Histamine

Histamine is a biogenic amine with many functions: immune response, stomach acid production, neurotransmitter. With histamine intolerance, the activity of the breakdown enzyme DAO (diamine oxidase) is often reduced – histamine from food is then broken down more slowly. Complaints typically occur shortly after eating. Studies have observed a link with a more permeable gut barrier and altered gut flora.

The value is measured in stool. There, histamine is formed by gut bacteria; raised values are found with dysbiosis and with DAO deficiency. Together with the DAO enzyme it shows whether the formation or the breakdown of histamine is more likely to be altered.

What histamine does in the body

Histamine is made from the amino acid histidine; the enzyme histidine decarboxylase needs vitamin B6 for this. The body stores it mainly in mast cells and white blood cells, in certain cells of the stomach lining and in nerve cells. It acts via four receptor types: H1 widens blood vessels, makes them more permeable, triggers itching and constricts the bronchi; H2 stimulates stomach acid and speeds up the heartbeat; H3 controls wakefulness in the brain and the release of other messengers; H4 directs immune cells. In the gut, histamine also comes from food – especially aged and fermented foods – and from gut bacteria that convert histidine. It is broken down outside cells by diamine oxidase (DAO) and inside cells by histamine N-methyltransferase.

Low histamine – what does it mean?

A low value in stool is the normal case: the gut bacteria make little histamine, and what comes from food or from mast cells in the lining is broken down promptly by DAO. Only a little histamine then acts on the gut lining and gut muscles.

Raised histamine – what happens in the body?

When there is a lot of histamine in the gut, it first acts locally: via H1 and H2 receptors it stimulates the gut muscles and the release of fluid into the gut – cramps, bloating and diarrhoea may follow – and the vessels of the lining become more permeable. If DAO's breakdown capacity is not sufficient, some of the histamine passes through the gut wall into the blood and acts there on vessels, skin and heart: headaches, skin flushing, itching, a blocked nose and palpitations are possible. Raised values arise when histamine-producing bacteria are more numerous in the gut, with a lot of histamine from food, when mast cells in the lining release more histamine – for example with inflammation or allergic reactions – or when little DAO is produced.

The interpretation is given in your report.