How can the body make niacin from tryptophan?

The human body synthesizes niacin from the amino acid tryptophan through specific metabolic pathways.12

This conversion occurs in two primary ways:

• Metabolic Synthesis: Under normal physiological conditions, the body utilizes tryptophan as a precursor to manufacture niacin. This internal synthesis is a critical biological process that helps maintain adequate levels of the vitamin, which is essential for preventing pellagra.123
• Intestinal Bacterial Action: In the intestinal tract, bacteria can convert dietary tryptophan into niacin, providing an additional source of the vitamin for the body.3

Because of this relationship, foods rich in protein—which contain tryptophan—can help prevent or cure pellagra even if they are poor direct sources of niacin itself. Conversely, conditions that interfere with the absorption or transport of tryptophan, such as Hartnup disease, can limit the body's ability to synthesize sufficient niacin, potentially leading to deficiency symptoms.31