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.

Aflatoxins are the only group of mycotoxins the IARC places in its highest evidence class, Group 1. Aflatoxin B1 is the best-studied and most potent single substance within that group. 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 Review summarizing work and regulatory documents

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"

Clarification first: this is not a real individual case and not a case history, but a general, composite pattern without numbers. I cannot claim isolated causality here. Slightly elevated liver values have many possible causes and belong in a complete medical work-up. Aflatoxin is only one of several conceivable factors one can additionally think of.

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".

What I often hear in such conversations, in substance and not as a quotation from any particular person: that the values were classified as nothing serious, and that no one asked about diet and storage.

The regular work-up does exactly the right thing here and is indispensable: ultrasound, serology, follow-up. What simply often has no room in a short appointment is the additional question about supplies, storage and 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. I have more time for that conversation, and that is the only difference I claim here.

First the regular work-up, and please complete it

Before thinking about mycotoxins with elevated liver values, the normal work-up belongs finished. That can include: fatty liver (MASLD), medicines and food supplements as a cause, iron stores and haemochromatosis, autoimmune hepatitis, Wilson's disease, alpha-1 antitrypsin deficiency, coeliac disease and the thyroid. In athletic people it is also worth looking at CK, because part of the values can come from muscle and not from the liver. Only when these paths have been worked through is the question about diet and storage a sensible addition, never a replacement.

What Aflatoxin B1 is, in one sentence

Aflatoxin B1 is a poison made by certain molds, above all Aspergillus flavus and Aspergillus parasiticus. Why the mold produces this poison is not conclusively clarified. It is discussed that it could help it against competition, against insects or against oxidative stress. What seems certain is only that it forms it deliberately and not by accident.

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 can arise 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. They are the only group of mycotoxins in this highest evidence class, and Aflatoxin B1 is the best-studied substance within it.

Stability

Heat-stable

Aflatoxin B1 is considered heat-stable. It only breaks down appreciably at temperatures well above what is reached in cooking, frying and baking. Heating therefore cannot reliably render it harmless. Cutting away visible mold spots is not enough either, 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" needs one more degree of precision here. The IARC does not list Aflatoxin B1 alone in Group 1, but the aflatoxins as a substance group, that is B1, B2, G1, G2 and M1. Aflatoxins are therefore the only group of mycotoxins in IARC Group 1, and Aflatoxin B1 is the best-studied and most potent single substance within it. 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. For Ochratoxin A, according to the same review, a reclassification is under discussion. "Only" therefore refers exclusively to this classification, not to other toxins being harmless.

Review, human and animal The IARC classification

Ostry and colleagues summarized the IARC classification of mycotoxins. Their result: aflatoxins, that is B1, B2, G1, G2 and M1, 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 can pay off at the simplest point, food quality.

This work summarizes the IARC assessments, it is not itself a regulatory document. The original document is IARC Monographs Volume 100F. The summary draws on epidemiological data, animal studies and mechanistic work.

Ostry V et al. Mycotoxins as human carcinogens, the IARC Monographs classification. Mycotoxin Research. 2017;33(1):65-73. 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 can arise, 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 can ensure that damaged cells are mended or shut themselves down in a controlled way.

Source for this section: IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100F, chapter on aflatoxins. IARC, Lyon 2012. [Regulatory document]

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, prospective cohort Liver and hepatitis B as an amplifier

In a prospective cohort from Shanghai with 18,244 men, Ross and colleagues found a strong interaction in 1992: aflatoxin markers in urine together with a chronic hepatitis B infection can raise the liver cancer risk considerably more than either factor on its own. For you this means in practical terms: anyone with chronic hepatitis B can particularly benefit from taking the avoidable aflatoxin source, food, seriously.

Ross RK et al. Urinary aflatoxin biomarkers and risk of hepatocellular carcinoma. Lancet. 1992;339(8799):943-6. doi:10.1016/0140-6736(92)91528-g

Besides hepatitis B, alcohol is among the most important factors that can raise the liver cancer risk, and the IARC places it in the same Group 1 as the aflatoxins. If you want to do something for your liver at one single point, that is usually the more effective lever than any question about supplies.

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 statutory maximum levels for aflatoxins apply, laid down in Regulation (EU) 2023/915, monitored through official food control. Everyday exposure from regular retail is therefore likely to be low in most cases. Objections still occur, above all with nuts and dried fruit from third countries.

Special situations

Pregnancy and breastfeeding: Aflatoxin M1 can pass not only into cow's milk but also into breast milk. Aflatoxin exposure during pregnancy is moreover associated with impaired growth of the child. Anyone who is pregnant or breastfeeding can pay particularly close attention to origin and storage with nuts, nut butter, dried fruit and loose spices.

Children: relative to body weight they take in more than adults, and nut butter and peanut products are typical children's foods. Here too, freshness counts more than stockpiling.

Very high single exposures can trigger acute aflatoxicosis up to liver failure. In Europe this is very rare, but with imported goods and stays abroad it is the reason why the disposal rule is not excessive caution. With acute nausea and vomiting, yellowing of skin or eyes, or clouded consciousness, this belongs immediately in emergency medical care, in an emergency via the emergency number 112, not in a practice appointment.

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 can 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.

These markers so far come predominantly from research. They measure a possible exposure, they say nothing about cancer, neither in one direction nor the other. A test can neither establish nor rule out a cancer. Anyone worried about the liver clarifies that through regular liver diagnostics and, if needed, through cancer screening, not through a mycotoxin profile.

I will also tell you what speaks against these tests. A critical review by Chang and Gershwin concludes that measuring mycotoxins in urine is so far not validated and has no documented relation to a clinical disease entity. I take that criticism seriously. That is why such a profile can, for me, only ever be one piece of the puzzle alongside history and baseline labs, never a proof and never the entry point into a treatment.

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.

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 can co-determine 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 can also influence the immune system, depending on dose and duration rather dampening or rather promoting inflammation. In humans this is not documented in the same way. It could explain why chronic burdens rarely appear as a single symptom.

Source for this paragraph: Sun Y et al. Toxins 2023;15(3):187. [In vitro, in vivo, review]

Genetics and cell protection

The described TP53 change is a real mutation in the genetic material, that is a letter swap in the gene itself, not merely a regulatory effect. Here it becomes visible why protection at the source can be 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.

Human, randomized trial What broccoli sprouts showed, and what they did not

For cruciferous vegetables there is even a randomized trial in humans. In Qidong in China, 200 adults drank an infusion of broccoli sprouts for two weeks. In the main result, aflatoxin DNA adducts in urine did not differ between the groups. Only in a secondary analysis did an association appear among those who absorbed the active compound particularly well. I mention it exactly like this, because it shows how thin the data are. Vegetables are good for many reasons. Protection against aflatoxin is not documented from this.

Kensler TW et al. Effects of glucosinolate-rich broccoli sprouts on urinary levels of aflatoxin-DNA adducts and phenanthrene tetraols in a randomized clinical trial in He Zuo township, Qidong. Cancer Epidemiol Biomarkers Prev. 2005;14(11 Pt 1):2605-13. doi:10.1158/1055-9965.EPI-05-0368

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 on the substances mentioned

A word on substances that are often named in this context. N-acetylcysteine is approved in Germany as a mucolytic and is pharmacy-only. Its use for liver support lies outside that approval, so it is off-label, and therefore belongs in medical prescription and care.

It is not a harmless substance. Gastrointestinal complaints are common, in asthma it can narrow the bronchi, with intravenous administration allergy-like reactions are described, caution applies with gastric ulcer, and it can enhance the effect of nitrates. Glutathione taken orally or as an infusion is not approved for this use. I deliberately do not give dosages here, that belongs in a conversation.

None of these substances replaces the most important thing, namely avoiding the source. And with abnormal liver values, the complete medical work-up always comes first, before thinking of mycotoxins.

Four 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 can spread the risk more broadly instead of bundling it on a single source. In case of water damage in the home, additionally think of Aspergillus and remediate professionally.

Know your hepatitis B status

This is the point with the strongest data in this whole text. Aflatoxin and a chronic hepatitis B can reinforce each other in liver cancer risk. Hepatitis B vaccination is among the standard vaccinations, and a simple blood test shows where you stand. Any family practice can do this. If you had to choose between the measures in this article, start here, not with the nuts.

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 the point at which you can achieve a lot in everyday life, namely with what regularly lands on your plate. The point with the strongest data, your hepatitis B status, please still take first.

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). The IARC lists the aflatoxins as a substance group here, that is B1, B2, G1, G2 and M1. They are the only group of mycotoxins in this highest evidence class, and B1 is the best-studied single substance within it. 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. Aflatoxins are therefore the only group of mycotoxins in IARC Group 1, and Aflatoxin B1 is the best-studied single substance within it. 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 considered heat-stable, it only breaks down appreciably well above the temperatures of 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. A critical review by Chang and Gershwin holds that measuring mycotoxins in urine is not validated and has no documented relation to a clinical disease entity. And independently of that: such a test can neither establish nor rule out a cancer.

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 such as N-acetylcysteine are not approved for this use, their use is off-label and belongs in medical prescription and care. I deliberately do not give dosages here.

How do I best protect myself from Aflatoxin B1?

Store nuts and dried fruit cool, dry and not for too long, spit out and discard anything that tastes bitter or musty, throw away moldy foods completely, pay attention to certified origin and do not hoard supplies. In case of water damage in the home, also think of Aspergillus flavus and remediate. A varied diet can spread the risk more broadly instead of bundling it on a single source. The point with the strongest data, however, is a different one: know your own hepatitis B status, because aflatoxin and a chronic hepatitis B can reinforce each other.