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Am I HIT (Histamine Intolerant)?

Updated: Nov 23, 2017

Histamine intolerance (HIT) is caused by the imbalance of accumulation and degradation of histamine in the body manifesting in an allergy-like symptom such as hive, gastrointestinal symptoms, asthma, headache, migraine or even a chronic symptom such as fatigue, insomnia, anxiety and depression.





Histamine is known as a mediator of allergic reactions. It is released mainly by mast cells as an immediate inflammatory response to stimuli e.g. infection, insect bites, dust mites and toxic substances. Histamine also plays other roles in the body such as a neurotransmitter (a brain chemical that communicates information throughout our brain and body) and immunomodulator (a chemical affecting the immune function) depending on what receptors it binds to. There are four types of histamine receptors (designated H1-H4). Excess activation of H1 receptors triggers the symptoms of hay fever and other seasonal allergies. H2 receptors are found mainly on gastric parietal cells in the stomach lining and are responsible for stimulating the release of gastric acid. H3 receptors are present in the central nervous system affecting sleep and mood as well as regulating histamine in the body. H4 receptors regulate the levels of white blood cell released from bone marrow and direct mast cells.


Some people with allergies take antihistamines regularly to block histamine receptors however the common antihistamine drugs (e.g. fexofenadine) only target H1 receptor and is less effective for histamine-related symptoms involving other histamine receptors. When histamine excessively accumulates, the development of symptoms can be varied depending on histamine binding to corresponding receptors. These symptoms may include headache, migraine, diffuse pain of stomach, colic, flatulence, diarrhoea, rhinorrhoea (runny nose), nasal obstruction and in extreme cases even attack of bronchial asthma, bronchoconstriction, coughing, wheezing, chronic urticaria, dysmenorrhoea (painful period) and headaches connected with menstrual cycle. Mast cell degranulation and histamine release is the main mechanism for histamine overload, and in some patients with chronic idiopathic urticaria, this may be related to non-IgE food intolerance. Moreover, chemical and physical factors including stress, trauma, alcohol, and medications are responsible for histamine release.



Other chronic symptoms of HIT


Histamine and mast cell activation may play a crucial role in the pathogenesis of fibromyalgia. A study found a significant increase in mast cells (up to 14 times) in the papillary dermis of all fibromyalgia patients compared to healthy controls. The results reflect the mastocyte degranulation-related symptoms (e.g. fatigue, headache, abdominal