05/12/2026
Diamine oxidase, or DAO, is an enzyme produced primarily in the gut to break down histamine from food or the gut microbiome. The small amounts of histamine obtained from foods or from the gut microbiome are usually broken down in the intestines by diamine oxidase (DAO).
However, when there is damage in the intestines or genetic impairment of DAO, the histamine from foods can be enough to trigger systemic reactions. The DAO enzyme is encoded by the AOC1 gene. Genetic variants in AOC1 can decrease the production of the DAO enzyme.
DAO is readily available as a supplement, and a number of studies and clinical trials have investigated whether it is helpful for a variety of histamine symptoms.
Gastrointestinal and respiratory symptoms:
A small clinical trial examined the effect of DAO supplements in people with low serum DAO and nonspecific, recurrent gastrointestinal problems while on a low histamine diet. The study participants took 4.2 mg of extracted porcine kidney protein containing 0.3 mg of DAO before meals for one month. Results showed a significant reduction in gastrointestinal symptoms such as reduced bloating, diarrhea, constipation, nausea, abdominal pain and bloating. There was also a reduction in heart palpitations, headaches, nasal congestion, sinus drainage, and asthma symptoms. After stopping the DAO supplements for four weeks, the respiratory and gastrointestinal symptoms returned to some extent.
Migraines: A placebo-controlled, double-blind study of DAO supplements for migraine found that there was a significant reduction in hours of pain. In the study, DAO enzyme supplements were taken with meals for one month.
Hives (urticaria): In people with chronic urticaria, DAO supplementation reduced hives, but only in a subset of participants who had low serum DAO levels at baseline.
Histamine intolerance: A pilot study using DAO capsules before meals showed that all histamine intolerance symptoms were significantly reduced after four weeks.
Gut motility: In a mouse model of irritable bowel syndrome (IBS), DAO supplements derived from pea shoots were shown to reduce the overactive intestinal motility associated with high histamine levels. The study also showed that rectally administered DAO was effective.
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This is just a short excerpt from my in-depth article on DAO. Here is the link to my full article: www.geneticlifehacks.com/dao-enzyme-supplements-research-studies-and-genetic-connections/
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DAO enzyme supplements work by providing the enzyme needed to break down histamine in food and from the gut microbiome.