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Diamine Oxidase (DAO) Enzyme: What is HDU?

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The Role of DAO in Histamine Intolerance and the Significance of HDU

The enzyme Diamine Oxidase (DAO) is an enzyme with a pivotal role in our digestive processes. Its presence in our bodies, specifically the digestive system, enables the breakdown and neutralization of a bioactive compound known as histamine. The enzymatic activity of DAO and its function in managing inflammation and allergies is crucial to our overall well-being.

DAO, at its core, is an enzyme responsible for the metabolic breakdown of histamine. Our bodies produce DAO naturally, and certain foods are rich sources of this enzyme. Enhanced DAO levels potentially contribute to the effective management of histamine levels in the body, thereby impacting our overall health.

Histamine: Understanding Its Role and Effects

Histamine is a compound that plays a key role in local immune responses. It contributes to the dilation of blood vessels, thereby facilitating the flow of blood to areas of injury or infection. Additionally, histamine is responsible for gastric acid secretion, a process vital to digestion.

However, an imbalance of histamine levels can lead to histamine intolerance. This condition manifests when the body is unable to break down histamine efficiently, typically due to a deficit in the diamine oxidase enzyme. Consequently, the body’s histamine load escalates, leading to symptoms of histamine intolerance.

Factors that Affect Histamine Levels

The body’s histamine levels are influenced by a diverse array of factors ranging from genetics to lifestyle choices. Understanding these factors can help in comprehending the complex interplay between the DAO enzyme and histamine.

  1. Genetics: Our genetic blueprint plays a significant role in histamine regulation. Variations or mutations in the gene responsible for producing the DAO enzyme can affect its production and subsequently, the amounts of histamine levels, leading to an imbalance.
  2. Medications: Certain medications, including acetylcysteine, a phlegm reducer, and both over-the-counter and prescription nonsteroidal anti-inflammatory drugs (NSAIDs), can interfere with DAO functions or inhibit its production, impacting the body’s ability to manage histamine levels effectively.
  3. Foods: Diet significantly influences histamine levels. Foods high in histamine, such as alcohol, aged cheeses, fermented products, packaged meats, legumes, and citrus fruits, can potentially increase the body’s histamine levels.
  4. Health Conditions: Certain health conditions, especially those that damage the lining of the gut, can lead to histamine intolerance, a condition characterized by the body’s inability to degrade histamine efficiently.
  5. Environmental Factors: Excessive heat exposure can trigger histamine intolerance in some individuals, thereby affecting histamine levels.
  6. Physical Activity: Strenuous exercise, while beneficial for overall health, can transiently increase histamine levels in the body.
  7. Biogenic Amines: Certain biogenic amines can enhance the sensitivity of individuals to histamine ingestion, thereby influencing the body’s response to histamine levels.

Recognizing Histamine Intolerance and Its Symptoms

Histamine intolerance symptoms can include headaches, skin rashes, nasal congestion, and abdominal pain. These symptoms often resemble those of common allergies, complicating the diagnostic process. However, blood tests, dietary lists, and understanding a patient’s history can aid in diagnosing histamine intolerance accurately.

For people with histamine intolerance, an excess of histamine can trigger uncomfortable symptoms, which can range from mild to severe. In some cases, this may occur due to a genetic mutation affecting the diamine oxidase gene, leading to reduced DAO serum activities and an inability to adequately degrade histamine.

Histamine Degradation Unit (HDU): A Measure of DAO Activity

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In the context of histamine and DAO, HDU or Histamine Degradation Unit is a critical measurement. It offers a quantifiable indication of how effective the diamine oxidase enzyme is at metabolizing histamine. One HDU is defined as the amount of DAO that degrades 1 pmol (0.11 ng) of histamine per minute. High HDU values signify effective histamine breakdown, while low values might indicate the presence of histamine intolerance.

DAO, histamine, and HDU are interconnected in ways that significantly impact our health. When HDU values dip, the DAO-Histamine reaction is affected, leading to an accumulation of histamine. Persistent histamine excess can result in chronic inflammation, allergic reactions, and other adverse health effects.

Methods to Measure Histamine Degradation

Several methods have been developed to measure the rate of histamine degradation in the body. These methods provide essential information about histamine and DAO activity, contributing to our understanding of conditions such as histamine intolerance.

1. Enzymatic AssaysMeasures the rate of degradation of amino substrates during the oxidative deamination reaction catalyzed by DAO. The results are given in HDU/mL.
2. Skin Prick TestingA diagnostic tool for type-I allergies. When used for measuring histamine degradation, N-methyl-transferase, not DAO, is identified as the primary enzyme for histamine degradation.
3. Histamine Enzyme Immunoassay KitA kit designed to measure histamine levels in plasma samples, providing a quantitative determination of histamine degradation by DAO. Results are given as HDU/mL.
4. Liquid Chromatography Coupled to Mass SpectrometryAn advanced technique used to quantify histamine levels in tissue samples. It involves separating components in the sample and subsequently identifying and quantifying these components.

Importance of a Balanced Histamine Diet

For patients with histamine intolerance, an integral part of management involves paying attention to your diet. A diet with an excessive histamine content can exacerbate symptoms. High-histamine foods such as fermented cheeses, wines, and certain types of fish may increase the body’s histamine level, worsening symptoms in those with histamine intolerance.

A low-histamine diet, on the other hand, can offer relief. This involves the consumption of foods low in histamine and avoiding histamine liberators—foods that trigger the release of histamine. A clear, well-organized food list that highlights low and high-histamine foods can be instrumental in managing this condition.

Low-histamine Alternatives

Navigating dietary choices can be challenging for individuals dealing with histamine intolerance. The following table provides a helpful comparison between high-histamine foods and their low-histamine alternatives, enabling you to make informed decisions that can assist in managing this condition.

Foods High in HistamineLow-Histamine Alternatives
Fermented foods (e.g. sauerkraut, kimchi, yogurt)Fresh, unprocessed produce
Aged cheesesDairy substitutes (e.g. almond- and coconut-based products)
Processed meats (e.g. salami, ham, sausages)Fresh meat and fish (not aged or ground)
ShellfishFresh fish (not aged or ground)
SpinachMost fresh herbs (e.g. basil, cilantro, parsley)
TomatoesCertain vegetables (e.g. squash, sweetcorn, watercress)
Citrus fruitsCertain fruits (e.g. apple, apricot, cantaloupe, cherries, grapes, kiwi, nectarine, passion fruit, peach, pear)
ChocolateSweeteners (e.g. stevia, monk fruit, inulin)
AlcoholHerbal teas (e.g. chamomile, peppermint)
Wheat germGluten-free grains (e.g. quinoa)

DAO Supplements and Histamine Blockers

Apart from dietary adjustments, dietary and food supplements can be beneficial for managing histamine intolerance. DAO supplements, derived from a vegetable source, are a common natural method to augment the body’s DAO levels. They boost the enzymatic activity of DAO, thereby aiding in the efficient breakdown of excess histamine.

Histamine blockers are another potential recourse. These medications obstruct histamine receptors, thereby inhibiting the adverse reactions triggered by an excessive release of histamine. The use of these blockers should, however, be done under medical advice to prevent any potential adverse effects.


In the vast web of our bodily functions, understanding the diamine oxidase enzyme’s role, the balance between histamine and DAO, and the concept of HDU is crucial. A holistic approach that involves dietary adjustments, the use of nutritional supplements, and medical advice can help manage histamine intolerance effectively. The journey toward managing histamine intolerance is a continuous one, but with the right knowledge and guidance, it is entirely manageable.

Embrace a Healthy Balance with SeeBeyond Shop’s DAO-HIST Supplements

SeeBeyond Shop is your partner in navigating the complex interplay of histamine, DAO, and HDU. We harness the power of nutritional science to formulate our DAO-HIST supplement, designed to boost DAO levels and promote efficient histamine breakdown. By understanding your body’s HDU values, you can take control of your health journey more effectively.

Don’t let histamine imbalance hold you back. Contact our team of professionals at SeeBeyond Shop today, and let us guide you toward the vibrant health you deserve. It’s time to see beyond histamine intolerance and towards a future of well-being.

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