Can drinking coffee reduce brain size?

A recently published paper suggests so, but do their conclusions stack up?

Jonathan Adrian, MD
BeingWell

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Photo by Jakub Dziubak

Coffee is one of the most popular beverages worldwide. For some, they are a daily staple, used to boost performance and curb mid-day slumps. While others, including a growing body of coffee enthusiasts, enjoy them for the culture and distinct flavour profiles. Therefore, it is not uncommon for someone to end the day having consumed high volumes of coffee.

An article published in the Journal of Nutritional Neuroscience appears to have discovered some drawbacks to high coffee consumption. The paper has gained plenty of public traction despite having only been published in June and seems to be driving worry to coffee consumers.

Lead author Kitty Pham, who is a PhD candidate with the Australian Centre for Precision Health in the University of South Australia, analysed habitual coffee consumption on almost four hundred thousand participants in the United Kingdom and discovered a 53% increased risk of dementia in people who drink more than 6 cups of coffee a day compared to those who only consumed 1–2 cups a day.

How was the study performed?

This two-part study involved data from 398,646 participants aged 37 to 73 from UK Biobank, a large-scale biomedical database and research resource.

The first part of the study looked at disease risk by observing the number of subjects who developed dementia or suffered a stroke and then analysed the data alongside their coffee intake. This way, the researchers could determine associations between different categories of coffee intake and the risk of dementia or stroke.

In the second part of the study, researchers took a closer look at brain scans, which involved additional existing data from 17,702 participants. Directly studying brain imaging allowed Kitty Pham and colleagues to determine the association between brain volume and coffee consumption.

What did the results show?

Overall, they found an inverse linear correlation between coffee consumption and total brain volume. This means that subjects who consumed more coffee had smaller brain sizes, including the region that plays a major role in storing long-term memory — the hippocampus. The link between coffee consumption and dementia risk was rather dubious, however, as results demonstrate an equally high risk for decaffeinated coffee drinkers.

Evidence for stroke risk with high coffee consumption was weak, and the research concluded a 53% higher odds of dementia in groups who consumed more than 6 cups of coffee a day after adjusting for age, sex, BMI, blood pressure, and other lifestyle factors.

How can we take meaning from the results?

While the paper seems promising, there are some things to keep in mind.

First, the researchers failed to adequately distinguish the type of coffee beverage that was consumed. “Coffee drinkers” referred to those who reported intake of caffeinated coffee, without a clear distinction of ingredients that could profoundly alter the results, such as sugar content or the addition of milk. These differences were therefore not adjusted for, thus potentially confounding the results.

Second, although an association between coffee and caffeine was made, the study was not able to account for differences in caffeine content among coffee products. The Arabica species of coffee, for example, has half the amount of caffeine as the Robusta species. Taking this into account, “cups” of coffee might not be a suitable unit to illustrate total coffee consumption.

Moreover, the nature of the study only allowed researchers to see data at a single point in time and was therefore unable to actually witness changes in brain volume over time.

Dietary information produced by the participants was also sparse, adding to potential confounders as links between poor diet and dementia have been well established.

It is important to remember that the design of this study may allow researchers to determine associations, but not prove causations. Saying coffee and dementia risk are linked and coffee causes dementia are two different things.

And while the authors did posit a potential mechanism between caffeine and the observed changes in brain morphology, they also took into account other mechanisms that could have explained their findings, such as effects on the cardiovascular system. The authors inserted findings of another study, in which Li Cai and colleagues found that consumption of unfiltered coffee increases total cholesterol and triglycerides. Over time, these may clog up large arteries and if they occur in the brain, causes dementia. But coffee alone does not cause this. Other lifestyle factors, such as diet, exercise, and whether one smokes or not play more important roles in modulating blood lipid levels.

Wrapping it all up

Kitty’s paper has provided valuable insight and shall serve as a stepping stone for future researchers interested in tapping deeper into the long-term effects of high coffee consumption, which seems like a trend that’s only going to climb from here onwards.

Some notable studies to mention for coffee enthusiasts to guide your informational compass in the advent of this current research is a 2010 paper by Finnish researcher Marjo Eskelinen who found that moderate coffee drinking behaviour at midlife (3–5 cups/day) was associated with a 65% reduced risk of dementia in later life. Another surprising study, a 2019 meta-analysis by Youngyo Kim of Gyeongsang National University, demonstrated a reduced all-cause and cause-specific mortality of moderate coffee consumers (2–4 cups/day) compared to non-coffee consumers.

The evident take-home message from these papers encourages the age-long adage of “everything in moderation”. You might be able to get away with drinking more than 6 cups a day on occasion, but perhaps you’re better off with 2–3 cups a day. This of course, while we wait for future research to report back on the matter. Science is after all, quite fascinating.

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Jonathan Adrian, MD
BeingWell

Doctor, writer, photographer, and part-time social media strategist.