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Discover: The science hidden in that savoury cup of joe

Can coffee improve your athletic performance? Are you a coffee pooper? Can coffee cure cancer?

You’re reading this with a cup of coffee in your hand, aren’t you? 

That’s okay; I wrote it with a mug next to my keyboard. In fact, coffee is the most popular drink in the world

Americans drink more coffee than soda, juice, and tea – combined – and much of the rest of the world follows suit. 

Given this popularity, it’s surprising how much confusion surrounds how this hot, dark, nectar of the gods affects our biology. 

Things start off pretty simply. The main biologically active ingredients in coffee are caffeine, a stimulant, and a suite of antioxidants. What do we know about how caffeine and antioxidants affect our bodies? The fundamentals are pretty simple, but the devil is in the details, and the speculation around how coffee could either help or harm us runs a bit wild. 

Let’s start on solid ground. The stimulant properties of caffeine mean that you can count on a cup of coffee to wake you up, as anyone who has enjoyed that first cup of morning coffee can attest. 

In fact, coffee, or at least the caffeine it contains, is the most commonly used psychoactive drug in the world

Caffeine is an organic molecule, a type of methylxanthine, consisting of two rings of carbon atoms. It seems to work as a stimulant, at least in part, by blocking adenosine, a naturally occurring molecule with a similar ring structure, from binding to its receptor and causing drowsiness. 

In the absence of caffeine, adenosine binds to this specific receptor molecule, triggering a chemical cascade that leads to drowsiness. In essence, caffeine acts as a molecular mimic, blocks the receptor, and prevents or postpones your body’s natural ability to be able a rest when you’re tired. 

This blocking is also the reason why too much coffee can leave you feeling jittery or sleepless. You can only postpone fatigue for so long before the body’s regulatory systems begin to fail, leading to simple things like the jitters, but also potentially serious complications like anxiety or insomnia

In fact, a possible link between coffee drinking and insomnia was identified over 100 years ago. The key is likely moderation.

Interestingly, caffeine’s stimulant effects can also improve exercise – enhancing strength, speed, and endurance – and caffeine is used by some athletes to improve athletic performance. There are, however, complications.

For one thing, at least in one study, coffee didn’t improve endurance, although caffeine did. 

Apparently, something in the coffee counteracted the positive effects of the caffeine. This varied biological response to the complex mixture that is coffee is a repeated theme.

Caffeine also improves strength performance, but not in all muscle groups, so that cup of coffee may or may not give you a better lift session depending on whether it’s a leg or chest day at the gym.

Further, caffeine also improves sprint performance, but only in people who have low regular coffee consumption – not in moderate to high coffee drinkers. So, that cup of coffee may, or may not, actually improve your workout depending on what the workout is, and how much coffee you regularly drink.

Now, let’s move into less firm territory. Will coffee make you poop? Is the poop-accelerating effect of a strong cup of coffee just anecdotal? Well, not according to at least one colleague who has stopped by for the occasional espresso, but this could be a psychology professor-limited phenomenon. 

Overall, the answer is a resounding “Maybe.” 

Coffee will wake you up, but it may or may not make you poop. A series of studies have shown that consuming coffee, or caffeine, absolutely induces bowel movements, but only in a fraction, maybe a third, of study participants.

In the same way that some people experience cilantro as a delicious herb and others as a soapy atrocity, apparently you’re either a coffee-pooper, or you’re not. 

Fundamentally, different people also just respond to caffeine differently. At least some of this variation is from different forms of that adenosine receptor, the molecule that caffeine binds to, and there are likely other sites of genetic variation as well. 

There are individuals who don’t process caffeine and to whom drinks like coffee could pose medical danger. Even away from those extremes, however, there is variation in how we respond to that cup of coffee. And, like much of biology, that variation is a function of environment, our past coffee consumption, genetics (things like the different forms of the adenosine receptor), and, honestly, just random chance. Biology is like that.

What can we say about the mechanism in the coffee-sensitive set? 

Coming back to the complexity theme, there may be a series of answers. In one study using rats, caffeine directly triggered smooth muscle contraction, so it is possible that caffeine directly promotes bowel activity. Other studies, though, have shown that decaf can have as strong an effect as regular coffee, suggesting a more complex mechanism involving some of the other molecules in coffee. 

We have to remember that biology is complex, and then continue questioning our preconceived notions. We may be interested in coffee because of the oh-so-joyous, caffeine buzz, but that doesn’t mean that caffeine is the most biologically interesting aspect of a good cup of coffee.

Whether you’re a coffee-pooper or not, there is, however, one absolutely sure-fire way for coffee to clear out your colon: a coffee enema. 

These sound horrific, but are, apparently, a “thing.” They even have their own Wikipedia page and celebrity endorsements

In fact, coffee enemas have been part of “alternative” approaches to cleansing and cancer therapy for almost 100 years. They were listed in the Merk Manual, considered to be the leading medical textbook, until 1972, and were referred to in the Royal Army Medical Corps Manual. They will definitely flush your bum, and just as definitely have no health benefits whatsoever.  Sorry, Gwyneth.

Let me be clear: do not under any circumstances flush your colon with coffee, at least not starting at the distal end. For one thing, that’s a waste of coffee and, if you’ll forgive me, even a crappy cup of coffee doesn’t deserve this fate. 

In fact, there is absolutely no evidence of any health benefits of coffee enemas. Most importantly, there is much evidence of their harm, including deaths directly attributed to the administration of coffee enemas (hopefully not directly mentioned in epitaphs).

The idea of these flushes, at least in part, is that they deliver the antioxidants in coffee more directly into the bloodstream, where they can then supposedly purify the body. They don’t, but the antioxidants in coffee may have positive health effects when delivered through more conventional ingestion.

Let’s move into even more shaky territory, the world of antioxidants and the buzz that surrounds them. Things actually start out pretty straightforward. Metabolism produces the energy necessary for life, but also creates waste, often in the form of oxidized molecules that can be harmful in themselves or by damaging other molecules. 

Antioxidants are a broad group of molecules that can scrub up the dangerous metabolic waste and all organisms produce antioxidants as part of their metabolic balance. It is unclear if supplementing our diet with additional antioxidants can augment these natural defenses, but that hasn’t stopped speculation. 

In fact, antioxidants have been linked to everything short of premature ejaculation, but, with apologies to Mel Brookes, that’s coming soon.

And, thanks to a quick Google search, I stand corrected, antioxidants have been linked to premature ejaculation. Are any of the claims of positive effects substantiated? 

We face an almost constant barrage of items that will supposedly “cure cancer,” including red wine, chocolate, even cigars (okay, not the last, those are just my guilty pleasure). Not surprisingly, coffee is also on this list.

Will coffee cure cancer? No, it absolutely won’t, but it may help to prevent it, and possibly some other diseases as well.

The Canadian Cancer Society is pretty clear, though. While the antioxidants in coffee may reduce the risk of some cancers, eating a healthy diet of fruits and vegetables is a much more efficient way to reduce your risk of cancer.

This is a good point, but, if we’re going to drink those cups of coffee anyway, are there any health benefits? 

Surprisingly, the answer is again a resounding “Maybe.”

Part of answering the question of coffee’s connection to cancer lies in asking another: what is cancer? That can be a complicated question in itself, but at its simplest, cancer is uncontrolled cell growth and uncontrolled cell growth is fundamentally about regulation, specifically regulation about when genes are, or are not, active.

My research group studies gene regulation and I can tell you that even a good cup of coffee, or boost of caffeine, won’t cause genes that are turned off or on at the wrong time to suddenly start obeying the Golden Rule. Probably, but I’ve been wrong before.

So, why “Maybe?” Because, the antioxidants in coffee may actually have a cancer fighting effect. Remember that antioxidants fight cellular damage. One type of damage that they may help reduce is mutations to DNA – and cancer is caused by mutations.

DNA mutations can result in the misregulation of genes, leading to tumor formation and cancer. The antioxidants in coffee have the potential to reduce the rate of cancer by reducing the amount of damage to DNA.  

This path is just what some studies have shown. Consuming coffee – and at least one of the antioxidants in coffee, chlorogenic acid – fights cancer in rats**.

Other studies in humans have shown that coffee consumption is associated with lower rates of some, but not all, cancers. 

Interestingly, coffee consumption has also been linked to reduced rates of other diseases as well. Higher coffee consumption is linked to lower rates of Parkinson’s disease and some other forms of dementia. 

Strikingly, at least one experimental study in mice and cell culture shows that the protection is a function of a combination of caffeine and antioxidants in coffee. The effect isn’t from one or the other, but from a combined, synergistic, effect***. Higher coffee consumption has also been linked to lower rates of Type 2 Diabetes

In a similar pattern to what we find in the cancer studies, results have varied across studies with some showing no association, while some others association with both regular and decaffeinated coffee. Overall, this variation suggests quite a bit of complexity, possibly reflecting the same kind of combined and interconnected effects of multiple coffee components that we see in the connection between exercise performance and Parkinson’s disease.

Coffee may also have a future in fighting diabetes, but as a drug delivery switch. Our bodies don’t make caffeine, and we only encounter it if we consume certain foods like coffee, tea, or chocolate. Interestingly, a group of researchers is harnessing this uniqueness to use caffeine, and potentially a cup of coffee, to potentially combat Type 2 diabetes. 

The researchers created an implantable device that included a genetically engineered construct that produced a small protein that stimulates insulin production under the control of a caffeine-dependent gene-switch.

Essentially, a cup of coffee could turn on insulin production. They showed that these constructs could effectively regulate insulin levels in diabetic mice. The study could lead the way to replacement of insulin injections. 

At the end of the day, where does this all leave us on the biology of coffee? Well, as I tell all of my students, it’s complicated. But, as most reading this already know, coffee will definitely wake you up in the morning. If you are part of the “lucky” 30 per cent, it will make you poop, and in some cases it may just help reduce your risk of contracting some diseases. 


*** Yan, 2018 Synergistic neuroprotection by coffee components eicosanoyl-5-hydroxytryptamide and caffeine in models of Parkinson's disease and DLB

Dr. Thomas Merritt is the Canada Research Chair in Genomics and Bioinformatics at Laurentian University.


About the Author: Dr. Thomas Merritt

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