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Should I Use a DAO Supplement? (Diamine Oxidase)

DAO (Diamine Oxidase) supplements are being used increasingly often by people afflicted with chronically high histamine levels. It’s become one of the most popular histamine intolerance supplements, in part because it’s now being used as a sort of home test for histamine intolerance— if it lessens your symptoms, you’re on the right track.

Symptoms of histamine intolerance (chronically high histamine levels) include migraine headaches, recurrent headaches, nasal congestion, gastrointestinal problems, sneezing, shortness of breath, cardiac arrhythmias (heart rhythm abnormalities), hypotension (low blood pressure), anxiety, and flushing and itching of the skin.

The rest of this article is focused upon what DAO is, how to increase DAO naturally, and how to find the best DAO supplement or DAO-boosting activities for your needs.

Medical Disclaimer: as with everything on this site, this article is provided for information only. I strongly urge you to speak with your doctor or a licensed medical professional in order to assess whether or not you should incorporate a DAO enzyme supplement into your regimen.

Nuts are a great source of copper and iron, two of the five cofactors required for your body to produce DAO.

What is the DAO Enzyme?

DAO is an enzyme essential for histamine degradation; it’s normally produced in the kidneys, the lining of the intestines, and the thymus. Enzymes are a type of protein molecule which catalyze or accelerate the speed of chemical reactions in the body, while chemicals known as co-factors assist these enzymes in the execution of such reactions.

The co-factors vitamin B6, vitamin C, and copper are essential for the production and proper functioning of DAO. The enzyme’s main function is to metabolize (digest) and cause the breakdown of excess amounts of histamine in the body, whether ingested or produced internally.

This breakdown results in a vast reduction of histamine intolerance symptoms, and generally within a half hour. It also works in conjunction with another enzyme known as histamine methyl transferase (HNMT) to reduce the levels of two toxic byproducts of histamine breakdown called N-methyl histamine and imidazole acetaldehyde.

DAO supplements have quickly become one of the most commonly-used supplements to treat a histamine reaction, especially when caused by dietary histamine.

A snapshot of some of the supplements & medications I was taking my first few months eating low histamine.

DAO & Histamine Intolerance

As you’ll quickly learn, “intolerance” isn’t the most accurate description of what’s going on inside the body of someone with histamine intolerance. The better term would be “histamine overload” or “histamine toxicity,” as the symptoms of the illness are due to the overabundance of histamine in the body.

But to backtrack a bit, why does this overabundance of histamine cause symptoms which mimic a food allergy or food intolerance? The connection lies in the immune system.

Histamine is a nitrogen-containing biogenic amine found in most tissues of the body. This means that it’s not only very important to the functioning of most bodily systems, but it can also have a huge effect on them.

Molecules of histamine are produced and stored in histamine-containing granules that are found in mast cells as well as in a type of blood cell called basophils, both of which are integral parts of the immune system.

Histamine release is stimulated as an important part of the body’s inflammatory response to allergens, such as certain foods, pollen, insect bites, various drugs, and dust. The effect of histamine release is incredibly similar to the symptoms typical of an allergic response, in addition to anxiety, dysautonomia, and even mood swings.

Reactions can occur in response to endogenous histamine (produced) or to exogenous histamine (consumed), but high histamine food is the number one reported trigger. Being able to clear histamine from the digestive tract is a major tool in your arsenal, and that’s where DAO comes in.

Basil is a great antihistamine herb to work into your regular meals, lessening your need for DAO supplements.

What is DAO Deficiency?

DAO deficiency occurs when the body’s levels of diamine oxidase have dropped low enough that your body is unable to eliminate unnecessary histamine, resulting in buildup.

Once DAO deficiency occurs, your body’s histamine level will naturally continue to rise, leading to all the physical symptoms of excess histamine referenced above. Causes of DAO deficiency include:

  • Excess alcohol consumption
  • Overgrowth of the bacteria normally found in the intestines (SIBO) or Leaky Gut Syndrome
  • Consuming large amounts of high histamine foods
  • Genetic mutations which impair your body’s ability to make DAO or make use of its cofactors
  • Hormonal imbalances
  • Certain types of medications which function as DAO blockers (including drugs such as chloroquine, isoniazid, and verapamil)
  • Chronic gastrointestinal disorders such as Irritable Bowel Syndrome (IBS), Crohn’s disease, or Ulcerative Colitis
  • Heavy metal poisoning (such as copper toxicity or lead poisoning)

Some of these causes of low DAO can take decades to build up and express themselves. For example, DAO deficiency can be due to genetic polymorphisms that reduce the normal activity of DAO, or even by a reduction in the available amounts of the cofactors needed for DAO production.

As you get older, DAO production decreases, so any minor genetic mutations may increase in effect as you age. DAO deficiency is usually treated with DAO supplements, but it’s also important to make sure you consume a balanced diet, so that you’re healthy enough to produce enough DAO on your own.

Major side effects of DAO supplements are rare, but they have occurred, mainly in people with autoimmune and inflammatory diseases. So always talk to your doctor before starting a new regimen or changing your existing one.

Possible side effects of DAO consist of nausea, headache, lethargy, hives, and symptoms similar to those of the flu— so basically the same as those of histamine intolerance.

Pea sprouts, another great— but fleeting— source of DAO

Best DAO Supplements

DAO supplements are more widely available than ever, but they should not be your first defense against histamine. Their purpose is just to temporarily enhance the level of DAO enzyme in the body, in order to better metabolize high histamine foods and reduce the symptoms of histamine intolerance.

If taking a “magic pill” were all that’s needed to clear everyone’s histamine symptoms, we wouldn’t even be here. So before diving into DAO supplementation, I want to once again state that I am not a medical professional and that you should always speak with your doctor before trying something like DAO.

That said, once you’ve done an elimination diet and ruled out other possibilities, like gluten intolerance or an allergic reaction, then you should consider DAO supplements. Every brand will contain varying concentrations, but they’re widely available over-the-counter.

Even high doses don’t require a prescription. One study has indicated that a helpful dose of supplementary DAO is roughly 4.2 mg, taken ideally right before meals.

One more popular histamine intolerance supplement with this amount of DAO is Seeking Health Histamine Block, which I’ve never used, but is apparently very effective. I personally prefer to consume whole foods when possible, even in supplements, which is why I started with and continue to use Ancestral Supplements’ Bovine Kidney.

The DAO content in whole kidney will vary a bit by brand. But I’ve found it to be the best DAO supplement for histamine intolerance, helping ease my reactions even more than stinging nettle or quercetin have.

This may be because all the best DAO supplements contain some amount of kidney, usually derived from grass-fed cattle that have been allowed to graze freely. Pea sprouts are another great source of DAO, but they must be consumed fresh for the DAO to be used by the body.

One great way to do this is by adding them to your next smoothie. I’ve learned from experience that taking your source of DAO approximately ten to fifteen minutes before consuming a high histamine meal can help metabolize histamine from any food or drink source.

Though this only helps if DAO deficiency is to blame for your histamine sensitivity. For those who have a type of mastocytosis or a mast cell activation disorder (MCAD), additional DAO may not help unless you figure out your non-food triggers, as well.

Ancestral Supplements Bovine Kidney

The best DAO supplements for histamine intolerance will have been thoroughly tested for heavy metals and potential contaminants, with all levels well within the range safe for human consumption. They should also be fully tested by a third party laboratory.

Most companies will have results posted on their website, and should not contain any unnecessary fillers. A high quality diamine oxidase supplement will also be free of any GMOs, and formulated based on the latest scientific research.

Histamine blocking supplements often contain vitamin C, which helps to normalize the level of DAO long-term, and aids in the normal breakdown of histamine. In addition, histamine intolerance is often due to problems with the normal bacterial flora of the gut.

So many of the top DAO supplements also contain probiotics, which help to restore intestinal balance. Regardless, studies have found that DAO supplementation by itself does help in the improvement of symptoms of patients who have histamine intolerance, so find what works for you.

How to Increase DAO Enzymes (Naturally)

Now that we’ve looked at supplements, let’s look at how to boost DAO levels without adding more pills to your day. There are a number of different ways to increase DAO enzymes naturally, which you can do in place of or in addition to DAO supplements.

You should begin by starting a low histamine diet. To start eating low histamine, first you must eliminate foods that are known to be high in histamine, such as fermented foods and drinks. You can also increase your DAO enzymes naturally by carefully balancing your low histamine diet.

Consider asking your doctor to run a blood test to check your levels of copper, iron, vitamins B6 & B12, and vitamin c (ascorbic acid), especially if they’re not familiar with histamine intolerance.

All of these nutrients are necessary for the proper breakdown of histamine by DAO, so make sure they’re present in your regular diet and that if you have a deficiency, it gets addressed. It’s also important to balance the different types of protein and fat you’re intaking.

This means decreasing your intake of Omega-6 fatty acids, such as those contained in highly processed foods, and increasing your intake of healthier fats, like Omega-3 and Omega-9 fatty acids. An often-cited study into rats found that oleic acid in particular— an Omega-9 fatty acid found in olive oil— increases the amount of DAO secreted into the blood stream.

Changing the types of protein you’re eating can also naturally increase the amount of DAO released by the gut. Particularly eating organic plant proteins and grass-fed meats can help to naturally increase DAO levels in the body.

Avoiding additives, artificial preservatives, and pesticide-laden foods has also been found to increase DAO. Though it’s more likely that those substances themselves are DAO blockers, artificially inflating histamine levels.

Finally, lowering your overall stress has been found to naturally increase DAO, most likely by reducing systemic inflammation and decreasing demand for DAO.

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A. Walker

Monday 24th of April 2023

All DAO in the U.S. comes from the same distributor.


Monday 24th of April 2023

That may somehow be true, but being distributed through the same sources doesn't mean that they're made from the same materials. Some come from pig & some come from bovine sources, and they're all made in various different places.


Friday 31st of March 2023

I have MCAS. I am having a blood test to determine my DAO level. If a supplement worked would I need to take it for life?


Sunday 2nd of April 2023

No, if a supplement worked indefinitely, it would mean you had chronically high histamine levels and that your doctor wasn't getting at the root of your issues. Because DAO only addresses high histamine in the meal that you're eating; it wouldn't help you with histamine release due to MCAS reactions.

If you have MCAS, you should determine which foods and environments trigger you & avoid them to the best of your ability, as well as work with your doctor to find a daily antihistamine and maybe mast cell-stabilizing medicine regimen that would help support your natural DAO pathways and get the MCAS symptoms under control. does a better job at explaining the difference between taking DAO & making your own in some of her resources, but I'll have to work on a post addressing that. Thank you for your question, Kevin!

Mandy Parker

Saturday 24th of December 2022

Thank you for your help 🙏🏻 This is a whole year now since my first attack it was the most horrendous experience ever in my life which resulted me whisked off to a&e with suspected stroke thankfully it wasn’t but was anaphylaxis caused by food intolerance and I have been on elimination diet since and diagnosed Vestibular Migraine brought on by foods I cope well whilst at home with my own cooking but eating out is huge problem I take vitamins C, D, E, Iron, Iodine, Antihistamine all work well without any problems and a Sumatriptan for when I feel an attack starting usually after eating something when dining out. But now I want to start taking a DAO supplement your article is the first most helpful and understanding of this miserable debilitating disease I have read and gives me hope that the supplements you recommend will help me more in my long journey of food intolerance recovery Thank you so much #grateful #hopeful


Tuesday 7th of March 2023

@Mandy Parker, Hugs to you Mandy! Sorry to hear of your scare.

Mark A

Tuesday 28th of February 2023

@Mandy Parker, I had the same symptoms for nearly 20 years……yes, 20! Have a naturopath order a Mycotox panel from Great Plains Lab and also order a Marcons nasal swab test. If you can afford it ….please do it! Don’t suffer like I did for so long. Hope this helps.


Saturday 24th of December 2022

That sounds like a horrifying experience! I'm so sorry you've been dealing with that, Mandy, and I'm glad that at least at home you've gotten a handle on what your triggers are. Being 'out in the world' is always hard, because it turns out most people don't know what's in the food they're serving-- scary, right? But I try to think on the bright side of things, and choose to see it like my body making me pay closer attention to what I put in my body, and hopefully enjoy it more. I hope you get even more of a handle on it soon, and I'm glad to try to connect you with any of the knowledge you need on the subject!


Saturday 3rd of December 2022

The kidney supplements gave me palpitations. :( I was using the One Earth Health brand.


Wednesday 22nd of February 2023

@Max, Can you recommend a plant based DAO supplement? I am allergic to beef. It will even cause a flare in my eczema.


Thursday 8th of December 2022

@Max, Now I'm learning that some people need to freeze the capsules. 🤔


Wednesday 7th of December 2022

@Max, Maybe it's the gelatin capsules?


Sunday 4th of December 2022

That may be a histamine reaction; you may need to take a plant-based DAO, or add pea sprouts into your meals. There are alternatives, but I'm sorry you're having heart palpitations with the kidney form. :/


Saturday 18th of June 2022

Your article is a great help for me to find a temporarily solution for my severe HIT I recently figured out that I have been suffering from my whole life. I wonder you have ever had constipation and dry mouth after taking DAO supplement?

Mark A

Tuesday 28th of February 2023

@Holly, I had the same symptoms for nearly 20 years……yes, 20! Have a naturopath order a Mycotox panel from Great Plains Lab and also order a Marcons nasal swab test. If you can afford it ….please do it! Don’t suffer like I did for so long. Hope this helps.


Saturday 18th of June 2022

@lowhistamineeats, Thank you for your reply and it is a great relief as well. I am grateful I can connect with someone out there in the world finally. I had a severe vertigo in late February and went to ER. No doctors knew what had happen to me. I went to see countless doctors for my vertigo and dizziness which I had every day and have been treated as stroke in my brain, Meniere disease and food poisoning (I can’t eat nuts, eggs, even meats anymore that contains high proteins which make my symptoms worse). In my country, no one ever heard of histamine intolerance. When I feel like I am dying, I came across your article. What a bless! Can I ask you if you take Vitamin 6 and Zinc? If so, what brand are you taking and dosage you are using?


Saturday 18th of June 2022

I'm sorry you've been suffering, but I'm glad to help provide some relief! I'm never had constipation or dry mouth after DAO, but the histamine-induced inflammation does seem to sometimes cause me to alternate between diarrhea and constipation in times of great stress, so it's possible your situation is unrelated to the DAO.

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