Tryptophan is the precursor of niacin and serotonin (vasoconstrictor and neurotransmitter). Low serotonin is often associated with disturbed sleep cycle or insomnia, anxiety or depression, aggressive behavior and low pain threshold. Tryptophan can be low as a result of low quality/quantity protein intake or intestinal malabsorption (eg. hypochlorhydria). Bacterial action on unabsorbed tryptophan in the intestine produces elevated levels of mildly toxic indole compounds such as indican (”blue diaper syndrome” in infants). A Comprehensive Stool Analysis may be warranted if dietary intake of protein appears to be adequate. Foods that are good sources of tryptophan include turkey, wild game, pork, soy protein, sunflower seeds, and cheeses.

This elevation of tryptophan suggests lowered blood tryptophan and perhaps low serotonin. Blood plasma tryptophan may be measured by plasma amino acid analysis; serotonin should be measured in blood platelets. Symptoms consistent with tryptophan deficiency are mainly those of serotonin insufficiency and may include: insomnia, anxiety, enhanced response to external stimuli (light, sound), and abnormal food cravings.

- High levels may result from either excessive supplementation or poor metabolic utilization of tryptophan.

- Required nutrients for this process include niacin and vitamin B6.