Homocysteine
Also reported as: tHcy · Total homocysteine
A sulphur-containing amino acid produced in methionine metabolism, cleared by pathways requiring folate, B12 and B6.
Upper bounds of 15 µmol/L are common but sit well above where risk begins to rise.
Risk associations begin below the typical laboratory ceiling; under 9 µmol/L is the usual preventive target, and the cognitive-decline data suggest under 10 matters most.
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Where the thresholds sit
| Band | Range (µmol/L) | Note |
|---|---|---|
| Optimal | 5–9 | — |
| Acceptable | 9–12 | — |
| Borderline | 12–15 | — |
| Elevated | > 15 | — |
Why it matters
Elevated homocysteine is consistently associated with cardiovascular events and, more strongly, with brain atrophy and cognitive decline. The honest caveat is that lowering it with B vitamins has not reduced cardiovascular events in trials — but the VITACOG trial did show slowed brain atrophy in people with elevated homocysteine and adequate omega-3 status.
What raises it
- Folate, B12 or B6 deficiency
- MTHFR variants, modestly
- Kidney impairment
- Hypothyroidism
- Metformin, through B12 depletion
- Heavy coffee and alcohol intake
What lowers it
- Folate, B12 and B6 repletion
- Riboflavin, in people with MTHFR variants
- Betaine (trimethylglycine)
How to move it
- 1Check B12 and folate before supplementing anything — deficiency is the usual cause and is worth identifying rather than masking.
- 2If you take metformin, have B12 checked; depletion is common and often missed.
- 3Where supplementation is needed, methylated forms are reasonable but not essential for most people.
- 4Do not treat an isolated mildly elevated homocysteine as a cardiovascular emergency. The trial evidence for lowering it does not support that.
What moves this marker
Interventions on this site with evidence behind them for this specific marker. None of them replaces working out why yours is where it is.
What makes a single reading misleading
- Samples must be separated promptly — delayed processing falsely raises the result.
- B-vitamin supplementation lowers the number reliably but has not lowered cardiovascular events in randomised trials.
- Kidney function strongly influences the level.
Sources
Read next
Educational only. Reference ranges are not diagnostic thresholds and this page cannot account for your medical history, medication or symptoms. Discuss any result that concerns you with a qualified clinician. See our medical disclaimer.