Dr Janice Joneja, a world expert on histamine intolerance, has published two books on histamine intolerance:

A Beginner's Guide to Histamine Intolerance – read more about it here.

Buy the paperback from Amazon here; buy the e-book from Amazon here.

Histamine Intolerance: The Comprehensive Guide for Healthcare Professionals – read more about it here.

Buy the ebook from Amazon here.

You can buy all of Dr Joneja's books here in the UK or here in the US.

We receive many enquiries about diamine oxidase (DAO) about which there is a great deal of misunderstanding. The questions asked are usually some version of the following:

1.  How can I increase my own DAO levels?
2. Will taking DAO supplements regularly increase my DAO?
3. Will DAO supplements cure me of histamine intolerance?
4. Which DAO supplements are safe for me?
5. What side-effects can I expect from DAO supplements?

For those readers new to the field, a few words about diamine oxidase (DAO) is in order. 

Histamine intolerance or sensitivity is caused by a build-up of histamine in the body to a level that exceeds the amount required for normal functioning.  The excess histamine results in symptoms that resemble allergy.  Under normal conditions, excess histamine is broken down by specific enzymes, especially diamine oxidase (DAO).   The products of histamine breakdown are then excreted via the kidneys in urine.  Usually this will ensure that histamine levels do not exceed a person’s “limit of tolerance” (the level above which symptoms develop).  However, when the amount of DAO is insufficient to deal with the excess, histamine levels rise and typical histamine sensitivity symptoms develop. Please see this article.  

DAO acts on histamine both inside and outside the body. Within the body, DAO is found principally in the kidneys, thymus, and the placenta in pregnant women. When histamine levels inside the body become excessive, DAO, and another enzyme called histamine N-methyl transferase (HNMT) break down the excess.  Excess histamine can rise inside the body (called endogenous histamine) as it is released from mast cells in a number of conditions including allergy, mast cell activation disorders, chronic inflammation, infection, and trauma, among others.

The digestive canal is essentially an area outside the body as materials enter at one end and exit at the other.  Only the digested products enter the body through the epithelium and pass into circulation. DAO is found in the ileum and jejunum of the small intestine.  It mixes with food, beverages and other ingested materials as they pass through the digestive tract.  As the DAO encounters histamine in these substances, it breaks it down, thus preventing this external source of histamine (called exogenous histamine) from entering the body.  When DAO is adequate and functioning efficiently, almost 99% of exogenous histamine is broken down within the digestive tract lumen and removed before it can enter the body.  It is estimated that only about 1% of histamine from this source actually enters circulation.  When DAO is deficient, far more histamine enters and builds up within the body.

DAO supplements are designed to increase the DAO in the digestive tract and enhance breakdown of histamine within the contents of the digestive canal.  Unlike supplements of vitamins, minerals and other nutrients, DAO does not enter into circulation and therefore will not increase the amount of DAO inside the body.  DAO must be taken very shortly before meals as it has a short “half-life” - the time it takes for the enzyme to become inactive.  Its effect is limited to the degree of breakdown of histamine in the dietary components with which it is mixed for a fairly short as the food passes through the digestive canal. 

Obviously, the amount of histamine entering the body from dietary sources can be significantly reduced by following a histamine-restricted diet. (See the second half of this article.) A low-histamine diet, plus supplemental DAO should reduce the amount of exogenous histamine entering the body to almost nil.  It is very important to understand that supplemental DAO and a histamine-restricted diet will not reduce the amount of histamine produced within the body.  The effects of this histamine must be addressed by other methods of control such as antihistamines, allergy management programs, mast cells stabilizers and other appropriate therapies depending on the source of the endogenous histamine.

Now to address the specific questions listed above:

1. Your diamine oxidase (DAO) production is an individual characteristic.  The amount produced in each of the organs in your body is determined by your inherited genetics.  As with most enzymes in your body, there is no way that you can increase the amount your body manufactures. The major organs that produce DAO include the jejunum and Ileum in the small intestine, the kidneys, the thymus, and the placenta in pregnant women.
   
   
2. There are a number of supplements now available over-the- counter, without a prescription, that contain varying levels of diamine oxidase.  As few brands include DAOSin (Sciotec), DAO Histaminase (AllergyResearchGroup), Histame (Seeking Health), HistamAid88 (Swanson), and Dao Histamine Digester Supplement (Nutricology), among others. Some of these have additional ingredients such as quercetin, rutin, vitamins (mainly vitamin C), and minerals such as calcium, as well as the emulsifiers, stabilizers, and preservatives as needed in most similar manufactured products to ensure safety and increased “shelf life”.  The number of manufacturers producing the supplements has increased amazingly since histamine intolerance has become more widely known in the past two or three years. 
   
   As you will understand from my introductory explanation, DAO from supplements does not enter the body; it will not increase you internal DAO, so taking the supplement regularly will only affect the amount of histamine in the food and beverages you consume after taking it. The DAO in supplements is not a medication – it is a supplement comparable to lactase (the enzyme that breaks down lactose in milk) in supplements such as Lactaid and Lacteez which, taken together with milk, break down lactose and prevent the adverse effects of excess lactose in the bowel. Lactase, like DAO, acts on the food in the digestive canal; it does not enter the body itself.
   
   
3. Taking DAO supplements will not cure histamine intolerance: the supplement will reduce the amount of histamine entering the body and thus decrease the total level of histamine within the body (endogenous plus exogenous histamine) by removing the exogenous source.  This may be sufficient to reduce the total to below the person’s limit of tolerance, and therefore provide symptomatic relief.  Whenever the same person’s total level of histamine from both internal and external sources exceeds their limit of tolerance in the future, symptoms will develop.  The only way to effect a cure for histamine intolerance is to find the cause of the excess histamine and treat that.  If the underlying cause is found to be a DAO deficiency, a histamine-restricted diet, plus supplemental DAO should enable the sufferer to remain relatively symptom-free.  However, it is important to understand that there are many different reasons for a person to have an excess of histamine in their body and all these should be investigated before reaching the conclusion that DAO deficiency is the cause.
   
   
4. Because DAO is not absorbed into the body, the DAO enzyme itself will not produce any harmful effects.  Any adverse reactions to the supplement will be due to the additional ingredients in the supplement that have been absorbed into the body.  If you have concerns about these additives, be careful to read the list of ingredients on the product label, or apply to the manufacturer for such information.  Manufacturers change the formulations of their products frequently in response to consumers’ concerns so be diligent in obtaining up-to-date lists of ingredients in any supplement you purchase.  I would recommend that to be as safe as possible, you should purchase the supplement with the fewest additional ingredients, and obviously avoid those that contain anything to which you know you are intolerant or allergic.
   
   
5. The adverse effects that you might expect from the supplement will be due to your response to the additional ingredients in the product.  As I have repeatedly emphasised, because DAO is not absorbed, you will not experience any adverse effects from the enzyme itself.

August 2016

You can buy DAO supplements here in the UK or here in the US.
You can buy all of Dr Joneja's books here in the UK or here in the US.

If you found this article interesting you can find a number of other articles on histamine intolerance both by Dr Joneja and others here, reports on histamine research here and a Q & A section on histamine with Dr Joneja here.

For many, many other articles on every type of food allergy and intolerance click here; for coeliac disease and other food related conditions, go here.

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Dr Janice Joneja, Ph.D., RDDr. Janice Joneja is a researcher, educator, author, and clinical counsellor with over thirty years of experience in the area of biochemical and immunological reactions involved in food allergy and intolerances. Dr. Joneja holds a Ph.D. in medical microbiology and immunology and is a registered dietitian (RD). 

She has been a member of the faculty at several Canadian universities, starting her career as an Assistant Professor in the Department of Microbiology, Faculty of Science, and in the Faculty of Dentistry, at the University of British Columbia, Vancouver. Since 2001 Dr. Joneja has been a faculty member in the School of Biomedical and Molecular Sciences, at the University of Surrey, in England, teaching in the M.Sc. course in Nutritional Medicine.  For 12 years she was head of the Allergy Nutrition Program at the Vancouver Hospital and Health Sciences Centre.

Dr. Joneja is the author of six books and a dietetic practice manual on food allergy, a textbook on Irritable Bowel Syndrome, and several distance education courses. Her most recent books include “The Health Professional’s Guide to Food Allergies and Intolerances”, “Dealing with Food Allergies”, and “Dealing with Food Allergies in Babies and Children”.  Dr. Joneja’s work has been published in peer-reviewed scientific and medical journals, as well as in popular magazines.  She is a respected lecturer at universities, colleges and hospitals internationally, and regularly appears on television and radio call-in shows as an expert in her field.

Dr. Joneja is President of Vickerstaff Health Services, Inc., a practice that provides counselling for people suffering from all aspects of adverse reactions to food, and resources for the professionals and care-givers who support them.

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