What is DAO Deficiency? A Quick Refresher
If you experience uncomfortable symptoms after eating certain foods, you may have come across the term ‘histamine intolerance’. One of the most common reasons people experience this sensitivity is a reduced ability to break down histamine found in food. This job belongs to an important enzyme in your gut called diamine oxidase, or DAO.
When your DAO enzyme levels are low, or the enzyme isn’t working as well as it should, histamine from your diet may not be broken down efficiently. It can then build up in your system and contribute to a wide range of symptoms. This state is known as DAO deficiency. But what causes it? The answer generally falls into one of two categories: the blueprint you were born with, or factors you have encountered throughout your life.
Genetic DAO Deficiency
Your DNA contains genes, which are the instructions for building everything in your body, including enzymes. The instructions for making the DAO enzyme are found in a gene called AOC1, which is one of the two primary genes that influence histamine regulation within your body.
Sometimes, there are small, common variations in the genetic code. These are known as Single Nucleotide Polymorphisms, or SNPs (pronounced ‘snips’). You can think of a SNP as a tiny spelling variation in a word. Most of the time, these variations have no effect. However, some SNPs in the AOC1 gene are associated with the production of a less effective DAO enzyme, or lower levels of it altogether.
If you inherit these particular SNPs from your parents, you may have a genetic predisposition to lower DAO activity. This doesn't mean you will definitely experience symptoms of histamine intolerance, but it might mean your baseline capacity for breaking down dietary histamine is naturally lower than someone without these genetic variants. It's an indicator, not a diagnosis. A genetic test is the only way to identify these specific SNPs in your AOC1 gene.
Acquired DAO Deficiency
It is also possible to develop DAO deficiency during your lifetime, regardless of your genetic makeup. This is known as ‘acquired’ DAO deficiency, because it is caused by external factors that reduce your DAO levels or interfere with the enzyme’s ability to function. Unlike a genetic predisposition, acquired DAO deficiency can sometimes be temporary, especially if the underlying cause is identified and addressed.
Gut Health is Key
The vast majority of your DAO enzyme is produced and stored in the lining of your small intestine. Therefore, anything that damages this delicate lining can reduce your ability to produce enough DAO. Health conditions that affect the gut, such as inflammatory bowel disease (IBD), coeliac disease, and Small Intestinal Bacterial Overgrowth (SIBO), are often linked with lower DAO levels for this reason.
The Role of Medications
Research suggests that a number of common medications can interfere with the DAO enzyme. Some appear to block the enzyme’s activity directly, while others may reduce its production. If you are concerned about your medication, it is essential to speak with your doctor or pharmacist; never stop taking prescribed medication without professional medical advice.
Nutrients and Diet
Like many processes in the body, the DAO enzyme needs specific vitamins and minerals to work properly. These are often called ‘cofactors’. Key cofactors for DAO include vitamin C, vitamin B6, copper, and zinc. A diet lacking in these nutrients could potentially impair DAO function. Furthermore, alcohol is recognised as a potent inhibitor of the DAO enzyme, which helps to explain why wine and beer can be significant triggers for some people.
We explore each of these reasons in more detail in our article dedicated to looking at non-genetic causes of DAO deficiency.
Can You Have Both?
Yes, and it is often quite common. A person can have both a genetic predisposition to lower DAO activity, and one or more acquired factors on top that push them over the edge. For instance, someone with relevant AOC1 gene SNPs might have managed perfectly well for years. Then, a period of high stress, a gut infection, or a new medication could become the ‘tipping point’ that causes their DAO levels to fall low enough for symptoms to appear.
This combination helps to explain why histamine intolerance can seem to appear suddenly in adulthood. The underlying genetic tendency may have always been there, but it took an acquired factor to reveal it.
How to Investigate the Cause
Understanding whether your DAO deficiency has genetic or acquired roots (or both) can help you and your healthcare provider create a more effective management plan.
- Working with a professional: A registered dietitian or qualified healthcare practitioner can conduct a thorough review of your health history, diet, lifestyle, and medications to identify potential acquired causes. They can help you explore gut health, nutrient status, and other contributing factors. We have a list if trusted professionals on our About page that you can reach out to if you need to speak to someone
- The role of genetic testing: A simple cheek-swab genetic test can reveal if you carry SNPs in the AOC1 gene associated with a predisposition to reduced DAO activity. This information provides a foundational piece of your personal health puzzle
These two approaches are complementary. If a genetic test shows no variants linked to low DAO, it may encourage a deeper investigation into acquired causes. If the test does show a predisposition, it can validate your experiences and highlight the importance of proactively supporting your gut health and managing other triggers.
Empowering Your Health
Whether your DAO deficiency is primarily genetic or acquired, the goal is the same: to support your body’s ability to process histamine. If acquired factors are at play, working with a professional to address the root cause is the primary focus.
If a genetic predisposition is involved, the strategy is often about long-term support. This can include being mindful of your total histamine load from food, ensuring your diet is rich in the nutrient cofactors DAO needs, and protecting your gut health. For some people with recognised DAO deficiency, supplementing with a diamine oxidase enzyme before a high-histamine meal may help with the digestion of histamine from food.
Understanding the 'why' behind your symptoms is a powerful first step. It shifts your focus from wondering what is wrong, to wondering how you can move forward, and make informed decisions about your health and wellbeing.
This article is for informational purposes only and is not intended as medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare professional or registered dietitian with any questions you may have regarding a medical condition or dietary changes.