Définition
The one-carbon cycle is a network of interconnected biochemical pathways that transfer methyl groups for DNA methylation, neurotransmitter synthesis, homocysteine clearance, and phospholipid production. It is the foundation of methylation capacity — and one of the most nutritionally modifiable systems in the body.
The one-carbon cycle has three interlocking components: the folate cycle, the methionine cycle, and the transsulfuration pathway. The folate cycle converts dietary folate into 5-methyltetrahydrofolate (5-MTHF), the biologically active form. 5-MTHF donates its methyl group to convert homocysteine back into methionine, which is then activated to S-adenosylmethionine (SAM) — the universal methyl donor used in over 200 methylation reactions throughout the body.
After SAM donates its methyl group, it becomes S-adenosylhomocysteine (SAH), then homocysteine. Homocysteine has three possible fates: remethylation back to methionine (requiring 5-MTHF and B12), remethylation via betaine (TMG) through the BHMT pathway, or conversion to cysteine through the transsulfuration pathway (requiring vitamin B6). When any of these pathways is impaired, homocysteine accumulates — a marker of methylation insufficiency.
The key nutrient co-factors: methylfolate (5-MTHF, often supplemented directly rather than as folic acid to bypass MTHFR polymorphisms), methylcobalamin (B12), pyridoxal-5-phosphate (active B6), riboflavin (B2), choline, and betaine (TMG). Roughly 40% of people carry at least one MTHFR variant that reduces folate conversion efficiency — a genetic factor that amplifies the importance of active-form B vitamin intake.
For women, methylation supports estrogen metabolism. Estrogen is metabolized through methylation-dependent pathways in the liver, and impaired methylation can shift estrogen breakdown toward less favorable metabolites. This is why homocysteine, methylfolate status, and B12 status are core labs in any comprehensive women's longevity workup.
Termes associés
Ava Longevity · Built on the Ava Method · MMXXV