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  • Writer's pictureNicola Hodges Nutrition

Histamine intolerance may play a part in chronic conditions including long covid & gut issues.

A bit of background. What is histamine?

We are all familiar with histamine when it comes to chronic allergies like hay fever and severe food allergies that require medical attention. Histamine however is so much more than just a key player in these conditions.

Histamine is also an excitatory neurotransmitter involved in wakefulness, goal-orientated behaviors, and both short and long-term memory. Interestingly histamine also plays a part in feeding behavior and satiety and is involved in gastric acid secretion and blood clotting.

Histamine can also come directly from the food we eat. Histamine poisoning was first described more than 60 years ago, the ill effects of excessive histamine ingestion were initially referred to as scombroid fish poisoning- decaying sea animals have very large amounts of histamine. There is food safety legislation in place in the EU limiting the amount of histamine that is permitted in fish but not in other foods.

The consumption of low amounts of histamines in food does not usually cause problems. I'm suggesting that maybe modern living has impaired our ability to handle higher amounts of histamine. This could be due to increased availability and consumption of other high-histamine foods and drinks, impaired gut health (due to unbalanced gut bacteria caused by various factors including a typical high sugar western diet), impaired liver health, increased incidence of autoimmune disease, oestrogen dominance (more on that in a moment), increased chronic stress levels, medications and increased exposure to environmental chemicals.

"The often undiscussed issue is that histamine intolerance and or mast cell activation syndrome (MCAS) may be involved in many common chronic diseases and conditions such as Long covid, ADHD, constipation/loose stools & PoTs"

Histamine is released from cells called 'mast cells' (and white blood cells called basophils) in response to a threat that's entered the body usually via the route of the skin (think insect bite for example), lungs (breathing in pollen), or from food.

Mast cell activation syndrome (MCAS) and histamine intolerance are closely related- the difference being that MCAS results in the release of not only histamine but other inflammatory mediators as well. (Having histamine intolerance does not automatically equate to having MCAS).

The often undiscussed issue is that histamine intolerance and or MCAS may be involved in many common chronic diseases and conditions such as:

-Long Covid


-PoTS (postural tachycardia syndrome)


-Anxiety -Dizziness/vertigo

-Constipation/ loose stools, nausea, vomiting, and abdominal cramping

-IBD (Crohns, coeliac, ulcerative colitis)

-Skin issues such as itching, eczema, and psoriasis

-Fatigue and brain fog


-Sneezing, runny nose/stuffiness, and eyes -Migraine


-Gallbladder issues

-Fainting or nearly fainting (hypotensive syncope)

-Tachycardia (increased heart rate)

•••Always talk to your Doctor first and foremost if you suffer from any of these symptoms•••

Why are some people hypersensitive to histamine and others aren't?

It's important to point out that a robust release of histamine is what our bodies are designed to do in response to a genuine threat invading the body- the problem comes when we make too much for our body to deal with and we lack the capacity to break it down.

We make histamine in our bodies in response to antigens, but as I explained earlier we can eat histamine too! Well actually to be more specific, some foods and drinks have a high histamine content, some foods cause us to liberate our own histamine and some foods block the enzyme we produce to break histamine down.

Examples of high histamine foods are aged meats (well-hung beef), canned, dried, or smoked fish, fish sauce, fermented foods (even healthy ones like sauerkraut and kimchi), alcohol, and mature cheeses. There are many more on the list, this is just an example. Histamine liberators are alcohol, chocolate, citrus fruits, bananas, pears, and peanuts (just a few examples).

"The DAO enzyme is the main enzyme that breaks down histamine"

So why do some people have a dramatic reaction to an insect bite for example where their entire limb swells up and other people simply have a tiny red mark? From a genetic perspective, many of us may have genetic variants on the genes for histamine receptor sensitivity and many of us have genetic variants on the DAO enzyme (DAO is short for diamine oxidase).

The DAO enzyme is the main enzyme that breaks down histamine (along with another enzyme called HNMT - histamine N methyl transferase). We express the DAO enzyme primarily in the gut, but also in the kidneys (and the placenta). Interestingly the DAO enzyme is upregulated by around 500x during pregnancy- it's theorised this is to protect the baby.

I mentioned that some foods/drinks can block the DAO enzyme- these are green and black tea, alcohol (alcohol seems to have the ability to be high in histamine, block DAO, and is a histamine liberator- sorry about that). Some medications are DAO blockers such as NSAID's (among others).

"If we think of histamine as having a histamine bucket that when full up starts to overflow -that is when we get problems"

So we've discussed genetic predispositions but those of you who know me know I often say that we can't blame our genes entirely- that's just lazy! Genetic variants are not our destiny in the way that serious genetic mutations are. This is exactly why it is helpful to test your genetic variants- because we can do things to influence them! I sometimes use a company called Lifecode GX which can run a histamine intolerance report and tests for the genetic variants involved with the various pathways needed to detoxify histamine.

If we think of histamine as having a histamine bucket that when full up starts to overflow- that is when we get problems! We need a healthy gut and a healthy liver in order to detoxify histamine efficiently. We also need a healthy methylation status (methylation is way too complex to go into here, it's a biochemical process involved in DNA production and repair, detoxification and so much more). It's worth knowing that we need a good nutritional status for methylation to work properly such as adequate B vitamins and other key nutrients. We also need to consider that when methylation capacity is drained due to dealing with histamine it can have a knock-on effect on other areas of overall health.

Oestrogen and histamine

Women are at greater risk from histamine intolerance and MCAS due to oestrogen further promoting the release of histamine and in turn histamine promoting the release of oestrogen!

Some women may notice an increase in allergic or histamine-type symptoms at points in their cycle where oestrogen is at its highest.

We also need to remember that oestrogen utilises the same biochemical pathways to detoxify itself from the body as histamine so we can get a 'bottleneck' type situation for both oestrogen and histamine.

What can be done about histamine issues?

Serious histamine intolerance and MCAS is a medical matter that is often discovered quite quickly due to severe the severe symptoms it creates. But when the signs are more subtle or seemingly unrelated and medical issues have been ruled out it may be worth looking deeper into histamine intolerance.

1. A low histamine diet is often a good start. I recommend working with a BANT registered nutritional therapy practitioner for this as the information available can be overwhelming. Please keep in mind that the foods that can cause issues with histamine are not inherently bad and many of them are incredibly nutritious- they should only be avoided if histamine intolerance is strongly suspected and only for a short time whilst working on overall health and resilience.

2. Gut health is key! A leaky gut or an inflamed gut may impact DAO production and increase histamine production (DAO is produced mainly in the gut). Gut infections such as parasites, mycotoxins, IBD, IBS, SIBO, and bacterial dysbiosis (unbalanced gut bacteria) can all lead to histamine intolerance. Histamine intolerance can make gut issues worse and gut issues can make histamine issues worse. In my practice, I often recommend a comprehensive stool analysis test to assess gut health.

3. Look after your liver and metabolic health. Avoid alcohol and excessive sugar.

4. Stress management- there is a link between chronic stress and histamine release.

5. Eat a nutrient dense fresh whole food diet with minimal junk food.

What's the Bottom line

Working with a BANT-registered nutritional therapy practitioner 1-2-1 can be a great support for those suffering from more subtle or suspected histamine intolerance and MCAS. The use of functional testing and the judicious use of nutraceuticals that support the DAO, and HNMT enzymes and also support the detoxification pathways can be incredibly helpful.

The aim should not be to simply avoid high histamine foods for the rest of your life but to improve health and build resilience so that these factors are not nearly so much of an issue.

To learn more about working with me you are welcome to book a free 30 min discovery session via the link below.

Disclaimer: Nutritional therapy is not a substitute for professional medical advice.


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