Threonine has a mild glucose-sparing effect and is a precursor of amino acids glycine and serine. Threonine is one of the immune-stimulating nutrients (cysteine, lysine, alanine, and aspartic acid are others), as it promotes thymus growth and activity. A deficiency of threonine in rats has been associated with a weakened cellular response and antibody formation. One gram of threonine twice daily may also be helpful in some cases of depression.