L-histidine is one of the 10 essential amino acids for infants. Most lists of amino acids classify L-histidine as an essential amino acid; however, it has never been clear if L-histidine is an essential amino acid for adults. Even though L-histidine is synthesized by the body, sufficient quantities may not be made to meet the physiological requirements imposed by certain stress or disease situations.
L-histidine plays a key role in production of red and white blood cells. It has been reported that rheumatoid arthritis sufferers have abnormally low blood levels of L-histidine. A pilot clinical study with RA patients show mixed results but still enough to warrant further research.