Metabolic

Homocysteine

Homocysteine is an amino acid produced as a byproduct of methionine metabolism. It is not obtained from diet but is generated internally and must be recycled back to methionine (via B12 and folate) or converted to cysteine (via B6). When this recycling pathway is impaired — by nutrient deficiency or genetic variants like MTHFR — homocysteine accumulates in the blood.

Optimal Ranges

Clinical (NHS) Range

<15 µmol/L

µmol/L

Performance-Optimised Range

<8 µmol/L

µmol/L

The clinical range defines what is considered medically “normal” — broad enough to cover 95% of the population. The performance range reflects where research and clinical experience suggest most people feel and function at their best.

Why It Matters

Why Homocysteine matters for performance

Elevated homocysteine is an independent risk factor for cardiovascular disease, stroke, blood clots, and cognitive decline. It damages the endothelium (arterial lining), promotes oxidative stress, and impairs nitric oxide production — reducing blood flow and exercise performance. Critically, homocysteine is a functional marker of B12, folate, and B6 status — elevated levels often indicate deficiency in one or more of these vitamins even when serum levels appear 'normal'. It's particularly important for men with the MTHFR C677T variant (~40% of the population), who have impaired folate metabolism and tend to run higher homocysteine.

Symptoms

Signs your levels may be off

Low / Deficiency

  • Low homocysteine is not a concern — lower is better

High / Excess

  • Often asymptomatic until cardiovascular event
  • Fatigue and brain fog (due to underlying B vitamin deficiency)
  • Blood clots (deep vein thrombosis)
  • Early cognitive decline
  • Poor exercise recovery

Dietary Sources

Foods that support Homocysteine levels

Leafy greens rich in folate — spinach, kale, broccoliAnimal protein for B12 — meat, fish, eggs, dairyLegumes — lentils, chickpeas (folate + B6)Fortified cereals and nutritional yeastBetaine-rich foods — beets, quinoa, spinach

Supplementation

Evidence-based supplementation

The homocysteine-lowering protocol is well-established: methylfolate (5-MTHF, 800mcg-5mg daily), methylcobalamin (B12, 1,000mcg daily), and pyridoxal 5'-phosphate (B6, 25-50mg daily). This combination addresses all three recycling pathways. Betaine (trimethylglycine, 500-3,000mg daily) provides an additional pathway for homocysteine conversion. For MTHFR carriers, methylated forms are essential — folic acid (synthetic) may not convert efficiently. Response is typically seen within 4-8 weeks. If homocysteine remains elevated despite supplementation, investigate kidney function (the kidneys are the primary excretion route).

Research

Key study

Homocysteine and cardiovascular disease: evidence on causality from a meta-analysis

Wald DS, Law M, Morris JK

BMJ (2002)

DOI: 10.1136/bmj.325.7374.1202

Related Biomarkers

Vitamins & Minerals

Vitamin B12 (Cobalamin)

Optimal: 500-800 pg/mL

Vitamins & Minerals

Folate (Vitamin B9)

Optimal: 20-45 nmol/L

Vitamins & Minerals

Vitamin B6 (Pyridoxine)

Optimal: 50-125 nmol/L

Related Guides

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Complete Guide to Blood Tests

What to test and why it matters

Test your Homocysteine levels

Homocysteine is included in the Helvy 50+ biomarker panel. Get your results in 5 days with a personalised protocol.

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This content is for educational purposes only and does not constitute medical advice. Your data suggests areas for optimisation, but any concerns should be discussed with a qualified healthcare professional. If your results flag values outside safe ranges, we recommend consulting your GP.