Wendy Busse, RD

Diamine Oxidase Enzyme (DAO)

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Updated: May 2019

Diamine oxidase breaks histamine down. Reduced activity of this enzyme may lead to symptoms.

Histamine is an important body chemical that circulates through the blood. Diamine oxidase enzyme breaks histamine down and keeps blood histamine in the normal range. Decreased DAO may lead to higher blood histamine levels and possible symptoms. The following video shows how this happens.

Several factors may reduce DAO activity. This information is based on theory and speculation because there has been very little research on this topic.

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. However, patients with undiagnosed celiac disease (significant inflammation in the digestive system) do not suffer with increased histamine related symptoms compared to the general population– which is what you would expect, if this theory were true. Nevertheless, this theory makes sense and may occasionally account for low DAO.

Reduced copper, zinc and B6: These nutrients are co-factors for the DAO enzyme, so theoretically lower levels would reduce its effectiveness. Many practitioners recommend mega-dose amounts of these nutrients, but it’s unlikely to be helpful. For example, if a reduced zinc intake is compromising DAO function, an adequate intake should improve DAO function. However, a mega-dose amount will not increase DAO function beyond an adequate intake. Consider taking a multi-vitamin/mineral supplement, with around 100% of the nutrient requirements.

Certain medication: There are long lists of “DAO blocking” medications on the internet. Similar to the problematic dietary lists, the medication lists are primarily based on anecdotal reports (i.e., people assume that problematic medications are DAO blockers). 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 DAO. 

Foods with elevated diamine content:  As we discussed in Histamine in Food, many other diamines form in food alongside histamine. The other diamines are also broken down by 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.

Tests that measure the activity of DAO in the blood are available in Europe. There have only been a few studies. The results are interesting, but not sufficient to establish it as a validated test. Additionally, it is unknown if blood DAO activity correlates with digestive levels (which is the foundation of the histamine intolerance theory). In North America, some labs offer DAO testing, but it is a different technique than the European tests, and there is no research to support them.

Supplementing the natural DAO in the digestive system may increase histamine breakdown and reduce absorption. However, DAO supplements do not increase blood DAO and therefore, would not reduce histamine from other sources (e.g. pollen allergies).

Pea Sprouts

A few research studies indicate that pea sprouts have high levels of DAO. Dr. Janice Joneja (Immunology Ph.D. and Canadian dietitian) popularized this theory. Very few details are known, so the current guidelines are an educated guess. Hopefully, further research will provide more details (e.g. what legumes, how to sprout them, etc.). However, pea sprouts are nutritious, so it is worth trying even if it does not reduce your symptoms.

Commercial Supplements

Sciotec, an Austrian company, has developed a technique to isolate DAO from pig kidneys. Currently, this is the only commercially available DAO supplement. There have been a few clinical trials, but more research is needed. However, supplements (such as DAO) that make an immediate difference to symptoms require lower levels of evidence than supplements that claim to prevent long -term problems (but the individual has no way to judge its effectiveness).


Sciotec sells the DAO microcrystals under different brand names throughout the world.

The official products in the US and Canada are Umbrellux DAO, HistDAO (Xymogen) and Histamine Block (Seeking Health).  Other products that claim to contain DAO enzyme are misleading.

DAOsin is available in Europe.

Financial Disclosure: I have developed education programs with funding from Umbrellux in the past.

Trying the Supplement

DAO enzyme breaks histamine down immediately so you will know quickly if this supplement will improve your symptoms. Umbrellux offers a sample kit with ten tablets for ten dollars, plus shipping. 

Readers often want to know how they should trial the supplement. There is no “right way.” 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.


If you would like to leave a comment, there is a box at the bottom of this page.

41 Responses

  1. For a vegan option, you can buy Naturedao from Amazon.co.uk (UK) . I just ordered 3 (the maximum allowed to ship to Canada.) It cost me $50/ 60 caps box) – $154 Canadian dollars, with the current exchange, for 3 boxes of 60 capsules, including shipping. This seems about the price of the pork-based DAO from the USA.

    I am not vegetarian. (All I can eat seems to be meat. Most vegetables, which I love, make me terribly ill…) But as I have never felt any relief from Daosin, I am eager to try Naturedao. Comments on Amazon.co.uk mention it helped some people more than Daosin ever did…

    Amazon.co.uk uses the same info as Amazon.ca accounts (I.D., password, payment.)

    And, just putting Naturedao in my cart got me a free 1 month trial of Prime.

    I knew I could get a free 1 month trial both from Amazon.com (USA) and Amazon.ca (Canada.) But I had no idea I could get a third month free every year to watch Prime videos (I love The Grand Tour!) They actually activated my free trial BEFORE I made the purchase from the checkout… During this pandemic, it is nice to have another entertainment resource besides Netflix, and even nicer to get it for free. I bing watch, then cancel before the month is over. I have done this for a few years, so it works! I just need to schedule an alarm to remember to cancel the subscription in time.

    I hope Naturedao will help. If not, I will get some (free) laughs from Amazon… Good luck to us all!

  2. I got dizzy after taking histDAO. Not sure if I should try another brand or what. I am able to eat pork sausages do not sure if I am reacting to the pork itself. What are alternative Dao supplements?

    1. Hi Lisa – all the brands will have the same active ingredients, but the expedients may be different. Naturdao® is a different form of DAO (vegetable-based), but it is not currently available in Canada/US.

    1. I have left messages with a few different companies to see if the Amy Myers Histazyme contains “true” DAO, but I have not had a reply.

      The last time I researched this topic (about 1.5 years ago), DAO was only available in a few products. However, that may have changed. From the Amy Myers supplement advertisement, it looks like it is a reputable product.

  3. HELLO! DO you have t take Dao every day? Is there a need to build it up, or is it immediate, in terms of relief? Confused as to dosing. THANK YOU! CAROLE FIELD

    1. Unfortunately, I don’t think there are any products for sale directly in Canada. You need to order from the US, which is difficult at this time.

  4. Hi Wendy, what’s your opinion on Naturdao (from Spain). It claims to pack 1,000,000 HDU per pill. It’s derived from legumes (sprouts?). I just began taking HistDao (I live in Canada), however I’d rather take something more natural (but just as strong). Thoughts?

    1. Hi Dalton- I have only seen a few studies regarding stability but have not seen any clinical trials. However, even if there was research, there seems to be a lot of individual variation with DAO supplements – so the best bet is to try the product and see if you notice any benefit. Unfortunately, NaturDAO is not available in Canada at this time. If anybody else knows when it will be available outside of Europe, please post.

  5. Hello, so pleased to have found your website and infos. A blood test recently showed very low levels of DAO, however, I have no symptoms EXCEPT very painful periods & migraines before my period. According to my naturopath, high histamine levels during menstruation release prostaglandins and that is what causes the pain & migraines. I was wondering: would taking a DAO supplement during the days of my period lower the histamine ‘response’?

    1. Hi Lucie- almost everything regarding histamine intolerance is speculation and theory. Health care professionals often talk about the theories as if they are fact, but this is not the case.
      The DAO supplement breaks down histamine in food. It is not absorbed into the blood, so it probably would not improve your menstruation related symptoms.
      I hope that helps, Wendy

  6. I want to know whether taking umbrellox DAO everyday, even with meals with low histamine, can increase my body’s own DAO level.

    1. Hi Maritza – Unfortunately, a DAO tablet won’t increase your blood levels of DAO. It is not absorbed into the body.

  7. 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,

    1. 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.

  8. 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

    1. 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.

  9. 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

    1. 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.

  10. 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.

    1. 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:

  11. 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,

    1. Hi RG – HistDAO is made by Xymogen. It is the same thing as the other DAO supplements from Sciotec, such as DAOsin.

    1. 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/

          1. You can buy Naturedao from Amazon.co.uk (UK) . I just ordered 3 (the maximum allowed to ship to Canada.) It cost me $50/ 60 caps box) – $154 Canadian dollars, with the current exchange, for 3 boxes of 60 capsules, including shipping.

            It uses the same id, password, and payment from my Amazon.ca account.

            And I got a free 1 month trial of Prime. I knew I could get a free 1 month trial both from Amazon.com (USA) and Amazon.ca (Canada.) But I had no idea I could get a third month free every year to watch Prime videos (I love The Grand Tour!) They actually activated my free trial BEFORE I placed the purchase from the checkout… During the pandemic, it is nice to have another entertainment resource besides Netflix, and even nicer to get it for free. I bing watch, then cancel before the month is over. Yeah! I have done this for a few years, so it works! I just need to schedule an alarm to remember to cancel the subscription in time.

  12. 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.

    1. 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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