Histidine is a semiessential amino acid, which means your body normally makes as much as it needs. Like most other amino acids, histidine is used to make proteins and enzymes. The body also uses histidine to make histamine, the culprit behind the swelling and itching you feel in an allergic reaction.

It appears that people with rheumatoid arthritis may have low levels of histidine in their blood. This has led to some speculation that histidine supplements might be a good treatment for this kind of arthritis, but so far no studies have confirmed this.

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Sources  

Although histidine is not required in the diet, histidine deficiencies can occur during periods of very rapid growth. Dairy products, meat, poultry, fish, and other protein-rich foods are good sources of histidine.

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Therapeutic Dosages  

A typical therapeutic dosage of histidine is 4 to 5 g daily.

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Therapeutic Uses  

Although individuals with rheumatoid arthritis appear to have reduced levels of histidine in the blood, 1,2 this by itself doesn't prove that taking histidine will help. One study designed to evaluate this question directly found no significant benefit. 3

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Safety Issues  

As a necessary nutrient, histidine is believed to be safe. However, maximum safe dosages of histidine have not been determined for young children, pregnant or nursing women, or those with severe liver or kidney disease. As with other supplements taken in large doses, it is important to purchase a quality product, as contaminants present even in very small percentages could conceivably add up and become toxic.