have been good in terms of the cardiovascular risks and stroke risk as a result,” said Professor Kehoe.