One-carbon metabolism

One-carbon metabolism is an interconnected network of folate and methionine cycles that transfers single-carbon units for the biosynthesis of nucleotides, the remethylation of homocysteine to methionine, and the production of S-adenosylmethionine (SAM), the universal methyl donor for DNA, RNA, histone, and lipid methylation. Dietary inputs — including folate, choline, betaine, methionine, vitamins B2, B6, and B12 — feed the network at multiple entry points, making its output sensitive to nutritional status. With ageing, dysregulation of one-carbon flux is associated with elevated plasma homocysteine, global DNA hypomethylation, and impaired epigenetic maintenance, linking the pathway mechanistically to two recognised hallmarks of ageing: epigenetic alterations and genomic instability.