5-hydroxytryptophan, or 5-HTP, is one of several byproducts arising from the metabolism of the amino acid L-tryptophan. L-tryptophan is an essential amino acid, meaning your body cannot synthesize it and it must be obtained from your food. This vital nutrient is needed for the synthesis of proteins, and it is the precursor for serotonin, melatonin and niacin. In order to efficiently convert L-tryptophan to these important compounds, your body also needs vitamin B-6, or pyridoxine.
Serotonin, a neurotransmitter that is synthesized in your brain, gut and liver, is the product of a two-step metabolic pathway that first converts L-tryptophan to 5-HTP and then converts 5-HTP to serotonin. The second step in this pathway is driven by an enzyme – amino acid decarboxylase – which requires vitamin B-6, in the form of pyridoxal-5-phosphate, as a cofactor. A 1995 "Journal of Neural Transmission" study demonstrated that supplementation with vitamin B-6 increased the conversion of 5-HTP to serotonin in primate animal models.
Amino acid decarboxylase deficiency is a rare genetic condition that results in a deficiency of serotonin and dopamine. This disorder causes abnormal movements and developmental delay in affected infants. In 2009, British researchers suggested that treatment with pyridoxal-5-phosphate, the active form of vitamin B-6, could improve the activity of amino acid decarboxylase and increase the conversion of 5-HTP to serotonin in children affected by this disease.
Your brain is protected from infections and toxins by an anatomical and physiologic envelope called the "blood-brain barrier." Serotonin produced in your intestine and liver is unable to enter your central nervous system because it cannot cross this barrier. However, L-tryptophan, 5-HTP and vitamin B-6 can all cross the blood-brain barrier, so your brain synthesizes its own serotonin using either L-tryptophan or 5-HTP as precursors and vitamin B-6 as the amino acid decarboxylase cofactor.
L-tryptophan, which is converted to 5-HTP in your body, is found in eggs, meats, dairy products and some nuts and seeds. L-tryptophan supplements are also available, and daily doses up to 3,000 mg are sometimes used for insomnia. Supplements containing up to 250 mg of 5-HTP are also commercially available. Daily requirements for vitamin B-6 vary from 100 mcg for infants to 2 mg for lactating females. Daily vitamin B-6 doses of 50 mg to 100 mg are commonly used without ill effects, as pyridoxine is a water-soluble B vitamin that is readily eliminated in your urine.
- “Journal of Neural Transmission”; Pyridoxine Effect on Synthesis Rate of Serotonin in the Monkey Brain Measured with Positron Emission Tomography; P. Hartvig, et al.; 1995
- “Molecular Genetics and Metabolism”; A New Perspective on the Treatment of L-Amino Acid Decarboxylase Deficiency; G.F.G. Allen, et al.; May 2009
- Office of Dietary Supplements: Vitamin B6