monoamine oxidase (MAO)
An enzyme that breaks down biogenic amines, such as tyramine or serotonin. It also completes the degradation of histamine after it has been processed by HNMT.
Monoamine oxidase comes in two forms, MAO-A and MAO-B. Both are responsible for breaking down substances such as tyramine, serotonin, dopamine, or adrenaline. MAO's connection to histamine is indirect, yet important. Once HNMT processes histamine into N-methylhistamine, MAO-B takes care of the next step. If this process stalls, intermediate metabolites accumulate in the body.
In practice, MAO is particularly interesting because of tyramine. There is a group of medications that block MAO. These include certain antidepressants, as well as the antibiotic linezolid and medications for Parkinson's disease. Those taking them cannot break down tyramine from food. Eating aged cheese, cured meats, or drinking red wine can then cause a sharp spike in blood pressure. This reaction is known as the "cheese effect" and manifests as a severe headache, heart palpitations, and sweating.
However, the risk is evaluated more mildly today than in the past. Modern production methods and hygiene standards have lowered tyramine levels in many cheeses and beverages, so the strictness of the diet depends on the specific medication and its dosage.
For people with suspected histamine intolerance, MAO has another significance. Tyramine-rich foods largely overlap with those high in histamine. Therefore, for some individuals, tyramine—rather than histamine—may actually be the culprit behind their symptoms. It pays to track which specific foods trigger these issues.
Related terms
The main enzyme responsible for breaking down histamine in the body. Its deficiency is related to HIT.
The second major enzyme responsible for breaking down histamine. Unlike DAO, it works inside cells within the brain, lungs, skin, and liver. It cannot be supplemented in capsule form.
DAO enzyme supplementation for better breakdown of dietary histamine in people with HIT.
Substances that reduce the activity of the DAO enzyme, which worsens the breakdown of histamine.
Substances that the DAO enzyme needs to do its job, mainly copper and vitamin B6. Without them, the enzyme cannot work at full capacity, even if there is enough of it in the body.