Is it true that acrylamide, a chemical formed during the roasting of coffee beans, transforms your daily cup of bliss into a deadly hazard?

^{Hmmm, coffee.... CC0, pixabay}

Intro

Cancer is without doubt a huge problem in modern society. In the second half of the 20th century, disease rates virtually exploded, and today it is the number one cause of death in the world. And it is also one of the few things in life that are still able to hit us from seemingly nowhere, and against which noone is shielded, no matter the precautions. Imo, it is therefore only natural to be afraid of cancer. And naturally, whole armies of scientists (and unfortunately also quacks) have set out in search of both cures and culprits - sometimes with considerable success. But in some cases, fear is also giving rise to strange blossoms...

The latest case: the acrylamide produced during the roasting of coffee beans is carcinogenic, and coffee drinkers must therefore be informed and protected!
At least this is the hypothesis that is becoming more and more popular, which has numerous followers especially in the USA (that I call - no offense - the "motherland of fear"), but which also sloshes across the Atlantic slowly and does not stop at our blockchain either. In California, coffee products must now even carry a warning sign!^Ref

^{Warning signs on coffee and in cafés in California... (If you want to call Starbucks a café...) CC BY-SA, Zach Copley}

And now it's time for a little confession: I am a huge coffeeholic. Below 3 cups I can't move, below 5 cups, I'm still useless. The darker and stronger, the better.
So naturally, this topic is of concern to me. Reason enough to take a closer look...

Acrylamide

Acrylamide is actually a mass chemical which is mainly used to produce a hardening gel which is excellently suited as a sealing agent and is used, for example, in tunnel construction. Bioscientists may also remember the countless failed Western blots that they had to endure during their early carreer… Because even in this standard method of molecular biology, polyacrylamide gels are used to separate proteins.
As you get more experienced, you learn how to delegate Western Blotting to your lab slaves students!

^{The chemical structure of acrylamide. Even anti-chemist will agree that it is a quite simple molecule.}

The toxicity of the chemical only really came to the fore in 1997, when large quantities were released into the groundwater during the construction of the Hallandsåstunnel in Sweden and several cows died in the surrounding area.^Ref Responsible for those deaths were the acute-toxic properties of acrylamide as a neurotoxin.

 

Please note: Acute toxicity is the immediate, not time-delayed effect of a poison, which usually requires relatively high doses and is reversible (at least up to a certain threshold) - i.e. after the symptoms have subsided, no or only minor damage remains. If you survive, naturally.
Bad luck for those cows…

In contrast, chronic toxicity is the delayed effect of a poison to which one is exposed in doses over a long period of time. The toxin's imperceptible effects add up over time and then cause a disease. The most "classic" among chronic-toxic effects: Cancer.

So why would I care about a tunnel sealing agent?

That's a valid question. If acrylamide were simply a chemical used as a building material, noone would be talking about it. One could simply use another sealant and mission accomplished.
Would be nice. Unfortunately, food chemists will tell you that there is the so-called "Maillard reaction".
This reaction occurs (to put it simply) when starch is strongly heated in the presence of proteins. Through them and various subsequent reactions, a multitude of different products are formed. This applies for desirable aroma components such as found in the bread crust, but also for false aromas (e.g. hyroxymethylfurfural in UHT milk) and then of course unwanted, because toxic substances, such as acrylamide. The Maillard reaction is the reason why we find acrylamide also in foods such as potato chips, crispbread or even coffee, where it is produced during the roasting process of the coffee beans.

Is acrylamid carcinogenic?

Now, the acute toxicity of the substance in food is not a problem, as the amounts of AA there are far too low to produce these effects in humans. But in the 2000s, a few studies seemed to show that acrylamide could be carcinogenic! And then, hell broke lose.

The whole excitement was kicked off by good old experiments with cultivated cells ("in vitro"). Several studies at the beginning of the 0's found out that acrylamide was able to act "genotoxic", i.e. being able to damage the DNA, which is often a precursor process to cause cancer.^{ref1, ref2, ref3}
As a follow-up, animal experiments were conducted quickly. And after genotoxic and carcinogenic effects were also found there,^{ref1, ref2} the WHO classified acrylamide as "probably carcinogenic", the authorities stepped on the scene and regulated the substance. This means that they set legally binding maximum values, up to which the compound is considered toxicologically harmless and permitted in food.

So far, so good. But why would good old Sco habe a problem with warning signs, then?

 

Well, my dear readers, the whole story is a little bit more tricky than that...

Because since then, science did not sleep. And so, there are now some epidemiological studies on the subject. These compare groups that take up very little of a substance with "high-risk groups" and examine whether there are health differences. In this case, we compare raw-eating water drinkers with crispbread-eating coffee addicts. Just as an example, of course. But man, would that be a funny study design. ;-)

And in these studies, there is absolutely no visible influence of acrylamide exposure on cancer risk. At least, this is the conclusion of a very extensive meta-analysis from the year 2015.^Ref
Now what is that, again? Since individual studies often produce contradictory results, depending on their exact execution, specialists wait until a sufficiently large number of publications (in this case more than 30 epidemiological studies) are available. Then, they perform a comprehensive analysis of all available data, which are weighted according to objective criteria (quality of design and execution, number of test subjects, size of observed population, etc.). The result in the specific case (as mentioned): zero influence on cancer risk.

If one compares strong coffee drinkers with abstainers, the former even have significantly fewer cardiovascular diseases, while the cancer risk is not influenced.^Ref And coffee-drinking rats have even less cancer.^Ref
Ok, ok, the last one is a single study, and not a meta analysis. But a fun study, anyway. A (for me) very satisfying result: This preventive effect worked neither with decaffeinated coffee nor with caffeine tablets!
Ha, take that, Mrs. "More than two cups are bad for you"!

But how can that happen? Wasn't acrylamide producing cancer in rats? Well...

Sola dosis facit venenum.

My homies know the sentence already. For all others: It is THE legacy of Paracelsus to mankind and means as much as: Only the dose makes the poison.
Studies in cell culture like to use completely unrealistic concentrations of a substance to clarify whether effects are possible at all. One of the studies that I quoted above was carried out under the supervision of my current boss. She only saw the DNA-damaging effect on human cells at a concentration of 6 mM (millimol/liter). Probably doesn't tell you anything, but I just say this much: The genotoxicity of some mold toxins, which occur in comparable amounts in food, is about 1000 times stronger in the comet assay. And I'm talking about non-regulated substances here. Some chemotherapeutics: Factor 1,000,000.

^{The unbelievable Paracelsus. Pic is public domain.}

In animals, scientists also wanted to show effects (after all, they performed an expensive and complex animal experiment, and one wants to be able to publish the data after such an ordeal), and went accordingly high with the concentrations. Then, the WHO had to classify acrylamide as probably carcinogenic (cancer-causing), which is also correct as in absurdly high doses, the substance IS carcinogenic), and the authorities see themselves forced to introduce limit values, which are safe. Correctly enough, in a way that consuming enough acrylamide to reach those illegal levels would require some effort. The German Federal Institute for Risk Assessment writes the following:

„It should be noted in this context that no clear epidemiological link between cancer and exposure to acrylamide has been established so far. It is possible that the risk of carcinogenesis - if present in humans - is practically undetectable at the given exposure.“^Ref

All correct, all quite normal, absolutely no reason for panic.

I can understand that scientific noobs in a hyper-nervous (American) society nevertheless come up with the idea that coffee is dangerous. They just don't know any better. But the fact that a judge in California comes up with the idea of giving this notion more than just a legitimate touch by ordering coffee houses to put up warning notices, I lack any understanding for. This is evidence of the arbitrariness of a justice system that pays more attention to emotional satisfaction than to facts and figures.

Conclusion

According to current scientific knowledge, coffee is most probably NOT cancer-causing, no matter the warning signs. So you can enjoy another cup tomorrow morning. Or two. Or three. Or, if your name is Sco, you can also enjoy four.

Disclaimer:
In my blog, I'm stating my honest opinion as a researcher, not less and not more. Sometimes I make errors. Discuss and disagree with me - if you are bringing the better arguments, I might rethink.

 

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