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Many of us rely on a daily cup (or two) of coffee to boost mental focus and ward off fatigue.
It’s well-established that caffeine stimulates the central nervous system, increasing alertness.
Now, a decades-long study suggests that coffee may do more than increase mental sharpness over the course of a workday.
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According to the findings, a regular intake of caffeinated coffee may also protect long-term cognitive health.
Here’s what to know about the new study, plus how much daily coffee appears optimal for brain health. There’s good news for tea drinkers too.
About the new research
For the study, published Feb. 9 in JAMA, researchers from the Harvard T.H. Chan School of Public Health investigated the link between coffee and tea intake and dementia risk and cognitive function.
To do so, they analyzed data from 86,606 women who were part of the long-running Nurses’ Health Study and 45,215 men in the Health Professionals Follow-Up Study.
Participants, who were free of dementia and in their mid-40s (women) and early 50s (men) when the study began, were followed for 43 years.
During this time, detailed dietary information, which included daily intake of caffeinated coffee, tea and decaffeinated coffee, was collected every two to four years.
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Throughout the study, the researchers tracked participants who were diagnosed with Alzheimer’s disease or other types of dementia.
Participants also answered questionnaires that assessed their self-perception of worsening or more frequent memory loss or confusion.
As well, a subgroup of the Nurses’ Health Study participants underwent periodic cognitive testing to assess memory.
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Over the course of the study, 11,033 participants developed dementia.
Higher – versus lower – intakes of caffeinated coffee were associated with an 18 per-cent reduction in dementia risk, as well as a 15 per cent lower likelihood of self-perceived cognitive decline.
A higher intake of caffeinated coffee was also tied to better performance on cognitive tests.
Higher intakes of tea showed a similar protective pattern with dementia risk and cognitive function.
The most pronounced effects were seen with a daily intake of two to three cups of caffeinated coffee or one to two cups of tea.
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When researchers measured participants’ daily caffeine intake, higher intakes mirrored the findings associated with caffeinated coffee.
The researchers accounted for other factors that could influence dementia risk including family history, physical activity, diet quality, alcohol intake and the presence of depression, high blood pressure, high cholesterol and diabetes.
As well, the protective effect of caffeinated coffee and caffeine was observed regardless of whether participants carried the APOE4 genotype, the strongest genetic risk factor for developing late-onset Alzheimer’s disease.
There was no relationship between decaffeinated coffee intake and dementia risk or cognitive decline; drinking decaf didn’t increase or decrease the risk.
Strengths, caveats
The study is notable for its large sample size, lengthy follow-up period and repeated dietary measurements.
And unlike most previous studies on the topic, the researchers were able to distinguish between the effects of caffeinated and decaffeinated coffee.
The study was not able to capture the specific type of tea consumed – black versus green, caffeinated versus decaffeinated – or the specific coffee preparation methods, which can influence the concentration of protective compounds.
A key limitation, though, is the study’s observational design, which cannot prove caffeinated coffee or caffeine benefit brain health. Observational studies uncover associations only.
Even so, the new findings are consistent with many previous studies and meta-analyses reporting a protective relationship between coffee or caffeine intake and risk of dementia or cognitive decline.
How caffeinated coffee and tea may protect cognition
Coffee and tea contain many bioactive compounds, including caffeine and polyphenols, which may protect the brain by reducing inflammation, preventing oxidative stress caused by harmful free radicals and improving cardiovascular health.
Findings from animal studies have also shown that continuing exposure to caffeine can reduce the brain’s production of amyloid plaques and tau tangles: abnormal proteins that disrupt brain cell function.
Caffeine and caffeinated coffee are also thought to improve insulin sensitivity and reduce the risk of Type 2 diabetes, a major risk factor for dementia.
Should you switch to caffeinated coffee?
Evidence supports the notion that a habitual moderate intake of caffeinated coffee supports brain health, as well as cardiometabolic health.
So, if you drink a couple of cups of coffee each day, you don’t need to worry about cutting it out to stay healthy.
The current findings don’t, however, imply that if you abstain from caffeine, you should start consuming caffeinated drinks to reduce the risk of dementia.
For one, caffeine isn’t for everyone.
Caffeine can cause sleep disruptions, irritability and anxiousness, as well as trigger acid reflux symptoms. Caffeine sensitivity varies among individuals; some people experience negative effects with small amounts.
But importantly, including caffeinated coffee or tea in your diet should not overlook the big picture.
A brain-healthy lifestyle incudes following an anti-inflammatory diet pattern, engaging in regular exercise, getting proper sleep, staying cognitively and socially engaged and taking care of your cardiometabolic health.
Leslie Beck, a Toronto-based private practice dietitian, is clinical director of food and nutrition at Medcan.
