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A study published in JAMA looks at coffee and tea intake and the risk of dementia.
Dr Mohammad Talaei, Lecturer in Life Course Epidemiology, QMUL, said:
“The paper reports a robust association, supported by strong methodological approaches, leveraging the exceptional advantages of these American longitudinal studies: large sample sizes, long follow-up, and, most importantly, repeated assessments of lifestyle factors at later stages of the life course. Interestingly, they not only showed a lower risk of dementia but also modestly better cognitive function, as assessed by subjective and objective measures. However, there are two major considerations in this study:
“1. Dementia has a long prodromal phase, and, as the authors have mentioned, reverse causation is a concern. It means that a decline in coffee drinking or reporting coffee drinking could be a consequence of cognitive decline rather than the assumption that exposure precedes outcome. They have done a 4-year lag analysis, which is insufficient given the long prodromal phase of dementia, but also a 12-year lag analysis that apparently showed similar inverse associations, which makes reverse causation a less plausible alternative explanation. Another approach I wish authors had considered to address reverse causation is to verify the inverse association with dementia in a subgroup of participants with the least evidence of cognitive decline over the first 10 years of their luxurious 3-4 decades of follow-up.
“2. The second topic is a common complexity in nutritional epidemiology. Dietary exposures are inherently substitutional (when people don’t eat something, they usually eat something else as a substitution): Associations with coffee and tea consumption may reflect beverage substitution rather than the effect of coffee and tea in isolation, as non-consumers typically replace them with other beverages or habits. To address this, the authors controlled the associations for tertiles of non-caffeinated sugar-sweetened beverage intake and categories of alcohol intake. While it is a reasonable first step and necessary, I am not sure if statistical adjustment can fully address the issue. Stronger controlling approaches, such as testing these associations among abstainers, could have strengthened the evidence for a potential benefit of coffee and tea for brain ageing.”
Prof Jules Griffin, Director of the Rowett Institute, University of Aberdeen, said:
“The paper by Zhang and colleagues is an impressive population study, following two large groups of US volunteers as they age to understand how coffee, tea and caffeine intake might influence our risk of developing dementia. What is impressive about this study is the number of people that are involved and the relatively high quality of data on diet across these people’s lifetime, allowing the authors to build up a picture of caffeine drinking across adulthood. Our current understanding of dementia is that things that happen in mid-life contribute to our risk of dementia, and this means studies have to follow volunteers for long periods of time. The authors find compelling evidence that regularly drinking of coffee and tea during our lifetime is associated with a smaller risk of dementia in later life, with the biggest differences being detected from the non-coffee and non-tea drinkers, and the other groups.
“While this is an impressive study in terms of scale, the reduction in risk is quite a small decrease and so my message would be that if people wanted to reduce their risk of developing dementia there are other things they could consider that would have a bigger effect – not smoking, doing exercise, and reducing the intake of saturated fat and free sugar in our diets. As with any study based on associations there is also the question whether coffee or tea consumption is just part of a wider dietary or lifestyle pattern – for example, what are the non-coffee drinkers drinking and doing instead?”
Prof Eef Hogervorst, Professor of Biological Psychology, and Director of Dementia Research, National Centre for Sports and Exercise Medicine, Loughborough University, said:
“This large study included 131821 female Nurses and male Health Professionals from 2 cohorts who were followed for up to 43 years. Of this group, 11 033 had developed dementia (8.3%), but higher caffeine intake was associated with lower risk of dementias. Participants were on average in early middle-age when they started the study. Women reported to drink a median of 4.5 cups of coffee or tea per day and men 2.5 cups per day at this time. Those who drank more caffeinated coffee were younger (which would be associated with lower dementia risk as the study progressed), but also drank more alcohol and smoked, and ate more calories, which could all have increased their risk.
“Drinking caffeinated coffee of around 2 to 3 cups per day (or 300 mg of caffeine) or 1-2 of cups of caffeinated tea was associated with the lowest dementia risk, as compared to the lowest caffeine intake and drinking decaf. Associations were strongest in those 75 years or younger at follow-up, with a 35% reduction in dementia risk (compared to a 19% reduction in risk for 75+). Drinking more caffeinate containing beverages was not associated with reduced risk. Effects on cognitive function (only assessed in the women’s Nurses Health cohort) were in a similar direction, but were very modest and non clinically significant. Here, decaf coffee consumption was also associated with worse verbal memory.
“There is good biological plausibility for protective effects of caffeine on brain function. Caffeine is an adenosine antagonist and thus inhibits the inhibitor (adenosine) of many activating and memory improving neurotransmitter activity. These neurotransmitters activities are reduced by age, neuronal dysfunction and loss and dementia pathology affecting cognitive decline (e.g. dopamine) and dementia (e.g. acetylcholine) symptoms. Caffeine acts on many other mechanisms associated with brain health and dementia, including reduction of inflammation and regulation of dysfunctional glucose metabolism. In people without dementia, lifetime consumption of >2 cups per day of caffeine was associated with lower levels of the toxic amyloid plaques (https://www.nature.com/articles/s41398-019-0604-5.pdf) seen in Alzheimer’s disease (AD), the most common form of dementia. Lastly, coffee and tea have many other anti-oxidant components and vascular benefits. Unfortunately, green tea, which is thought to be very beneficial for health due to its multiple compounds, was not investigated separately. It was odd that in this study only 1-2 cups of tea were associated with optimal risk reduction, but this could relate to people in the US perhaps consuming less tea than coffee.
“This study is not the first to investigate caffeinated drinks and long term reduction of risk of dementia and improved cognitive function. Meta-analyses showed an average 10% reduction in dementia risk with caffeine vs non caffeine consumers. However, this study attempted to investigate whether there were optimal intakes of caffeine for brain function. There are several potential reasons for the optimal caffeine intake dose. These could be related to enzymatic threshold effects in the metabolism of caffeine. The authors also pointed out that effects of very high caffeine dosages on interrupting sleep and promoting anxiety might counteract beneficial effects on brain function. The Yerkes-Dodson law already dictated in 1908 that when arousal becomes too high, mental performance start to decrease.
“Many people with hypertension or cardiovascular disease are advised to reduce their caffeine intake. This study controlled for hypertension and other medication and changes in caffeine intake from baseline. However, intriguingly, higher decaffeinated coffee intake was associated with faster verbal memory and subjective cognitive decline, both risk factors for dementia. This suggests that reverse causality was hard to rule out. People could have switched to decaffeinated coffee to counteract sleep issues (which become more common in midlife) or other health issues, such as elevated blood pressure or arterial fibrillation, also associated with cognitive impairments and later life dementia risk.
“Several studies have shown paradoxically – but similarly – that moderate caffeine intake also reduced cardiovascular disease risk. Cardiovascular disease shares many risk factors with dementia and AD. However, this data could also be affected by people stopping earlier with caffeinated coffee and/or switching to decaf on doctor’s advice to protect their heart health. Experimental studies have shown improved cognitive function, also in middle-aged people. But some suggested this (like smoking) was related to withdrawal effects in regular consumers who received placebo, rather than effects of caffeine per se. To further investigate this would require mediation analyses to detect whether cardiovascular risk (e.g. increase blood pressure, also that prior to medical intervention with antihypertensives) started before caffeine intake became lowered over time and/or whether people switched to decaf and whether that association better explains increased later life dementia risk.”
Prof Sarah Berry, Professor of Nutritional Sciences, King’s College London, said:
“This new study adds to the mounting evidence that coffee, consumed in moderate amounts, is likely to support long-term health. This large-scale study provides convincing data suggesting that caffeinated coffee and tea are associated with a reduced risk of developing dementia and slightly better cognitive performance. The results of previous research exploring this relationship have been mixed, so although this is a high-quality study, we need more research to reach firmer conclusions.
“Importantly, in the current analysis, the association of tea and coffee with cognitive performance was still present even after accounting for many other lifestyle and dietary factors.
“Historically, tea has been considered healthy, but some have looked at coffee more recently with suspicion. Overall, though, the totality of the evidence from observational studies show that coffee can support long-term health and reduce mortality.
“While we wait for more research into coffee’s links with dementia, the evidence that coffee can support general health is now quite strong. So, if you enjoy coffee, you don’t need to feel guilty, but if you don’t respond well to caffeine or you don’t like the taste, don’t worry, there are plenty of other ways to support your health.”
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 Mohammad Talaei: “I have no conflict of interest.”
Prof Jules Griffin: “I am a consultant for Sitryx, a company specialising in designing drugs to target immunometabolism – the company is looking at drugs for irritable bowel disease and psoriasis.
I have received funding from the European Union to investigate endocrine disrupting chemicals and hold a grant from UK Research and Innovation examining the health benefits of a fish diet.
I hold shares in GlaxoSmithKline and Haleon plc.”
Prof Eef Hogervorst: “I acted as a consultant for Proctor to investigate nutrients and memory.”
Prof Sarah Berry: “Chief scientist at ZOE (options and employment), active funding from Almond Board of California, Alliance for Potato Research, Cancer Research UK and British Menopause Society.”
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.