Histamine intolerance
Histamine intolerance, sometimes called histaminosis, is an over-accumulation of dietary histamine in the human body. Histamine intolerance is sometimes informally called an allergy; however, the intolerance is technically caused by the gradual accumulation of extracellular histamine due to an imbalance. Roughly 1% of the population has histamine intolerance; of those, 80% are middle-aged. General. The imbalance in histamine intolerance is between the synthesis and selective release of histamine from certain granulocytes (i.e., mast cells and basophils), versus the breakdown of histamine by the enzymes which metabolize it, such as diamine oxidase (DAO) and histamine N-methyltransferase  (HNMT). In contrast, allergic reactions involving an immediate allergic response to an allergen are caused by anaphylactic degranulation, which is the abrupt and explosive release of "pre-formed mediators", including histamine, from mast cells and basophils throughout the body. Symptoms. Possible symptoms after ingestion of histamine-rich food include: Metabolism. In the human body, histamine is metabolized extracellularly by the enzyme diamine oxidase (DAO), and intracellularly by histamine N-methyltransferase (HNMT) and aldehyde oxidases (AOX1). In histamine intolerance, the activity of DAO is limited, and histamine taken up by the diet and formed in the body is only partially metabolized . The consumption of histamine-containing food (e.g., red wine or hard cheese) leads to a pseudoallergic reaction. It is unclear how histamine passes through the intestinal wall during absorption and enters the blood without coming into contact with the aldehyde oxidases expressed in intestinal cells and histamine N-methyltransferases. Potentially harmful foods. The following food categories have been quoted in literature as histamine rich: Tobacco. Active or passive exposure to tobacco smoke is suspected of favouring histamine intolerance, but has not been adequately studied. Other. (This list is drawn from the German Wikipedia article on histamine intolerance. It has been  further expanded using Verträglichkeit von histaminhaltigen Lebensmitteln (PDF; 28 kB)). Diagnosis. For a diagnosis, the case history is essential. However, since many complaints such as headaches, migraines, bronchial asthma, hypotension, arrhythmia and dysmenorrhea (painful periods) may be caused by something other than histamine intolerance, it is not surprising that half of suspected diagnoses are not confirmed. The diagnosis is usually made by intentionally provoking a reaction. However, since histamine can potentially cause life-threatening conditions, the following procedure is preferred: take blood samples before and after a 14-day diet, and measure changes in histamine and diamine oxidase (DAO) levels . Rather than increase histamine during the test diet, eliminate it. This procedure does not endanger the patient. Quite the contrary: in the presence of histamine intolerance, the symptoms have improved or disappeared completely. At the same time, the histamine blood level halves and the DAO increases significantly. If there is no histamine intolerance, the blood levels do not change and neither do the symptoms. Simultaneously, food allergy, cross-reactions with pollen, fructose malabsorption, lactose intolerance, and celiac disease should be excluded. Therapy. The basis of treatment is a reduction of the dietary histamine through a histamine-poor diet. Certain foods  (e.g., citrus fruits) and certain medicines (e.g., morphine) which do not contain histamine per se are also to be avoided, because they are known to release histamine stored in the body (histamine liberation). If eating histamine-containing foods is unavoidable, antihistamines and cromolyn sodium may be effective. The intake of diaminoxidase (DAO) in capsule form with meals may reduce the symptoms of histamine intolerance. In cases of high blood glutamate, such as can occur in some cases of eczema and histamine intolerance, Reinhart Jarisch recommends vitamin B6 treatment. This promotes the body's own synthesis of DAO and thus fights  the effects of histamine intolerance. The reference ranges (normal values) for blood glutamic acid are 20–107 in infants, 18–65 in children and 28-92 μmol / ml in adults.