Year: 1999
Type: article
Abstract: Homocysteine and DietHomocysteine is a sulfur-containing amino acid, rapidly oxidized in plasma to the disulfides homocystine and cysteine-homocysteine (Figure 1).Plasma/serum total homocysteine, also termed homocyst(e)ine, is the sum of homocysteine in all 3 components.Figure 2 displays factors involved in the metabolism of homocysteine, including its metabolic relationship to methionine.Although dietary intake of total protein and methionine does not correlate significantly with blood homocyst(e)ine, 1 a single dose of oral methionine (100 mg/kg body weight) can elevate homocyst(e)ine levels, and as described further below, this has been used as a diagnostic test to detect disordered homocyst(e)ine metabolism.Because variable changes in homocyst(e)ine levels have been observed postprandially, 2 it is customary to obtain measurements in the fasting state.Normal levels of fasting plasma homocyst(e)ine are considered to be between 5 and 15 mol/L.Moderate, intermediate, and severe hyperhomocyst(e)inemia refer to concentrations between 16 and 30, between 31 and 100, and Ͼ100 mol/L, respectively.3 Several vitamins function as cofactors and substrates in the metabolism of methionine and homocysteine (Figure 2).Folic acid and cyanocobalamin (vitamin B 12 ) regulate metabolic pathways catalyzed by the enzymes methylenetetrahydrofolate reductase (MTHFR) and methionine synthase, respectively, whereas pyridoxine (vitamin B 6 ) is a cofactor for cystathionine -synthase.A number of studies have shown inverse relationships of blood homocyst(e)ine concentrations with plasma/serum levels of folic acid, vitamin B 6 , and vitamin B 12 .4 -6 Administration of supplemental folic acid in doses between 0.2 and 15 mg/d can lower plasma homocyst(e)ine levels without apparent toxicity.[7][8][9] On the basis of meta-analysis of 12 clinical studies, all but 1 of which was a placebo-References for this article may be found in the on-line version that appears on the American Heart Association Web site (http://www.americanheart.
Source: Circulation
Language: English
Subfield: Nutrition and Dietetics
Field: Nursing
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2050878161