Ochratoxin A: The Kidney and Brain Toxin Profile

What this is about

Ochratoxin A is not an exotic poison from the lab. It is one of the most frequently detected mycotoxins in food. It is also found regularly in damp indoor environments, there alongside other toxins and in strongly varying amounts.

This profile sets out where OTA comes from, why it particularly affects the kidney and brain, why it stays so long and what you can do from my point of view, without falling into panic.

How I label evidence in this article

In vitro Cell studies In vivo Animal studies Human Human studies Meta Review article

The mechanistic data on OTA come predominantly from cell and animal models. They are consistent across many studies. Direct human studies on chronic OTA exposure are limited. I label transparently.

Before you read on

How this article is meant

There is a constellation that is discussed again and again in environmental medicine: persistent concentration problems and exhaustion alongside a high moisture load in the home. Whether a connection really exists in an individual case can only be clarified medically and never derived from a description on the internet.

Please read the following sections as background knowledge, not as a description of your case. If you have symptoms, the work-up belongs in a consultation, and it should follow the common causes first. I come back to those explicitly at two points in this article.

And please do not stop any medically prescribed therapy and do not postpone any planned work-up because of this article.

The profile at a glance

Before we go into the biology, here are the most important key facts. If only one thing should stick with you: OTA is widespread, it is tough, and it affects more than just one organ.

Name

Ochratoxin A, OTA for short. One of several ochratoxin variants, by far the most important.

Producers

Moulds of the genera Aspergillus (above all A. ochraceus, in subgroups A. niger) and Penicillium (above all P. verrucosum in temperate climates).

Main dietary sources

Grains and grain products, coffee, wine and grape juice, dried fruit, spices, cocoa, partly beer.

Main indoor sources

Prolonged dampness, water damage, mould behind wallpaper, in bathrooms, basements and air conditioning systems.

Uptake

Through food, through the airways (spores and spore-bound toxin), partly through the skin.

Main organs

Kidney (most strongly emphasised), brain and nervous system, liver, immune system.

Residence time

Unusually long. Strong albumin binding and enterohepatic circulation. The plasma half-life in humans was calculated as around 35 days in an investigation in one single volunteer, so on a very narrow evidence base.

IARC classification

Group 2B, that is possibly carcinogenic to humans. Tumour-inducing in animal studies, not established in humans.

Clarification on the cancer reference

So that no misunderstanding arises here: Group 2B means that the evidence for a carcinogenic effect in humans is not sufficient to establish it. It does not mean that OTA causes cancer in humans. The professional discussion is not closed, either. Ostry and colleagues point out that newer data on OTA DNA adducts and on epigenetic factors could lead to a reclassification.

I expressly do not offer cancer screening, cancer prevention or cancer treatment in this context. Oncological and general practice prevention programmes are responsible for that, and nobody should postpone them because of this article.

Where Ochratoxin A comes from

You probably breathe in and eat OTA more often than you would like. This is not scaremongering. It is biology. The fungi that produce OTA are everywhere it is damp and nutritious.

On the food side it is above all grains, coffee, wine, dried fruit and spices. OTA often does not arise only at the consumer stage, but already during cultivation, harvest and above all damp storage. Coffee is a special case, because many people drink it daily. The exposure varies greatly, however, depending on cultivation, processing and storage.

On the housing side OTA becomes relevant when Aspergillus and Penicillium grow on damp building materials. After water damage, in a poorly ventilated bathroom, behind a cold exterior wall. Here you meet OTA not through the plate, but through the air you breathe in every day. It is precisely this silent, lasting indoor exposure that a short consultation rarely has room for. That is not a reproach to colleagues, that is a question of time and remit. A longer history has room for it, and sometimes exactly this question opens the door.

Reframe

OTA is not a rare poison, but a permanent guest. The question is rarely "am I even exposed", but "how high is my dose over time, and how well can my body process it". This shifts the view from fear towards concrete levers.

Why the kidney of all organs

Picture the kidney as a highly sensitive filter that presses the blood through thousands of times a day. What is dissolved in the blood passes through here. And OTA is very well dissolved in the blood, because it binds firmly to albumin. This inevitably makes the kidney the place where it arrives.

The tricky part: on current understanding the cells of the kidney tubules can actively take OTA up via transport systems, much as they do with other small molecules. In this way OTA can accumulate in precisely these cells. There it can trigger oxidative stress, mitochondrial damage and programmed cell death in cell and animal models. Over a long time this can impair the function of the fine filter units.

In vitro In vivo Review article OTA and the kidney cell

Khoi and colleagues bring together in 2021 what is known about the kidney effects of Ochratoxin A. Their review describes the kidney as the organ most strongly affected in the models evaluated. Among the pathways described are uptake via organic anion transporters, oxidative stress, disturbed autophagy and various forms of cell death. For the kidney this can mean that the sensitive filter cells perform their task less well under a lasting OTA load.

This work is a review of many individual studies from cell and animal models, not a measurement of its own in humans.

Khoi CS, Chen JH, Lin TY, Chiang CK, Hung KY. Ochratoxin A-Induced Nephrotoxicity: Up-to-Date Evidence. Int J Mol Sci. 2021;22(20):11237. doi:10.3390/ijms222011237 [In vitro, In vivo, Review article]

Important for context: these findings come overwhelmingly from cell and animal models. In humans the direct proof that everyday OTA amounts cause kidney diseases has not been conclusively established. It remains a justified suspicion with a consistent mechanistic basis. And precisely for that reason I deliberately phrase this in the conditional here: OTA can burden the kidney, it is not an automatism.

If your kidney values are abnormal, please in this order

A clear order matters to me at this point, so that this article puts nobody on the wrong track. If your kidney values are abnormal, the common causes belong in a work-up first.

These include diabetes, high blood pressure, inflammation of the renal corpuscles, regular use of painkillers such as ibuprofen or diclofenac, an obstruction to urine flow, pronounced dehydration and rarer bone marrow disorders with abnormal protein production. That is a matter for your general practice or a nephrology practice.

Only if that trail leads nowhere and a moisture load is on the table at the same time is the additional look at mycotoxins worthwhile. Please not the other way round. With a progressive kidney disease, lost time cannot be made up.

Why the brain too can be affected

Many people with mould exposure do not describe the kidney first. They describe the head. The fog. The feeling of thinking behind frosted glass. OTA is one of the mycotoxins that can mechanistically explain why quite well.

OTA is small and readily soluble. In animal models it can cross the blood-brain barrier and accumulate in brain regions. There the same damage patterns are described as in the kidney: oxidative stress, mitochondrial damage, inflammatory processes in the nerve tissue and a loss of nerve cells. The brain depends on a stable energy supply. When the power plants of the nerve cells suffer, clarity suffers.

In vitro In vivo Review article OTA and nerve cells

Obafemi and colleagues summarise in 2023 how Ochratoxin A can act on nerve cells. In cell models using human neuroblastoma cells, mouse hippocampal cells, astrocytes and microglia, and in animal models, OTA can trigger oxidative stress, inflame nerve tissue and drive cells into programmed cell death. The work additionally reports human biomonitoring data on OTA levels in blood plasma in people with neurodegenerative diseases.

Those are observations, not proof of a cause. And this work is a review of many individual studies, not a measurement of its own.

Obafemi BA, Adedara IA, Rocha JBT. Neurotoxicity of ochratoxin A: Molecular mechanisms and neurotherapeutic strategies. Toxicology. 2023;497-498:153630. PMID: 37709162. doi:10.1016/j.tox.2023.153630 [In vitro, In vivo, Review article]

In vitro In vivo Review article Mycotoxins and neuropsychiatric symptoms

Ratnaseelan and colleagues summarise in 2018 how mycotoxins can act on neuropsychiatric symptoms and immune processes. At the centre of that work are toxins from other genera as well as the link to neurodevelopmental disorders and to mast cell activation. Ochratoxin A is not in the foreground there.

I therefore cite the work only as general evidence that mycotoxins are discussed neuropsychiatrically at all. The step from there to a concrete mental fog with OTA is my own interpretation and not a study result.

Ratnaseelan AM, Tsilioni I, Theoharides TC. Effects of Mycotoxins on Neuropsychiatric Symptoms and Immune Processes. Clin Ther. 2018;40(6):903-917. doi:10.1016/j.clinthera.2018.05.004 [In vitro, In vivo, Review article]

Before you attribute the fog to mould

Mental fog, word-finding difficulties and lack of drive are unspecific. It would be dishonest to offer you a toxin explanation here and keep quiet about the common causes.

What belongs in a work-up first: an underactive thyroid, a vitamin B12 deficiency, an iron deficiency, anaemia, obstructive sleep apnoea, depression, medication side effects and, depending on age and course, an early cognitive disorder. Much of that is treatable. Only after that is the additional look at the living situation worthwhile.

From this the bridge described in the Pillar becomes understandable: OTA does not attack one organ, but several in parallel. Kidney and brain are two sides of the same coin, because the same cellular damage mechanism can act in different places.

Why Ochratoxin A stays so long

This is, for me, the truly decisive point that many underestimate. OTA is not only toxic, it is tough. It does not disappear overnight.

Two properties can explain this. First, OTA binds very firmly to albumin, the most common protein in the blood. As long as OTA is bound to albumin, the kidney can excrete it only with difficulty. It circulates along. Second, OTA undergoes an enterohepatic circulation. This means: what the liver releases into the gut via the bile can apparently be reabsorbed there to a considerable extent, instead of being excreted. A revolving door instead of an exit door. This description comes predominantly from cell and animal models, in humans it has not been measured directly at every step.

The core in one sentence

The plasma half-life of OTA in humans was calculated as around 35 days in a toxicokinetic investigation in one single volunteer. That is a very narrow evidence base, expressly a single case. It does fit what is known about the firm albumin binding and the enterohepatic circulation. What can be derived from it is that OTA probably stays in the body for weeks rather than hours and that a past exposure can remain detectable for longer.

Studer-Rohr I, Schlatter J, Dietrich DR. Kinetic parameters and intraindividual fluctuations of ochratoxin A plasma levels in humans. Arch Toxicol. 2000;74(9):499-510. doi:10.1007/s002040000157 [Case, human kinetics, single person, n=1]

This long residence time is also the reason why, with OTA in particular, the sequence of therapy is so important. Whoever wants to interrupt the enterohepatic circulation relies, among other things, on binders in the gut. This is the mechanistic background to why these substances play a role in mould therapy, always under medical supervision and never as a self-experiment. More on this in the Leaky Gut spoke and in the detoxification part of the Pillar.

The three most important OTA producers in brief portrait

So that you understand where your OTA might come from, here are the fungi behind the toxin. It is worth keeping in mind the difference between food and indoor sources.

Aspergillus ochraceus

The eponymous producer

The most important known OTA producer. Found in foods such as coffee, wine and dried fruit and in indoor environments with prolonged dampness. In the body, OTA concentrations can build up over weeks.

Significance: classic source of food and indoor exposure.

Penicillium verrucosum

The grain specialist in cool climates

In temperate climate zones such as Central Europe the central OTA former on stored grain. Grows even at lower temperatures when storage is damp. This makes it an important factor for exposure through bread and grain products.

Significance: main source of grain-related OTA load in Europe.

Aspergillus niger

The supposed black mould

Common in bathrooms and on damp walls, often confused with Stachybotrys. According to the available investigations only a part of the strains forms OTA. Detecting the species alone therefore says little about whether toxin is actually being formed. Relevant above all with indoor dampness.

Significance: frequent indoor co-occupant with variable OTA potential.

If you want to go deeper into the genus: you will find the overview of all relevant species in the Aspergillus spoke.

The PNEI lenses on Ochratoxin A

In Clinical Psychoneuroimmunology we do not look at a single symptom, but at the systems that together fall out of rhythm. With OTA several lenses interlock.

Nervous system

OTA can cross the blood-brain barrier and burden nerve cells via oxidative stress. Brain fog, word-finding difficulties and lack of drive are the clinical accounts that fit.

Metabolism and kidney

The kidney as filter carries the main load. At the same time OTA can weaken the mitochondria, that is the energy centres of the cells. This connects kidney burden and chronic exhaustion mechanistically.

Immune system

OTA can act immunomodulatingly in models. A persistently irritated or simultaneously exhausted immune system is a recurring pattern in chronic mycotoxin load.

Detox and liver

The liver conjugates OTA and shifts it into the gut. Through the enterohepatic circulation it comes back. Glutathione is a central player here and its reserve can fall under continuous load.

How Ochratoxin A exposure can be detected

There is no single test that proves OTA exposure. Diagnostics with OTA is detective work from several building blocks. The overall picture counts, not a single value.

History of the living situation: water damage, damp basements and bathrooms, onset of symptoms in connection with a move. Better at home or on holiday?
Dietary history: a lot of coffee, a lot of grain, dried fruit, wine, the way supplies are stored.
OTA in urine or blood: measurable in specialised laboratories, best embedded in a complete mycotoxin profile. A single measured value is only one piece of the mosaic. That this measurement is professionally contested I say openly directly below this list.
Basic laboratory tests: kidney values and inflammation markers for context, even if they are non-specific.
Building biology investigation: indoor air and material analysis where there is reasonable suspicion of an indoor source.

Important context, including against my own position

Mycotoxin values in the urine are not standardised like a blood count at the family doctor. Different laboratories measure differently, and the values fluctuate. A single OTA value is neither an acquittal nor a proof.

Honesty requires naming the counter-position, and not in the small print. A review article from allergology and immunology concludes that a so-called toxic mould syndrome is not established, and expressly describes procedures such as measuring mycotoxins in urine or testing homes for spores as not validated and without relevance to a clinical disease. That position is part of the professional discussion, and I do not hold it back here.

I therefore use the value not as proof, but only as one piece of the mosaic alongside the history and the living situation, and I do not recommend it as a routine test for everyone. The costs are as a rule borne by the patient.

Chang C, Gershwin ME. The Myth of Mycotoxins and Mold Injury. Clin Rev Allergy Immunol. 2019;57(3):449-455. doi:10.1007/s12016-019-08767-4 [Review article, counter-position]

How you can reduce the exposure

Now the part that gives you back the ability to act. With OTA the same logic applies as in the whole cluster: first the source, then the body. And everything that goes beyond simple lifestyle measures belongs in medical supervision.

Level 1, foundation

Reduce the sources

Indoors: keep humidity below 60 percent, ventilate the bathroom after showering, remediate water damage promptly and professionally instead of painting over it. Food: buy coffee, grains and dried fruit in tested quality, store dry and cool, dispose of visibly mouldy food completely.

Level 2, stabilise

Prepare the body

Regular bowel movements, sufficient fluids, stable sleep, anti-inflammatory diet. This unassuming foundation determines whether the excretion pathways are robust enough at all before one goes further.

Level 3, targeted support

Medically supervised building blocks

Binders can interrupt the enterohepatic circulation of OTA in the gut. Colestyramine, which is discussed most often here, is prescription-only. Its use for mycotoxin binding is off-label, that is outside the marketing authorisation, with a separate duty to inform and document and as a rule without reimbursement.

Important to know: binders do not bind only toxins. They can markedly reduce the uptake of other medicines, for example thyroid hormone, anticoagulants, digoxin, antiepileptics and the contraceptive pill. They can deplete fat-soluble vitamins and cause constipation up to bowel obstruction. With a complete obstruction of the bile ducts they must not be given. The same applies analogously to over-the-counter binders such as activated charcoal, zeolite or chlorella. This therefore belongs in medical hands and never in self-experiment, and the timing interval to your other medicines has to be set medically. I deliberately say nothing about dosages here.

Whether anything beyond that makes sense for the liver, glutathione metabolism or gut lining depends on the findings and on the examination. I deliberately name no preparations and no promises of effect for that here.

Reframe

You are not helplessly at the mercy of the exposure. The biggest lever is the source, not the next dietary supplement. A dry home and consciously stored food often do more than any expensive powder. The rest is fine-tuning with a medical hand.

Who needs particular caution

In pregnancy and breastfeeding, binders and any attempt at elimination should not be touched without a medical assessment. OTA can cross the placenta and is detectable in breast milk. Precisely for that reason the focus here is on reducing the source and not on trying to pull something out of the body.

In children and adolescents the intake per kilogram of body weight through grain products is highest. Concepts from adult medicine cannot simply be transferred, that belongs in paediatric hands.

If you have a known kidney disease or a liver disease, please do not undertake self-experiments and coordinate every measure with the practice treating you.

And quite generally: do not stop any medically prescribed therapy and do not postpone any planned work-up because of this article. With acute symptoms such as a suddenly sharp drop in urine output, breathlessness, confusion or severe pain, please call the emergency number 112 and do not wait for an appointment.

Coffee, wine and bread: do I have to be afraid now?

No. And that matters to me. This article is meant to give you orientation, not to spoil the enjoyment. OTA is widespread. That is why authorities set maximum levels for food and monitor them.

Honesty requires the other half. The European Food Safety Authority EFSA concludes in its 2020 assessment that the margins of exposure for the neoplastic endpoint are not comfortable in almost all exposure scenarios, and that for high consumers in younger age groups there is a possible health concern for the non-neoplastic endpoint as well. At the same time EFSA states a high uncertainty in its own assessment and holds it possible that the risk is overestimated. What I make of that: no reason for panic, but no reason to wave the topic away either. The dose over time is the lever you can really move.

OTA becomes relevant when several factors come together: a high continuous dose through food, an additional silent indoor source and a body whose excretion is overloaded for other reasons. Those who are sensitive or have known mould exposure gain the most by addressing both sides at the same time: the home and the pantry.

Official document Review article Mould and indoor environment

The World Health Organization summarises in 2009 the evidence on dampness and mould in indoor environments. Damp, mould-affected buildings are associated with increased health risks, above all for the airways.

Important for context: the WHO expressly does not attribute these effects to individual mould species or to individual mycotoxins. For Ochratoxin A specifically, nothing can be derived from this report. What it does support very clearly is the practical consequence: moisture in a building is a health topic in its own right and belongs remedied.

WHO. Guidelines for indoor air quality: dampness and mould. 2009. WHO official document [Authority Document, Review article]

Frequently asked questions about Ochratoxin A

What is Ochratoxin A?

Ochratoxin A, OTA for short, is a mycotoxin produced mainly by moulds of the genera Aspergillus and Penicillium. It is one of the most frequently detected mycotoxins in food. It is also found regularly in damp indoor environments, though there alongside other toxins and in strongly varying amounts. OTA can act nephrotoxically and neurotoxically and was classified by the IARC in Group 2B. Group 2B means that the evidence for a carcinogenic effect in humans is not sufficient to establish it, and not that OTA causes cancer in humans. I expressly do not offer cancer screening, cancer prevention or cancer treatment in this context.

Where does Ochratoxin A occur?

The main dietary sources are grains and grain products, coffee, wine and grape juice, dried fruit, spices and cocoa. Indoors, OTA forms with prolonged dampness and after water damage, when Aspergillus and Penicillium species grow on building materials. Uptake occurs through food, the airways and partly through the skin.

Why does Ochratoxin A particularly affect the kidney?

The kidney can accumulate OTA because, on current understanding, the toxin can be taken up into the cells of the kidney tubules via transport systems. There it can trigger oxidative stress, mitochondrial damage and cell death in cell and animal models. OTA is therefore counted among the mycotoxins with a particular kidney emphasis. Human data are limited, the mechanistic evidence from cell and animal models is consistent. Important on sequence: abnormal kidney values have far more common causes, for example diabetes, high blood pressure, inflammation of the renal corpuscles, regular use of painkillers or an obstruction to urine flow. Those belong in a general practice or nephrology work-up first.

Can Ochratoxin A affect the brain?

In animal models OTA can cross the blood-brain barrier and accumulate in brain regions. Described are oxidative stress, neuroinflammation and a loss of nerve cells. In review articles OTA is associated with cognitive slowing and neuropsychiatric symptoms. In humans this link is not conclusively proven. Concentration problems, word-finding difficulties and lack of drive also have far more common and often treatable causes, for example an underactive thyroid, vitamin B12 or iron deficiency, anaemia, sleep apnoea, depression, medication side effects or an early cognitive disorder. Those belong in a work-up first.

How long does Ochratoxin A stay in the body?

OTA has an unusually long residence time. It binds strongly to albumin in the blood and undergoes an enterohepatic circulation, in which it is repeatedly reabsorbed. The plasma half-life in humans was calculated as around 35 days in a toxicokinetic investigation in one single volunteer. That is a very narrow evidence base, but it fits what is known about the firm albumin binding and the enterohepatic circulation. What can be derived from it is that OTA probably stays in the body for weeks rather than hours and that a past exposure can remain detectable for longer.

How is Ochratoxin A exposure detected?

One option is measuring OTA in urine or blood in specialised laboratories, embedded in a mycotoxin profile. I say openly that this measurement is professionally contested. Review articles from allergology and immunology consider mycotoxin measurements in urine insufficiently validated and see in them no proof of a disease. Also important are the history of living and dietary habits and, where appropriate, a building biology investigation. No single method is conclusive, the overall picture counts, and the costs are as a rule borne by the patient.

How can I reduce Ochratoxin A exposure?

First comes reducing the sources: a dry living environment, professional remediation of water damage, conscious choice and storage of coffee, grains and dried fruit. Everything beyond that I plan individually and in a fixed sequence. It can include prescription-only medicines and, depending on the situation, accompanying measures for diet and gut health. I deliberately name no preparations and no promises of effect here, because that would not be sound without findings and without an examination. In pregnancy and breastfeeding and in children, every such step belongs in a medical assessment first.

Is coffee dangerous because of this?

Coffee is a relevant OTA source, but no reason to panic. The exposure varies greatly depending on cultivation, processing and storage. Those who are sensitive or have known mould exposure can pay attention to tested quality, fresh roasting and dry storage. A general demonisation of coffee is, in my view, not appropriate.