'''Homocistein''' je neproteinska [[aminokiselina]]. On je homolog aminokiseline [[cistein]]a, od koje se razlikuje po dodatnoj [[metilen]]skoj (--{CH}-<sub>2</sub>-) grupi. On se biosintetiše iz [[metionin]]a uklanjanjem terminalne -{C}-<sup>ε</sup> metil grupe. Homocistein se može reciklisati u metionin ili konvertovati u cistein uz pomoć B-vitamina.
Detekcija visokih nivoa homocisteina je povezana sa kardiovaskularnim bolesima, mada snižavanje nivoa homocisteina ne poboljšava ishod oboljenja.<ref>{{cite journal |author=Martí-Carvajal AJ, Solà I, Lathyris D, Salanti G |title=Homocysteine lowering interventions for preventing cardiovascular events |journal=Cochrane Database Syst Rev |volume= |issue=4 |pages=CD006612 |year=2009 |pmid=19821378 |doi=10.1002/14651858.CD006612.pub2 |url= |editor1-last=Martí-Carvajal |editor1-first=Arturo J}}</ref> Povišeni novoi homocisteina su vezani za više stanja bolesti. Korisnost pokušaja snižavanja nivoa homocisteina je bilo nepotvršenanepotvrđena ili neubedljiva.<ref>{{cite journal|last=Martí-Carvajal|first=AJ|coauthors=Solà, I; Lathyris, D; Salanti, G.|title=Homocysteine lowering interventions for preventing cardiovascular events.|journal=Cochrane database of systematic reviews (Online)|date = 7. 10. 2009.|issue=4|pages=CD006612|pmid=19821378|doi=10.1002/14651858.CD006612.pub2}}</ref><ref>{{cite journal|last=Jardine|first=MJ|coauthors=Kang, A; Zoungas, S; Navaneethan, SD; Ninomiya, T; Nigwekar, SU; Gallagher, MP; Cass, A; Strippoli, G; Perkovic, V.|title=The effect of folic acid based homocysteine lowering on cardiovascular events in people with kidney disease: systematic review and meta-analysis.|journal=BMJ (Clinical research ed.)|date = 13. 6. 2012.|volume=344|pages=e3533|pmid=22695899|pmc=3374481}}</ref><ref>{{cite journal|last=Vizzardi|first=E|coauthors=Bonadei, I; Zanini, G; Frattini, S; Fiorina, C; Raddino, R; Dei Cas, L.|title=Homocysteine and heart failure: an overview.|journal=Recent patents on cardiovascular drug discovery|date=2009 Jan|volume=4|issue=1|pages=15–21|pmid=19149701}}</ref><ref>{{cite journal|last=Ahmadieh|first=H|coauthors=Arabi, A.|title=Vitamins and bone health: beyond calcium and vitamin D.|journal=Nutrition Reviews|date=2011 Oct|volume=69|issue=10|pages=584–98|pmid=21967159|doi=10.1111/j.1753-4887.2011.00372.x}}</ref>
