Homocysteine
Amino acid intermediate as vascular and cognition marker
Also known as
Definition
Homocysteine is a sulfur-containing amino acid derived from methionine metabolism, broken down by folate, vitamin B6, and vitamin B12. Elevated levels are an independent risk factor for heart disease, dementia, and stroke. Particularly relevant for vegans and individuals with MTHFR polymorphisms, who are prone to hyperhomocysteinemia.
| Parameter | Value |
|---|---|
| Unit | µmol/l |
| Reference Range | < 15 µmol/l (general) |
| Optimal Range (lab2go) | < 10 µmol/l (lab2go Optimum Zone) |
↓ What a low value means
Low homocysteine (< 7 µmol/l) is clinically unremarkable and considered advantageous. Extremely low values are not clinically relevant and require no intervention. Very low homocysteine indicates adequate B-vitamin supply and healthy methionine metabolism.
↑ What a high value means
Homocysteine 10–15 µmol/l: moderate hyperhomocysteinemia, elevated cardiovascular and neuronal risk. Above 15 µmol/l: hyperhomocysteinemia (independent risk factor for atherosclerosis, dementia, stroke). Above 30 µmol/l: severe hyperhomocysteinemia (rare, often genetic from CBS or MTHFR defects). Causes: folate, B12, and B6 deficiency (common in vegans), MTHFR C677T polymorphism, kidney insufficiency, hypothyroidism, certain medications (methotrexate, metformin).
✓ How to optimize this marker
Supplementation: methylfolate (active form, 400–800 µg/day), methylcobalamin B12 (500–1,000 µg/day), pyridoxal-5-phosphate B6 (10–25 mg/day). Prefer active forms, especially with MTHFR polymorphism. With metformin therapy: B12 supplementation important (metformin inhibits B12 absorption). Avoid heavy alcohol and smoking. Follow-up after 3 months.
When to test
Fasting measurement preferred (meals transiently raise homocysteine). Useful as a supplement to cardiovascular screening and dementia prevention. Screening for vegans, MTHFR polymorphism carriers, after stroke, with dementia risk, under metformin or methotrexate. Follow-up after B-vitamin supplementation after 3 months.
Frequently asked questions
What is the MTHFR polymorphism and how does it relate to homocysteine? +
MTHFR (methylenetetrahydrofolate reductase) is an enzyme that converts folic acid to its active form (methylfolate). The common C677T variant reduces enzyme activity by 30–70%, making homocysteine detoxification more difficult. Those affected benefit particularly from methylfolate rather than folic acid.
Does B-vitamin supplementation lower heart attack risk with high homocysteine? +
B vitamins reliably lower homocysteine, but direct evidence of cardiovascular risk reduction through supplementation (without deficiency) is inconsistent in RCTs. Evidence for brain health and dementia prevention is stronger (VITACOG trial).
Do I need to fast for homocysteine testing? +
Preferably yes — a protein-rich meal can transiently raise homocysteine. For optimal comparability, measure after 8–12 hours without food. If fasting is not possible, interpret the result accordingly.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.