Diamine Oxidase Enzyme (DAO)

Low DAO may lead to increased blood histamine levels.

DAO is an enzyme found in the blood and the digestive system.

LocationWhat does it do?Consequence of reduced activity
Digestive SystemBreaks down histamine in the digestive system (from food or that is released).The excess digestive histamine will enter the blood stream.
BloodBreaks down histamine circulating in the blood.Histamine is not broken down, so it continues to build-up (see below).

Normal Diamine Oxidase Enzyme maintains blood histamine levels


Reduced Diamine Oxidase Enzyme may allow histamine to increase in the blood


Many factors have been suggested to reduce DAO activity. However, there is no research to support these claims.

The potential factors to reduce DAO activity include:

  • Genetics: some people may be genetically programmed to produce less DAO enzyme.
  • Intestinal damage: Damage or inflammation to the inner lining of the digestive system may decrease DAO (digestive DAO is in the lining).  However, if this were true, people with undiagnosed celiac disease (which causes significant inflammation in the digestive system) would experience histamine related symptoms. However, these symptoms are no more common in undiagnosed celiac disease than the general population. This theory still makes sense and may occasionally account for low DAO, but is not a given fact.
  • Potential DAO blocking factors, including:
    • Certain medication: There are long lists of “DAO blocking” medications on the internet. Similar to problematic dietary lists, the medication lists are primarily based on anecdotal reports (i.e., people assume that problematic medications are DAO blockers). However, there has only been one research study that has investigated this topic. The study demonstrated that some medications inhibit DAO in a test tube.  Further studies are needed to see how this applies to real life situations. Also, only a handful of medications were studied. The effect of other medications is not known. The right medication can be more important than potential DAO inhibition. For example, one client attributed his symptoms to an antibiotic that he received in the hospital. However, that was the best antibiotic to cure his infection. Without it, he may have died.
    • Alcohol: Most clients report significantly worse symptoms with alcohol intake. There is no direct evidence, but alcohol is thought to inhibit diamine oxidase.
    • Foods with elevated diamine content:  Histamine is the focus, but many other diamines form in food alongside histamine (see Related Diamine Compounds in Histamine in Food). The other diamines are also broken down by diamine oxidase enzyme (DAO) – reducing histamine breakdown.
    • High body histamine level: Chronic histamine excess in the body (e.g., allergies, stress, mast cell disease, etc.) may reduce DAO production. Lowering body histamine may increase DAO production, which possibly explains why some clients find benefit from a low histamine diet, but can gradually return to their usual diet after about four weeks.

There are no validated tests for diamine oxidase status.

Tests that measure the activity of DAO in the blood are available in Europe (to my knowledge there are no labs outside of Europe that offer this test). The results from the few research studies are interesting but are not enough to establish it as a validated test. Additionally, it is unknown if blood DAO activity correlates with digestive levels (and digestive levels is the foundation of the histamine intolerance theory). In the United States, some labs offer DAO testing, but this is a different technique than the European tests, and there is no research to support them.

Diamine oxidase enzyme supplements are available in tablet form.

This supplement helps break down histamine in the digestive system, reducing absorption into the blood stream.


DAO supplementation has been shown to improve histamine associated symptoms in a few clinical trials, but more research is needed. It is difficult to predict which clients will benefit, so the best thing is to try it (without making any other treatment changes).


Take the DAO supplement about 15 minutes before a meal. The capsule needs time to breakdown in the stomach so the enzyme can mix with the food. Finish your meal within 15 minutes (and don’t snack afterwards!) The number of tablets depends on several factors and everyone is different. It takes some experimentation.


Sciotec (an Austrian company) produces the diamine oxidase supplement and sells it under different brand names throughout the world.

Europe: The brand name is DAOsin.

Canada/United States: Several brands that were previously available in the United States have been discontinued. Diamine oxidase will be distributed directly by a Sciotec JV partner under the brand name Umbrellux DAO  with the typical 10,000 HDU per capsule. Other supplements that either feature DAO in the product name or claim to contain DAO but don’t show any HDU are misleading consumers.

20 comments on “Diamine Oxidase Enzyme (DAO)
  1. Liz says:

    Hi Wendy,

    I have recently been diagnosed with a likely histamine intolerance. I plan to follow your guidelines on reducing histamines. But I would also like to test the effectiveness of supplementing with DAO. As per your instructions above, do you suggest testing the supplements by eating regular/high-histamine foods with the supplements before you make any other diet modifications?

    Thank you,

    • Wendy says:

      That’s a great question, Liz! There isn’t an exact right way to try the DAO supplement. Here’s one approach:

      • Try DAO for 2 – 3 days on your unrestricted diet (with each meal).
      • Then try the lower histamine diet as described in the Practical Guide (without DAO).
      • If the diet has helped and you have a better understanding of which foods are most problematic, see if the DAO supplement helps you tolerate these foods.

      Keep a journal of what you discover at each step. It is easy to forget.

  2. Martha says:

    Hi Wendy,
    Thank you for your content and website. Very helpful. HisDAO is a supplement I’ve recently used from Xymogen. I was also recently tested in US from Dunwoody Labs. Have you heard of their Advanced Intestinal Barrier Assessment test? This test will measure DAO and Histamine levels..plus more. Interested in your feedback. Thank you. Martha

    • Wendy says:

      Similar to many of the tests available, this test is based on science, but the usefulness has never been researched. Blood DAO, histamine, zonulin are important in health. There are a few studies with DAO and histamine, but a lot with zonulin. However, before I would recommend a test, I would like to see studies that take it from theory to clinical relevance.
      The important “test” is if you notice a substantial improvement with the DAO supplement.

  3. Catherine Michealson says:

    I’ve been diagnosed recently with indalent Systemic Mastocytosis. Is burning mouth a symptom. Chewing gum is the only thing that helps
    Where can I get a copy of your diet

    • Wendy says:

      With so many symptoms associated with mast cell disease, it is hard to say what is and what is not a symptom. Mouth Burning Syndrome is probably more common in mast cell disease than the general population, but that does not mean that it can be directly attributed to the disease. Your specialist would be the best person to talk with about this.

      Wendy’s Low Histamine Diet Guidelines can be found on the Practical Guide to the Low Histamine Diet. The low histamine diet is an “educated guess,” based on client reports. There are several variations of this diet on the internet and there isn’t a “correct diet.” The best diet is very individual.

  4. Elke Puglak says:

    Is anyone else getting migraines or headaches from Umbrellux Dao? It helps most of the other histamine symptoms but gives me a nasty migraine or headache every time I take it. I have never eaten pork, but was getting desperate. I am down to eating the same 10 foods each day. Am considering sprouting peas. Anyone had relief with the pea shoots? I have been on a low histamine, low oxalate, low tyramine diet for 18 months.

    • Wendy says:

      Hi Elke- I apologize for the late response. It’s been a busy week! I have not had that many people report that sprouted peas improved their symptoms. However, sprouts are nutritious. If you have the time, it is worth trying. My specialty is helping people expand their diet, so please let me know if you need assistance. You can find further details at:

  5. RG says:

    What about Hist-DAO?
    My Functional Medicine Medical Doctor here in Canada has just recommended this product to me.
    I would like to do more research before taking it though.

    Thank you,

  6. Bonnie says:

    are there any DAO supplements without PORK?

    • Wendy says:

      Hi Bonnie – DAO is made by one company (Sciotec) and it is derived pork kidney. DAO is available under many different brand names, but they all have the same DAO. Peas sprouts may possibly be a source of DAO. Sprouts have many other nutrients as well. Even if they don’t help your symptoms, they will give you a nutrient boost (hopefully, you tolerate them). Here’s an article: http://www.low-histamine.com/tag/pea-sprouts/

      • Dama says:

        Dear Wendy,

        There are other supplements with greater DAO enzymatic activity, such as DAOfood (recommended when the predominant symptoms are digestive) or Migrasin (recommended when the predominant symptom is migraine). These products are presented in tablets or mini-tablets with gastric protection.

  7. Bonnie says:

    please help me find a DAO supplement without pork.

  8. Greg Speagle says:

    I there a supplier for Umbrellux DAO in Canada?

  9. Greg Speagle says:

    Is there a Supplier in Canada for Umbrellux DAO

  10. June Tucker says:

    Very interesting explanation regarding DAO. I have a major problem with histamine intolerance. I have been on a low histamine diet for over 9 months but continue to have problems when re-introducing foods. Diet is very limiting, especially so when I have osteoporosis. My nutritionist doesn’t support my suggestion of trying a DAO supplement, wanting me to continue taking probiotic. This problem does make for a very miserable existence, especially when things flare up badly.

    • Wendy says:

      I feel that health care professionals should be supporting their clients on the journey, rather than directing it. I would encourage you to try the diamine oxidase supplement, but making only that one change (so you know if it is helping). The good news is hat you will know quickly (see article). My speciality is helping clients reintroduce foods, so my services would be a good fit for you.

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