Do B vitamins support one-carbon metabolism and methylation capacity?

One-carbon metabolism is a vital biochemical network regulating cellular methylation, nucleotide synthesis, and redox balance—pathways of particular importance for maintaining cellular health during aging.

Mechanistic pathway modulation

• Coenzyme and substrate support: Folate (vitamin B9) acts as the primary carrier of one-carbon units, directly supplying 5-methyltetrahydrofolate (5-MTHF). Vitamin B12 (cobalamin) serves as an essential cofactor for methionine synthase, which transfers the methyl group from 5-MTHF to homocysteine, producing methionine.
• Enzymatic cofactors: Riboflavin (vitamin B2) is the precursor for flavin adenine dinucleotide (FAD), a mandatory cofactor for methylenetetrahydrofolate reductase (MTHFR) activity. Vitamin B6 (pyridoxal 5'-phosphate) directs the transsulfuration of homocysteine into cysteine, sustaining overall pathway flux.

Homocysteine and methylation capacity

• SAM/SAH ratio maintenance: Methionine generated through this vitamin-dependent network is converted into S-adenosylmethionine (SAM), the universal methyl donor for DNA, RNA, proteins, and lipids.
• Inhibition of methyltransferases: Insufficient B vitamin levels impair homocysteine remethylation, leading to an accumulation of S-adenosylhomocysteine (SAH). Because SAH acts as a potent, competitive inhibitor of DNA methyltransferases, a depleted SAM/SAH ratio directly compromises cellular and epigenetic methylation capacity.

Bottom line

• Folate, vitamin B12, riboflavin, and vitamin B6 function as indispensable cofactors and substrates that directly sustain one-carbon flux, optimize the SAM/SAH ratio, and prevent homocysteine-induced suppression of cellular methylation capacity.