Which of the following has been shown to reduce plasma homocysteine concentrations?

• A. Vitamin E
• B. Folic acid
• C. L-carnitine
• D. Ascorbic acid

Answer: (B)

Folate status directly influences homocysteine metabolism. Homocysteine is remethylated back to methionine through a pathway that uses a folate-derived methyl donor, with vitamin B12 as a cofactor. When folate (folic acid) is available or supplemented, this remethylation works more efficiently, leading to lower levels of homocysteine in the plasma. The other nutrients listed do not have as consistent or robust evidence for lowering homocysteine; they have different roles (antioxidant effects, or other metabolic pathways) and don’t reliably reduce plasma homocysteine. Thus, folic acid is the intervention shown to reduce plasma homocysteine concentrations.