The guide / Part 22

Coffee, tea and memory: what we know and what we don't

By The Prolongeva Editorial Team Written from the published research cited in each article Updated October 2026

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A strong coffee makes the morning sharper, and by 50 many of us suspect it is holding our memory together. It is fair to ask whether that is true. This guide separates what caffeine does within hours from what cohort studies link to dementia over decades, and says where the evidence stops.

What does caffeine do for attention in the short term?

Here the evidence is firmer, but it is about attention, not memory. A 2025 systematic review and meta-analysis (Kløve and Petersen, Psychopharmacology) pooled 31 randomized, double-blind, placebo-controlled trials with 1,455 participants. In healthy adults, caffeine improved both accuracy and reaction time on attention tasks, with small effect sizes (g = 0.27 and 0.28). These were pure caffeine doses, not coffee.

The authors reported larger gains at doses of 200 mg or more, and found the effect was not influenced by habitual caffeine intake. We read the abstract only, and the trials were short, so it says little about your memory next year.

A 2025 systematic review of 50 trials (Payne et al., Nutrition Reviews; 15 were pooled) found small differences favouring l-theanine plus caffeine, and l-theanine alone, on some attention and reaction-time measures in the first two hours. Confidence intervals were often wide, and the authors asked for research using real tea drinks. We read the abstract only.

What do long-term studies say about coffee, tea and dementia?

They point in a few directions. In a 2026 JAMA cohort (Zhang et al.), 131,821 participants from the Nurses' Health Study and the Health Professionals Follow-up Study were followed for up to 43 years. Higher caffeinated coffee intake was associated with lower dementia risk and modestly better cognitive function.

The strongest differences were at about 2 to 3 cups a day of caffeinated coffee or 1 to 2 cups of tea. Decaffeinated coffee showed no protective associations. We read the abstract only.

Other cohorts are less tidy. In a 2025 UK Biobank analysis (Rainey-Smith et al.; 8,715 dementia-free adults aged 60 to 85, mean follow-up 9.11 years), moderate coffee drinkers and moderate and high tea drinkers had slower decline in fluid intelligence. So did people who never drank coffee. The authors said randomized trials are needed to establish cause. We read the abstract only.

A 2026 UK Biobank cohort (Lin et al.; 134,425 participants, 13.5 years) reported that excessive coffee consumption was associated with higher risk of neurodegenerative disease, while tea intake was associated with lower risk. We could not see how that study defined excessive from the abstract.

Why is an association not proof that coffee helps?

Because these studies watch what people choose to do. They did not assign anyone to drink coffee. The JAMA authors themselves opened by saying evidence linking coffee and tea to cognitive health remains inconclusive.

In our reading, three things could be at work, and we cannot separate them:

• Who drinks coffee. People who drink it may differ in sleep, health, income or habits from people who do not. The two big US cohorts were health professionals.
• Reverse causation. Someone whose thinking is already changing might drink less coffee. That would make coffee look protective.
• Self-reported cups. Intake is usually recalled, not measured, and a cup varies in strength.

The results also disagree on details, as the UK Biobank studies above show. The evidence is mixed. We found no trial showing that drinking coffee prevents memory loss, and we are not telling you to drink more.

How do caffeine and sleep fit in?

The FDA lists insomnia or sleep disruptions among the effects of too much caffeine, alongside increased heart rate, heart palpitations, high blood pressure, anxiety and jitters. It also says people vary widely in how sensitive they are to caffeine and how fast they clear it.

In our reading, sleep matters for memory (see our sleep guide), so a drink that costs you sleep may not be a good trade. We cover that link in sleep and memory after 45. If you notice you sleep worse on afternoon coffee, that is worth acting on.

Does green tea contain caffeine, and what about extracts?

Yes. The NCCIH says no safety concerns have been reported for green tea consumed as a beverage by adults, but that green tea does contain caffeine. This matters if you are cutting caffeine for sleep or anxiety.

The NCCIH also says that, although uncommon, liver injury has been reported in some people who used green tea products, primarily green tea extracts in tablet or capsule form. A cup of tea and a concentrated capsule are not the same thing. The NCCIH page we read made no statement about green tea and memory.

Who should be careful with caffeine?

Pregnancy is the clearest case. The NHS says you should not have more than 200 mg of caffeine a day when pregnant, and that too much has been linked to a higher chance of miscarriage and stillbirth. Its examples: about 100 mg in a cup of instant coffee, 75 mg in a cup of tea, 40 mg in a can of cola. The FDA advises anyone pregnant, trying to become pregnant or breastfeeding to ask a health care provider whether to limit caffeine.

The FDA also says certain medical conditions and some medications make people more sensitive to caffeine. We found no list in that source. If you have anxiety, palpitations or a heart rhythm condition, or take regular medicines, ask a doctor or pharmacist about your own limit.

For the wider picture, see habits to protect memory and normal aging vs. early dementia. If forgetfulness is new or getting worse, a clinician can look at your case; a drink will not answer that.

This article is general information, not medical advice. If you are worried about your memory, your sleep or how much caffeine is right for you, please talk to a doctor or pharmacist.