Editing Niacin (section)

===Biosynthesis===
[[Image:Tryptophan metabolism.svg|thumb|300px|class=skin-invert-image|Niacin, [[serotonin]] (5-hydroxytryptamine), and [[melatonin]] [[biosynthesis]] from [[tryptophan]]]]
In addition to absorbing niacin from diet, niacin can be synthesized from the [[Essential amino acid|essential]] [[amino acid]] [[tryptophan]], a five-step process with the penultimate compound being [[quinolinic acid]] (see figure). Some bacteria and plants utilize [[aspartic acid]] in a pathway that also goes to quinolinic acid.<ref>{{cite journal |vauthors=Foster JW, Moat AG |title= Nicotinamide adenine dinucleotide biosynthesis and pyridine nucleotide cycle metabolism in microbial systems |journal= Microbiol. Rev. |volume= 44 |issue= 1 |pages= 83–105 |date= 1 March 1980 |doi= 10.1128/MMBR.44.1.83-105.1980 |pmid= 6997723 |pmc= 373235}}</ref> For humans, the efficiency of conversion is estimated as requiring 60{{nbsp}}[[gram#SI multiples|mg]] of tryptophan to make 1{{nbsp}}mg of niacin. [[Riboflavin]], [[Vitamin B6|vitamin B<sub>6</sub>]] and [[iron]] are required for the process.<ref name=PKIN2020Niacin /> Pellagra is a consequence of a corn-dominant diet because the niacin in corn is poorly bioavailable and corn proteins are low in tryptophan compared to wheat and rice proteins.<ref name=Carpenter1983>{{cite book |doi=10.1007/978-3-0348-6540-1_12 |chapter=The Relationship of Pellagra to Corn and the Low Availability of Niacin in Cereals |title=Nutritional Adequacy, Nutrient Availability and Needs |series=Experientia Supplementum |year=1983 | vauthors = Carpenter KJ |volume=44 |pages=197–222 |pmid=6357846 |isbn=978-3-0348-6542-5 }}</ref>