Histidine

An essential amino acid, precursor of histamine. Important for the acid-base buffer in the blood (haemoglobin) and as a building block of carnosine in muscle.

What histidine does in the body

Histidine is an essential amino acid that the body cannot make itself. Its imidazole ring can easily take up and release hydrogen ions at the body's level of acidity. This is why histidine buffers acid in the blood within haemoglobin, and in muscle it forms carnosine together with beta-alanine, which captures the acid produced during exertion. In haemoglobin, a histidine holds the iron of the haem in place, and in many enzymes it binds zinc, copper or iron in the active centre. Histidine decarboxylase with vitamin B6 forms histamine from it – in mast cells for immune reactions, in the stomach lining for acid production and in the brain as a wakefulness signal. Histidine is broken down via urocanic acid to glutamate; folate is needed for the last step.

Low histidine – what happens in the body?

When little histidine is available, building material for haemoglobin and carnosine is lacking. Studies in people with chronic kidney disease have observed a link between low histidine and low haemoglobin, and in muscle the ability to buffer acid declines. Inflammatory processes are also associated with lower values: in studies they were lower in rheumatoid arthritis, chronic inflammatory bowel diseases and excess weight. Causes are low protein intake and increased consumption during inflammation.

High histidine – what does it mean?

A high value does not automatically mean more histamine: how much histamine is produced depends mainly on the activity of histidine decarboxylase in the cells and less on the histidine in the blood. Raised values arise when breakdown is slower – in the rare inherited condition histidinaemia, which usually causes no complaints, or when little folate is available for breakdown; the intermediate product FIGLU then also builds up. After protein-rich meals the value rises temporarily.

The interpretation is given in your report.