homocysteine

noun

ho·​mo·​cys·​te·​ine ˌhō-mō-ˈsi-stə-ˌēn  ˌhä- 

: an amino acid C₄H₉NO₂S that is produced in animal metabolism by the demethylation of methionine and that appears to be associated with an increased risk of cardiovascular disease when occurring at high levels in the blood

Examples of homocysteine in a Sentence

Recent Examples on the Web

Helps Protect Your Heart and Blood B12 helps break down homocysteine, an amino acid in the blood. —Jennifer Lefton, Verywell Health, 5 Nov. 2025

These vitamins lower homocysteine, a substance that can harm memory and thinking when levels get too high. —Brianna Tobritzhofer, Health, 28 Oct. 2025

There were perturbations in levels of omega-6 fatty acid, homocysteine, total protein, bilirubin and a host of other things. —Bruce Y. Lee, Forbes.com, 27 Apr. 2025

Word History

Etymology

International Scientific Vocabulary hom- + cysteine

First Known Use

1932, in the meaning defined above

Medical Definition

homocysteine

noun

ho·​mo·​cys·​te·​ine ˌhō-mō-ˈsis-tə-ˌēn  ˌhäm-ō- 

: an amino acid C₄H₉NO₂S that is produced in animal metabolism by the demethylation of methionine and forms a complex with serine that breaks up to produce cysteine and homoserine and that appears to be associated with an increased risk of cardiovascular disease when occurring at high levels in the blood