February 9, 2026

expert reaction to study looking at tea and coffee intake and dementia risk

A study published in JAMA looks at coffee and tea intake and the risk of dementia. 

Catey Bunce, Statistical Ambassador for the Royal Statistical Society, and medical statistician, said:

“This is an observational study, so it provides relatively limited evidence of association.  While it adds further data, the core message is not new. The way coffee and tea intake is categorised – particularly using different thresholds for men and women – risks confusion, and technical terms such as ‘non-linear inverse association’ are unlikely to be clear without further explanation.”

Dr Simon R White; Assistant Research Professor, University of Cambridge, said:

“From a research methods point of view, the definition of coffee consumption as quartiles and tea consumption as tertiles requires some care. Firstly, “high consumption” is relative to the data, not an absolute amount; this is a problem when transferring the findings of this US-based study to the UK, where surveys typically find the majority of people drink over two cups of tea a day – whereas this study has the “high tertile” as one cup of tea per day (Table 2).  Secondly, the coffee quartiles are defined within each single-sex dataset and are very different (Table 1, 4.5 and 2.5 cups/day for females and males respectively). The consequences of this are, although an association between coffee and tea consumption may exist it is hard to estimate the size of that effect in the UK from this paper.

“The paper clearly states that their findings are associations, with no substantive claims that coffee or tea consumption alone is the cause of the reduced risk of dementia or cognitive decline.  This type of finding is not new, a brief search reveals several research papers on this topic (for example using the UK Biobank to consider tea consumption). Investigating the effect of diet and its long-term implications is complicated, and this paper is not by itself sufficient to make recommendations on changing behaviours.”

Prof Kevin McConway, Emeritus Professor of Applied Statistics, Open University, said:

“This new study investigating possible associations between drinking coffee or tea and dementia isn’t the first one that has been done.  It does have several important advantages over previous studies – but that doesn’t mean that it answers every important question.  There are some awkward issues in interpreting its findings.

“The number of participants is big – nearly 132,000 individuals from two different major longitudinal studies of health workers in the USA.  They were followed up for a long time – 37 years on average (median).  So there’s more data, and data collected over a longer time, than previous studies generally had.

“One of the studies provided data on 45,200 male doctors, and the other provided data on about 86,600 female nurses.  (A warning for UK readers – the nurses’ study is called the Nurses’ Health Study, NHS for short, and that abbreviation in this research paper has nothing at all to do with our National Health Service.)

“The participants didn’t record their consumption of caffeinated coffee, decaf coffee and tea just once during the studies, as was usually the case in previous work.  They were asked about their consumption every 2 to 4 years.  This allowed the researchers to take into account changes over time in the amounts consumed.  That’s an advantage.

“Generally, I think that the statistical methods used are appropriate, are carried out properly, and are clearly reported.

“The researchers found evidence of association between the amount of caffeinated coffee and of tea that people drank and their risk of being diagnosed with dementia.  A lower risk of dementia was observed in people who drank moderate amounts of caffeine-containing drinks than in people who drank smaller amounts or none at all.  The evidence for an association between dementia risk and caffeinated coffee intake was clearest at moderate consumption levels, of two or three cups a day.

“The researchers did not find such evidence for drinking decaf coffee.  But, as I’ll explain, that doesn’t necessarily mean that it’s the caffeine content that actually causes the decreased dementia risk.  That’s certainly a possibility, but not the only one.

“The big snag with interpreting these findings is that this was an observational study.  People were not instructed to drink specific amounts of the beverages, but just did what they would have chosen to do anyway, and told the researchers about it.  But, unsurprisingly, the people who drank different amounts of the three beverages also differed from one another in terms of many other factors.

“One interpretation of the findings is that there’s something about caffeinated coffee, and about tea (which contains caffeine unless it has been decaffeinated), that causes people to have a rather lower risk of dementia.  But another possibility is that the difference in risk is actually caused by one of more of the other factors that also differ between the groups who drank different amounts of coffee or tea.

“The researchers were, of course, aware of that possibility.  They made statistical adjustments to try to allow for differences between people in a wide range of other factors on which they had data.  But that still doesn’t take away the possibility that the risk differences are caused by something other than people’s coffee or tea drinking habits.  The new research paper, rightly, makes this point explicitly.  Maybe the statistical model couldn’t adjust for a crucial factor because no data was available about it.

“Indeed generally the new research paper is very assiduous at pointing out alternative interpretations of the findings, that do not mean that consuming caffeine causes reductions in dementia risk.  None of these alternatives rules out caffeine as causing the risk reductions – but they make it clear that there are several other possibilities.

“For example, they mention the possibility that some people may change from caffeinated to decaffeinated coffee because they develop some health concern that in turn increases their risk of cognitive decline.  Because of the fact that consumption was measured and analysed statistically over time, this could be the reason for the lack of association between decaf consumption and dementia.  The group of participants who drink more decaf possibly don’t have a lower dementia risk than those who drink no decaf, simply because the group who drink more decaf contains more people who have changed to decaf because of some other health condition that itself increases dementia risk.

“That’s a bit complicated, but it is a possible pattern of cause and effect that has nothing direct to do with caffeine, and again it’s good that the researchers mention that it’s not ruled out by their findings.  But it still does leave open the possibility that it’s some other property of caffeinated coffee, rather than its caffeine content, that is the cause of the risk reduction.

“The researchers also mention other possibilities for the way cause and effect could work.  For instance, if people experience health changes that don’t amount to the start of dementia, but are part of a process that will later lead to dementia, that could cause them to be less accurate at reporting their food and drink consumption.

“The researchers do list several possibilities for the mechanisms inside the body that could lead to caffeine having a protective effect against dementia, but this study (and the underlying studies from which it drew its data) do not provide any direct evidence about these mechanisms.  That would have to come from different kinds of research.

“How big is the risk difference anyway?  Is it large enough to matter?  As part of their analysis, the researchers split the participants into four groups, in terms of how much caffeinated coffee they reported that they drank daily.  In group with the lowest consumption, mostly people who never drank it at all, about 12 in every 100 participants had a dementia diagnosis during the follow-up period of around 40 years.

“Now think of a group of 100 people who were similar, in terms of the characteristics used in the statistical analysis, except that they drank the same amount of caffeinated coffee as the quarter of participants in the whole study who drank the most caffeinated coffee daily.  (That’s about 3 cups a day, on average, though the quantity differed between men and women).

“In this new group of 100, according to the researchers’ analysis, about 10 would have a dementia diagnosis.  Of course we still don’t know whether it’s the caffeine in the coffee that is the actual cause of the risk difference.  This figure takes into account the statistical adjustments that were made to allow for differences between the four groups on other factors, so as to make a fair comparison.

“Is the difference, between 12 dementia diagnoses in those who drink the least caffeinated coffee and 10 diagnoses in those who drink the most, large enough to be a matter of concern, to the extent that people should be advised to drink caffeinated coffee and tea?  I think that’s rather difficult to say, given the doubt that inevitably remains about what is causing what.”

Prof Tara Spires-Jones, Division Lead in the UK Dementia Research Institute, Past President of the British Neuroscience Association, and Professor of Neurodegeneration at the University of Edinburgh, said:

“This study led by scientists at Harvard Medical School looked at data from over 130,000 people to examine whether caffeine intake is associated with dementia risk.  They observed that greater intake of caffeinated coffee or tea was associated with lower risk of developing dementia.  In their data, drinking 2-3 cups of caffeinated coffee or 1-2 cups of tea per day was associated with the lowest dementia risk with no further benefit to drinking more caffeine. 

“This is a well-conducted study that looked at data from a large number of people over many years.  However, the study does have important limitations.  This kind of observational research cannot prove conclusively that caffeine intake was the reason for lower dementia risk, other factors related to coffee and tea drinking habits could be responsible.  For example, sleep disruption and several cardiovascular health factors are associated with increased risk of dementia and these can affect people’s choices around caffeine intake.  Further, the data on caffeine intake were from self-reported questionnaires administered every 2-4 years, and if people were in early stages of dementia, they might have difficulty accurately reporting their intake or the early brain changes could affect behaviour including caffeine intake.”

Prof Naveed Sattar, Professor of Cardiometabolic Medicine/Honorary Consultant, University of Glasgow, said:

“This is a well‑conducted study for the type of data available.  However, because it uses observational, not experimental, evidence, the findings can only be considered suggestive.  A major concern is residual confounding: unmeasured factors that cannot be fully accounted for.  In this case, people who drink moderate amounts of tea or coffee may simply lead more balanced, healthier lives overall, and it may be these broader lifestyle patterns – not the drinks themselves – that relate to better brain health.

“There is currently no strong evidence from randomised trials that tea or coffee meaningfully improve recognised risk factors for brain health, such as blood pressure, cholesterol, or glucose levels.  For these reasons, I would interpret these findings with considerable caution.

“The fundamentals of protecting brain health remain unchanged: maintaining good cardiovascular risk factors, eating a healthy diet, staying physically active, keeping alcohol intake low, and engaging in regular mental stimulation.”

Dr Susan Kohlhaas, Executive Director of Research and Partnerships, Alzheimer’s Research UK, said,

“This long-running study suggests that people who regularly drank moderate amounts of coffee or tea were less likely to develop dementia later in life.  The lowest dementia risk was seen in people drinking around two to three cups of coffee or one to two cups of tea a day.  This level of caffeine intake also linked to slightly better scores on memory and thinking tests, although the differences were small.

“This research doesn’t prove that coffee or tea protect the brain.  This study shows an association, not a cause-and-effect relationship.  People who drink coffee or tea may also differ in other ways that affect brain health, even after careful adjustment, and the study relied partly on self-reported diagnoses.  It was also conducted in relatively similar groups of health professionals, which limits how widely the results can be applied.

“There’s no single food or drink that can prevent dementia.  Funding more research will be key to understanding what really reduces risk and how dementia develops over time.  In the meantime, anyone who wants practical, evidence-based ways to look after their brain health can take Alzheimer’s Research UK’s Brain health check-in.”

‘Coffee and Tea Intake, Dementia Risk, and Cognitive Function’ by Yu Zhang et al. was published in JAMA at 16:00 UK time on Monday 9 February 2026. 

DOI: 10.1001/jama.2025.27259

Declared interests

Dr Simon R White: “Industry link: Member of advisory board for CentileBio (CENTILE BIOSCIENCE INC.); https://centilebio.com/.”

Prof Kevin McConway: “I have no conflicts of interest to declare.”

Prof Tara Spires-Jones: “I have no conflicts with this study but have received payments for consulting, scientific talks, or collaborative research over the past 10 years from AbbVie, Sanofi, Merck, Scottish Brain Sciences, Jay Therapeutics, Cognition Therapeutics, Ono, Novo Nordisk, and Eisai, and direct a company Spires-Jones Neuroscience, Ltd to act as a consultant.  I am also Charity trustee for the British Neuroscience Association and the Guarantors of Brain and serve as scientific advisor to several charities and non-profit institutions.”

Prof Naveed Sattar: “NS has consulted for and/or received speaker honoraria from Abbott Laboratories, AbbVie, Afimmune, Amgen, AstraZeneca, Boehringer Ingelheim, Carmot Therapeutics, Eli Lilly, Gan & Lee, GlaxoSmithKline, Hanmi Pharmaceuticals, Janssen, Kailera, Mass Medicines, Menarini-Ricerche, Merck Sharp & Dohme, Metsera, Novartis, Novo Nordisk, Pfizer, Regeneron, Roche, Sanofi, UCB Pharma and Verdiva Bio; and received grant support paid to his University from AstraZeneca, Boehringer Ingelheim, Novartis, and Roche.  No shares in any medical areas.”

Dr Susan Kohlhaas: “Dr Kohlhaas has no declarations of interest.”

For all other experts, no reply to our request for DOIs was received.