Définition
Homocysteine is an amino acid intermediate in the methylation cycle. Elevated levels signal impaired methylation, typically due to inadequate B vitamin status. It is an independent risk factor for cardiovascular events, cognitive decline, and accelerated biological aging — and one of the most correctable biomarkers available.
Homocysteine sits at a critical branch point in the one-carbon cycle. It can be converted back to methionine (requiring 5-MTHF and B12, or TMG through BHMT), or converted to cysteine through the transsulfuration pathway (requiring B6). When any of these clearance routes is impaired, homocysteine accumulates — making it one of the most sensitive functional markers of methylation status.
The clinical significance of elevated homocysteine is substantial. It is an independent risk factor for cardiovascular events (likely through endothelial damage and oxidative stress), cognitive decline (multiple trials have shown B vitamin lowering of homocysteine slows brain atrophy in older adults), and osteoporosis. Elevated homocysteine also signals reduced SAM availability for DNA methylation, which connects to epigenetic aging.
Target ranges matter. Conventional labs flag homocysteine only above 15 µmol/L, but longevity-oriented practice uses tighter targets: optimal is below 7 µmol/L, with intervention recommended above 8–9 µmol/L. Mild elevations (7–12 µmol/L) are extremely common and often correctable within weeks of B vitamin optimization.
The correction is straightforward. In order of typical priority: methylfolate (5-MTHF) if folate-deficient or MTHFR variant present; methylcobalamin (B12) if B12 is low or functional deficiency is suggested by elevated MMA; B6 (P5P) if elevated cystathionine suggests transsulfuration block; TMG if MTHFR variant makes BHMT pathway support valuable; adequate protein and choline to provide methyl donors. Most cases respond to a methylated B-complex within 4–8 weeks.
For women, homocysteine rises in perimenopause (estrogen supports methylation), during hormonal contraceptive use, and with age. It is a cornerstone biomarker of any methylation reset program and should be rechecked 8–12 weeks after starting methylation support.
Termes associés
Ava Longevity · Built on the Ava Method · MMXXV