Homocysteine
Also known as: Hcy
What Does Homocysteine Measure?
Homocysteine is an amino acid naturally produced in the body as a byproduct of metabolizing methionine, an essential amino acid found in protein-rich foods. A blood homocysteine test measures the concentration of this compound circulating in your bloodstream. Unlike most amino acids, homocysteine is not obtained directly from food — it is created internally and must be properly broken down and recycled by the body using B vitamins (B6, B9/folate, and B12) as essential cofactors.
Why Does Homocysteine Matter?
Elevated homocysteine levels, a condition called hyperhomocysteinemia, are associated with increased risk of cardiovascular disease, stroke, blood clots, and cognitive decline including Alzheimer's disease. High homocysteine can damage the inner lining of blood vessels (endothelium), promote inflammation, and contribute to arterial plaque buildup. It is considered an independent risk factor for heart disease, meaning it raises risk even in people with otherwise normal cholesterol levels. Monitoring homocysteine provides an additional window into cardiovascular and neurological health that standard lipid panels may miss.
Normal Ranges
Males
5–15 µmol/L (optimal: below 10 µmol/L)
Females
5–12 µmol/L (optimal: below 10 µmol/L)
Children
3–10 µmol/L (varies by age and pubertal stage)
Causes of High Levels
- Deficiency in B vitamins (B6, B12, and folate/B9), which are essential for homocysteine metabolism
- MTHFR gene mutations that impair the body's ability to convert folate into its active form, reducing homocysteine clearance
- Chronic kidney disease, which reduces the kidneys' ability to filter and excrete homocysteine
- Hypothyroidism (underactive thyroid), which slows metabolic processing of homocysteine
- Excessive alcohol, smoking, and coffee consumption, which deplete B vitamins and impair metabolism
- Certain medications including methotrexate, metformin, proton pump inhibitors, and anticonvulsants that interfere with B vitamin absorption or function
Causes of Low Levels
- High dietary intake of folate, B6, and B12 through food or supplementation
- Following a plant-forward diet naturally rich in folate (leafy greens, legumes)
How to Improve Your Homocysteine
Diet
- Increase folate-rich foods such as leafy greens (spinach, kale, romaine), lentils, chickpeas, asparagus, and broccoli daily
- Eat B12-rich foods regularly including eggs, salmon, sardines, beef liver, dairy products, or fortified foods (especially important for vegetarians/vegans)
- Include B6 sources such as poultry, tuna, potatoes, bananas, and sunflower seeds in daily meals
- Reduce alcohol consumption, as alcohol depletes folate and B vitamins critical for homocysteine metabolism
- Limit excessive red meat and processed meat intake, as high methionine loads can increase homocysteine production if B vitamins are insufficient
Supplements
- Methylfolate (5-MTHF) 400–800 mcg/day, the active form of folate that bypasses MTHFR gene mutations
- Methylcobalamin (active B12) 500–1000 mcg/day, particularly important for older adults and vegans
- Pyridoxine or Pyridoxal-5-Phosphate (active B6) 25–50 mg/day to support homocysteine transsulfuration
- Betaine (trimethylglycine/TMG) 500–3000 mg/day, which provides an alternative methylation pathway to lower homocysteine
- Riboflavin (B2) 1.6–2 mg/day, important for activating MTHFR enzyme activity, especially in those with MTHFR variants
Related Biomarkers
Frequently Asked Questions
What level of homocysteine is considered dangerous?
Homocysteine above 15 µmol/L is generally considered elevated (hyperhomocysteinemia). Levels of 15–30 µmol/L are classified as moderate, 30–100 µmol/L as intermediate, and above 100 µmol/L as severe — the latter often due to rare genetic disorders. Even mildly elevated levels (10–15 µmol/L) are associated with increased cardiovascular and cognitive risk, which is why many integrative medicine practitioners aim for levels below 10 µmol/L for optimal health.
Can high homocysteine cause heart disease even if my cholesterol is normal?
Yes. Homocysteine is considered an independent cardiovascular risk factor, meaning elevated levels can damage arteries and increase heart disease risk even when cholesterol levels are perfectly normal. Homocysteine injures the endothelial lining of blood vessels, promotes oxidative stress, and contributes to platelet aggregation and clot formation. This is why measuring homocysteine provides important additional information that a standard lipid panel alone cannot capture.
Does the MTHFR gene mutation cause high homocysteine?
Yes, in many cases. The MTHFR gene produces an enzyme that converts dietary folate into its active form (5-methyltetrahydrofolate), which is essential for recycling homocysteine. Common MTHFR variants — particularly C677T — reduce this enzyme's efficiency by 30–70%, impairing homocysteine clearance. People with these variants often benefit from taking methylfolate (5-MTHF) instead of regular folic acid, combined with methylcobalamin (active B12) and sometimes B6. Genetic testing can identify whether you carry these variants.