Aflatoxin B1: The Only Mycotoxin in IARC Group 1

What this is about

The word "carcinogen" causes fear. That is precisely why I want to explain it to you calmly and cleanly, instead of leaving it standing as a headline.

Aflatoxin B1 is the only mycotoxin the IARC places in its highest evidence class, Group 1. That is a statement about the strength of the evidence, not about your everyday life. Both belong together when you understand it correctly.

How I label evidence in this article

In vitro Cell studies In vivo Animal studies Human Human studies Clinical Practice experience

Aflatoxin B1 is among the best-studied mycotoxins of all. Unlike many indoor toxins, here there is a solid human data base and a formal regulatory classification by the IARC. Where I speak about accompaniment and metabolism, I label more cautiously.

From practice: a recurring pattern Clinical

When the liver values stay "slightly elevated" and no one asks further

I am not describing a single real fate here, but a pattern that I encounter again and again in practice. Imagine a person in their mid-forties, athletic, little alcohol, who has slightly elevated liver values over months. Ultrasound unremarkable, hepatitis serology negative, everything "within range".

"I was told it was nothing serious. But no one asked what I actually eat and how I store it."

What is often missing in such conversations is the simple question about habits. Large bulk packs of peanuts in the warm kitchen cupboard. Homemade nut butter that already tasted slightly bitter, but "shouldn't be thrown away". Spices as loose goods from holiday, for years on the damp shelf.

The turning point is rarely a single laboratory value. It is the changed question. Not "what is wrong with this liver", but "what does this liver regularly have to process".

Clarification: This is an anonymized, composite pattern, not a real individual case. I cannot claim isolated causality here. Slightly elevated liver values have many possible causes and should be clarified medically. Aflatoxin is only one of several conceivable factors one can think of.

What Aflatoxin B1 is, in one sentence

Aflatoxin B1 is a poison made by certain molds, above all Aspergillus flavus and Aspergillus parasiticus. It is not a substance the molds produce by accident. It is part of their chemistry with which they keep competition at bay.

The name reveals the origin. A. flavus means "the yellow one", and "A-fla-toxin" carries this mold in its name. The B1 stands for the fluorescence behavior under UV light, blue, and for the precise chemical variant. There are also B2, G1, G2 and a metabolite called M1. B1 is the best-known and most thoroughly studied form.

Origin

Aspergillus flavus and parasiticus

Two closely related molds that grow on heat-loving substrates. Indoors, A. flavus can occur after water damage. The main source worldwide, however, is food.

Target organ

Above all the liver

The liver is the central conversion organ. That is exactly where Aflatoxin B1 is metabolized, and exactly where the reactive intermediate arises that research describes as problematic.

Classification

IARC Group 1

The International Agency for Research on Cancer of the WHO places aflatoxins in Group 1, confirmed human carcinogen. The only mycotoxin in this highest evidence class.

Stability

Heat-stable

Aflatoxin B1 largely survives normal cooking, frying and baking. Cutting away visible mold spots is not enough, because the toxin may have spread into the part that looks clean as well.

What "IARC Group 1" really means, and what it does not

Here lies the biggest misunderstanding. Many people read "Group 1" and think: highest danger. That is not what is meant.

The IARC does not sort substances by danger in everyday life, but by the strength of the scientific evidence. Group 1 means: it is scientifically confirmed that this substance can cause cancer in humans. It does not mean that every encounter with it causes cancer. The same Group 1 also contains sunlight, alcohol and processed meat. No one would claim that a glass of wine is as dangerous as a high-dose poisoning.

Reframe

"Group 1" describes how certain the connection is, not how large your personal risk is. Your risk depends on amount, duration, accompanying factors and your own detoxification capacity. The classification is a scientific statement, not a prognosis for you. Precisely this distinction takes the fear out of the word and gives you the levers back.

And the word "only" is meant precisely here. Aflatoxin B1 is the only mycotoxin that falls into IARC Group 1. Other well-known mycotoxins such as Ochratoxin A or Fumonisin B1 are in Group 2B, that is "possibly carcinogenic", because the evidence in humans is weaker there. "Only" therefore refers exclusively to this classification, not to other toxins being harmless.

Human Regulatory document The IARC classification

Ostry and colleagues summarized the IARC classification of mycotoxins in 2017. Their result: aflatoxins, foremost Aflatoxin B1, are classified as Group 1, confirmed human carcinogen, above all in relation to liver cancer. For you this means: the connection is well documented, and precisely for that reason prevention pays off at the simplest point, food quality.

Ostry V et al. Mycotoxins as human carcinogens, the IARC classification. Mycotoxin Research. 2017. doi:10.1007/s12550-016-0265-7

How aflatoxin reaches the liver, and what happens there

Now it gets biological, and exactly here it also becomes understandable why the liver is the main topic. The liver is your chemical workshop. Everything you eat passes through it. It is built to remodel foreign substances so that the body can excrete them.

With Aflatoxin B1, precisely this protective mechanism becomes the weak point. Enzymes of so-called Phase 1, above all from the cytochrome P450 family, convert the toxin. In doing so a highly reactive intermediate arises, an epoxide. You can imagine it like a sticky hook that binds to everything nearby. To DNA as well.

Studies have described a characteristic change, a mutation in the gene TP53, often at a particular site called codon 249. TP53 is one of the most important protective genes of the cell. It is sometimes called the "guardian of the genome". It ensures that damaged cells are repaired or shut themselves down in a controlled way.

The picture behind it

Imagine TP53 as the referee inside every cell. It blows the whistle when something goes wrong, and sends a broken cell off the field. If the referee itself is damaged, the game can get out of control. This is exactly where the described aflatoxin effect sets in. That explains why research takes this toxin so seriously.

Human Liver and hepatitis B as an amplifier

In its assessments on nutrition, the WHO describes that the liver cancer risk from aflatoxin rises markedly when a chronic hepatitis B infection is present at the same time. Both factors reinforce each other. For you this means in practical terms: anyone who already has a burdened liver has more reason to take the avoidable aflatoxin source, food, seriously.

WHO. Guidelines for indoor air quality: dampness and mould. 2009, as well as WHO assessments of mycotoxins in nutrition. WHO regulatory document

Where Aflatoxin B1 occurs

The most important thing first: the main problem is not the home, but the plate. Unlike many indoor mycotoxins, the by far largest source is food.

Aspergillus flavus loves warmth and moisture. That is why aflatoxins arise above all in field crops from warm climate zones when harvest, drying or storage were not optimal. Indoors the mold can also appear after water damage, but then the spore and allergy side is usually in the foreground, less the high aflatoxin dose.

Main sources

Nuts and maize

Peanuts, pistachios, Brazil nuts, maize. Classic substrates for A. flavus, above all with warm, damp storage or long stockpiling.

Often underestimated

Spices and dried fruit

Chili, paprika powder, nutmeg, dried figs. Loose goods from holiday without controls are a recurring theme here.

Indirect

Milk via feed

If a cow eats contaminated feed, a breakdown product, Aflatoxin M1, can pass into the milk. For this too there are strict limits in the EU.

Reassurance in everyday life

EU controls

In the EU there are statutory maximum levels and regular controls. Everyday exposure from regular retail is therefore usually low.

Diagnostics: what works, and what does not

Here I have to be honest, and that is more important to me than a simple promise. There is no single test that proves an aflatoxin burden beyond doubt. Anyone who sells you that is simplifying too much.

What does exist are biomarkers, above all from research. Aflatoxin binds in the blood to the protein albumin and forms so-called AFB1-lysine adducts. These can be measured in specialized laboratories and indicate an exposure over the last few weeks. In the urine, aflatoxin metabolites and M1 can appear. In some mycotoxin urine profiles, aflatoxin is also determined.

Important context

A single laboratory value is never proving, neither positive nor negative. Urine tests can fluctuate depending on excretion and the preceding days. The overall picture counts: dietary and living history, complaints, baseline labs including liver values and, where appropriate, specialized diagnostics. Interpretation belongs in medical hands, not in a self-test protocol.

In practice I therefore first ask about the obvious: what do the supplies look like, how are things stored, was there water damage, how is the liver otherwise burdened. Often the story explains more than any single value. You can find more on the logic of urine diagnostics in the mycotoxin test spoke.

The PNEI lenses on Aflatoxin B1

In Clinical Psychoneuroimmunology I never look at just one organ, but at the interplay of the systems. With aflatoxin the liver is at the center, but it does not stand alone.

Metabolism and liver

The Phase 1 and Phase 2 balance of the liver decides whether the reactive intermediate is neutralized quickly. The glutathione system is central here. An empty glutathione store can shift the balance.

Immune system

In animal and cell models, aflatoxins also act in an immunomodulating way and can rather dampen the defenses. This may explain why chronic burdens rarely appear as a single symptom.

Epigenetics and cell protection

The described TP53 mutation is at its core an epigenetically and genetically tangible intervention in the cell's self-control. Here it becomes visible why protection at the source is more important than any later repair.

Environment and nutrition

Unlike with most mycotoxins, the main switch sits with eating, not in the wall. That is good news, because at this point you have a lot in your own hands.

How the liver neutralizes aflatoxin, and how not to burden it additionally

The liver has a built-in antidote system. In Phase 2 it attaches reactive intermediates to carrier molecules and makes them excretable. The most important of these is glutathione, the body's own detoxification molecule. Sulfur-containing amino acids are its building material.

From this follows a calm, unspectacular logic, no miracle cure. Anyone who wants to support the liver ensures a stable metabolism, a good protein supply with sulfur-containing building blocks and a plant-rich diet. Secondary plant compounds from cruciferous vegetables such as broccoli are associated in models with the activation of protective Phase 2 enzymes. This is a plausible mechanism and a hypothesis for humans, not a promise of cure.

Reframe

You cannot "detox" a liver as if it were a clogged drain. But you can stop making it constantly work against the current. Less constant burden, better building blocks, no stockpile mold. That is less spectacular than any detox promise, but it is what biology actually allows.

Safety note

Specific substances for liver support, such as high-dose N-acetylcysteine or glutathione preparations, belong in medical care. They are not a free pass to keep eating contaminated foods. The most important thing remains avoidance at the source. With abnormal liver values, medical clarification is always necessary before thinking of mycotoxins.

Three levers you have in your hands right away

Keep supplies small and store them correctly

Store nuts, dried fruit and spices cool, dry and in manageable amounts. Do not hoard. The longer and warmer something sits, the sooner A. flavus finds its conditions. Small packages are, for once, the more sustainable choice here.

Pay attention to taste and appearance and discard consistently

Spit out nuts that taste bitter or musty immediately and discard the whole package. Throw away moldy foods completely, do not save the "good part". The toxin spreads invisibly, and heating does not reliably destroy it.

Rely on origin and use variety

Prefer goods from controlled retail with limit testing, be cautious with loose imported goods. A varied diet spreads the risk instead of concentrating it on a single source. In case of water damage in the home, additionally think of Aspergillus and remediate professionally.

And now you know why this one word, "only", deserves neither panic nor indifference. It marks how certain science is about this toxin. And it shows you exactly the point at which you can achieve the most, namely with what regularly lands on your plate.

Frequently asked questions about Aflatoxin B1

What is Aflatoxin B1 anyway?

Aflatoxin B1 is a mycotoxin produced mainly by the molds Aspergillus flavus and Aspergillus parasiticus. The IARC, the WHO's cancer research agency, classifies it as a confirmed human carcinogen (Group 1). Among mycotoxins it is therefore the only one in this highest evidence class. The main target organ is the liver.

Why is it said that Aflatoxin B1 is the only confirmed carcinogen among mycotoxins?

The IARC assesses the strength of the scientific evidence, not the danger in everyday life. For Aflatoxin B1 the data from humans and animals are sufficient to place it in Group 1, confirmed carcinogenic in humans. Other mycotoxins such as Ochratoxin A or fumonisins are in Group 2B, possibly carcinogenic. Aflatoxin B1 is therefore the only mycotoxin in IARC Group 1. The word "only" thus refers only to this classification.

How exactly does it damage the liver?

The liver converts Aflatoxin B1 via Phase 1 enzymes (cytochrome P450) into a highly reactive epoxide. This can bind to DNA. Studies have described a characteristic mutation in the tumor suppressor gene TP53 (often codon 249). TP53 is an important control instance of the cell. If it is damaged, the cell's self-control can be disrupted. That is exactly why the liver is at the center.

In which foods is it found?

Mainly in peanuts, maize, pistachios, Brazil nuts, dried figs, spices such as chili and paprika, and in rice when storage was warm and damp. Through contaminated animal feed the breakdown product Aflatoxin M1 can pass into milk. In the EU there are statutory maximum levels that are regularly monitored, which is why everyday exposure from regular retail is usually low.

Can I get rid of aflatoxin by cooking or cutting away?

Only to a very limited extent. Aflatoxin B1 is heat-stable and largely survives normal cooking, frying and baking. Cutting away visible mold spots is also not enough, because the toxin may have spread into the seemingly clean part as well. The best protection is to completely discard moldy or bitter-tasting foods.

How is a possible burden determined?

There is no single proving test. In research and specialized laboratories, biomarkers are used, such as AFB1-lysine adducts in the blood or aflatoxin metabolites and M1 in the urine. In practice the overall picture counts: dietary and living history, complaints and laboratory values. A mycotoxin profile in the urine can be one building block, but is not meaningful on its own and should be interpreted medically.

Does a possible burden mean I will get cancer?

No. The IARC classification describes that a connection is scientifically confirmed, not that every exposure leads to cancer. The risk depends strongly on amount, duration, accompanying factors such as a hepatitis B infection and individual detoxification capacity. In regions with strict food controls such as the EU, everyday exposure is usually low.

What can support the liver in the processing?

Among other things, the liver uses the glutathione system and Phase 2 enzymes to neutralize reactive intermediates. A stable metabolism, good supply of sulfur-containing amino acids and secondary plant compounds, and avoiding further liver burdens can support this capacity. This is accompaniment of the metabolism, not a promise of cure. Specific substances belong in medical care.