Histidine is one of 22 amino acids derived from foods with high protein content, as well as certain grains. It is one of the aromatic amino acids that start out being an essential amino acid in human infants, but then later become a non-essential amino acid as the body begins to synthesize it from imidazole, an organic compound and component of the aromatic ring in the acid’s chemical structure. Histidine is also a precursor of certain amines and amino acid peptides, such as histamine and carnosine. The full chemical name for this substance is written as 2-Amino-3-(1H-imidazol-4-yl)propanoic acid, but this is often abbreviated to L-histidine, His, or simply “H.”
Like other amino acids, histidine is found in virtually every cell in the body, and is involved in several biological functions. It is key to the formation of the myelin sheath, the protective barrier that surrounds neural cells and supports the transmission of brain signals to different parts of the body. It also participates in the detoxification of heavy metals and other cellular debris for elimination through the liver and kidneys. This substance is necessary in order for the body to manufacture both white and red blood cells. Finally, since this acid is involved in the production of histamine, it plays a role in making gastric enzymes needed for proper digestion, assisting the immune system in responding to the presence of allergens, and promoting normal sexual function.
L-histidine is required to enable the body to metabolize many trace minerals, including iron, zinc, copper, and manganese. For instance, in terms of iron utilization, it is needed to produce ferritin and "Fur," otherwise known as the iron storage protein and the iron uptake regulation protein, respectively. Histidine is also needed to produce a variety of enzymes, such as the antioxidant super oxide dismutase.
There is evidence to suggest that low levels of histidine, or impaired metabolism, may be linked to a variety of disorders. For example, researchers suspect that a deficiency may lead to an increased risk for the development of rheumatoid arthritis in some people. Abnormally low levels have also been linked to hearing loss following an injury due to specialized myelin sheath cells, called “Schwann cells,” failing to initiate the repair of damaged nerves. In contrast, high levels of this amino acid have been linked to a greater prevalence of depression and anxiety disorders, as well as schizophrenia.
While supplementation with this amino acid may benefit certain individuals, it is contraindicated in others. For one thing, its effects on the central nervous system and the regulation of histamine suggest that people with depressive disorders should avoid it unless otherwise directed by a physician. In addition, people with kidney or liver disorders should not take this amino acid in supplement form.