Are you curious about histamine intolerance and noticed the term diamine oxidase deficiency?
Wondering what it really means?
Diamine oxidase [DAO} deficiency is often pinpointed as a key contributor to histamine intolerance, yet clear, actionable information can be hard to find.
In this blog, we break down what you need to know about diamine oxidase deficiency, along with practical tips for identifying and managing the condition.
Understanding diamine oxidase
Enzymes: Small Proteins, Big Roles
Our bodies rely on thousands of enzymes—tiny but powerful proteins that accelerate essential chemical reactions in digestion, metabolism, and more. Without enzymes, these reactions would crawl along too slowly, preventing our bodies from functioning optimally.
Diamine Oxidase: What’s Its Job?
Diamine oxidase (DAO) is a critical enzyme for breaking down histamine, mainly found in the intestines, kidneys, and placenta. In the intestines, DAO actively breaks down dietary histamine, helping prevent it from entering the bloodstream. (1)
DAO Deficiency: What’s Happening?
If you’re low on DAO, excess histamine can seep into the bloodstream, impacting other body systems. DAO deficiency is linked to histamine intolerance, where histamine builds up and triggers various symptoms. (1)
Causes of DAO Deficiency
Genetics
Genetics Your DNA can influence enzyme function, including DAO. Genetic variations (polymorphisms) can reduce DAO efficiency, leading to deficiency. (2)
A few of these polymorphisms are shown in the diagram below.
Existing health conditions
Existing Health Conditions DAO is found in intestinal epithelial cells, so conditions like Crohn’s disease or Coeliac disease that harm these cells can impact DAO availability.(3)
Medications
Medications Certain medications unintentionally impact DAO activity, leading to deficiency. Examples include verapamil (blood pressure medication), clavulanic acid (antibiotic), and amitriptyline (antidepressant).(4)
Note: Please consult your doctor before making any changes to your medications.
Alcohol
Alcohol Alcohol is a well-known DAO inhibitor, but its effects are temporary—DAO activity will resume after alcohol exits the system.(3)
Recognising the signs of DAO deficiency
When you are deficient in DAO, your body struggles to break down histamine, which then builds up in your blood and can cause histamine intolerance. Therefore, the symptoms of DAO deficiency match those of histamine intolerance.
The body systems that are affected and the subsequent symptoms that develop are detailed in the diagram below.(5)
The most common symptom of histamine intolerance, and therefore of DAO deficiency, is bloating, followed by postprandial fullness, which is a prolonged feeling of fullness after a meal. Other gastrointestinal symptoms including diarrhoea and abdominal pain rank highly in frequency, alongside other symptoms such as dizziness, headache and itchy skin.(6)
Diagnosing DAO deficiency
Though there’s no gold-standard test for DAO deficiency, several options may help:
Serum DAO levels
Low blood DAO levels suggest deficiency, though this measurement may not fully reflect intestinal DAO activity. (7, 8)
Colon Biopsy
During an endoscopy, tissue samples from the colon can be examined for DAO levels, potentially providing a more accurate assessment.(9)
Genetic Testing
Testing DNA can reveal genetic mutations associated with low DAO function. This approach is effective if genetics are the root cause, but won’t capture other contributing factors. (8)
Histamine free diet
For a more accurate assessment, try a histamine-free diet for 4-8 weeks. If symptoms improve, gradually reintroducing histamine-rich foods can help gauge tolerance levels.(9)
Other Conditions to Rule Out
Before diagnosing DAO deficiency, it’s crucial to rule out other conditions with similar symptoms, like:
These tests include:
- Food allergies (via skin prick test)
- Mastocytosis (using serum tryptase tests)
- Chronic gastrointestinal conditions (e.g., Crohn’s, coeliac disease)
- Effects of current medications (9)
Managing DAO Deficiency Through Diet
The most effective approach to manage DAO deficiency is a low-histamine diet. Although completely avoiding histamine is challenging, reducing certain foods can alleviate symptoms
Foods to avoid:
There can be a lot of variation between different sources on which foods to avoid. The ones below are the most commonly agreed upon:
- Canned or fermented fish products e.g. canned tuna, sardines and mackerel, fish sauce
- Certain types of fish e.g. tuna, salmon, mackerel, sardines, anchovy, herring, swordfish
- Matured or ripened cheese e.g. parmesan. Grana Padano, gouda, cheddar, feta, camembert
- Cured meat e.g. sausages, bacon, salami, pancetta
- Certain vegetables e.g. tomato, spinach, sauerkraut, aubergine and avocado
- Certain fruits e.g. citrus fruits, strawberries, bananas, plums, kiwi, pineapple, pears
- Fermented alcohols e.g. beer, wine
- Other fermented products e.g. soy sauce, miso, tempeh
- Nuts and chocolate (8, 10)
Keeping a balanced diet
You can still enjoy a balanced, healthy diet even while reducing histamine intake. Here’s how:
- Eat Fresh: Histamine levels increase as food ages, so aim to eat foods shortly after purchasing.(11)
- Get Your Five-a-Day: Many fruits and vegetables are still on the menu.
- Choose Omega-3 Sources Carefully: While oily fish is usually high in histamine, you can get omega-3s from fresh white fish (like sea bass) or plant-based sources.(12)
- Limit Alcohol: Besides being a DAO inhibitor, fermented drinks like beer and wine contain high histamine levels.
DAO Supplements: What Does the Research Say?
In addition to dietary changes, DAO supplements derived from porcine (pig) kidneys are available, mimicking human DAO activity.
Research Insights
Studies show promising symptom relief with DAO supplements, although more research on long-term effects is needed. These studies have generally been small and short-term, so further investigation is essential. (9)
Thinking About Trying a DAO Supplement?
If you’re curious about trying a DAO supplement, it can be a helpful tool for managing histamine intolerance symptoms. DAO works by supporting your body’s natural ability to break down dietary histamine, which may provide relief for some individuals.
I personally use and recommend the porcine DAO enzyme from Tolerance. I’m happy to share an exclusive 10% discount with the code TDE-10. If you’d like to try it, simply apply the code at checkout.
While it’s not a cure, it can be a game-changer for managing histamine-related symptoms when used as part of a broader approach. As always, consult with a healthcare professional before introducing any new supplement to ensure it’s the right fit for your needs.
Remember, it’s important to consult with a healthcare professional before starting any new supplement.
Takeaway points
- DAO is essential for breaking down histamine, and deficiency can lead to histamine intolerance.
- Causes of deficiency range from genetic and health conditions to medications and lifestyle factors.
- Symptoms can be present over several different body systems.
- Symptoms vary across body systems but are often digestive or systemic (like skin issues and headaches).
- The most reliable way to manage DAO deficiency is a low-histamine diet, though DAO supplements may help for some people.
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Health Disclaimer: The information provided on this website is for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your medical team or other qualified health provider with any questions you may have regarding a medical condition or dietary changes. The views expressed on this site are based on the best knowledge of the dietitian. Readers are advised to consider their personal health needs before implementing any nutrition strategy.
Nichola Williams, MNutr, RD
Nichola specialises in histamine intolerance and personally manages the condition, bringing both clinical and lived experience to everything she writes.
Lily Sconce
Lily is a third-year student dietitian, with an interest in physiology and gastrointestinal conditions. She brings an enthusiasm to learn new things and to better understand the role that food has in maintaining good health. Outside of studying, Lily enjoys hiking in various locations across the country and trying out new recipes at home. She looks forward to putting her training to use in a clinical setting once she graduates.