What is homocysteine?
Homocysteine is an amino acid that your body produces as a byproduct of processing methionine — another amino acid found in meat, fish, eggs, and dairy. In a healthy body, homocysteine gets quickly recycled into useful substances with the help of B vitamins. But when that recycling process doesn't work well, homocysteine builds up in your blood — and that's where the problems start.
Think of homocysteine like exhaust from an engine. A small amount is normal and gets cleared away. But if the exhaust system is clogged, the buildup damages everything around it.
Why it matters for longevity
Elevated homocysteine is a well-established risk factor for several serious health problems:
- Heart disease and stroke: High homocysteine damages the lining of blood vessels, promotes blood clots, and accelerates the buildup of plaque in arteries. Some researchers consider it an independent risk factor alongside cholesterol and .
- Cognitive decline: Elevated levels are linked to a higher risk of dementia and Alzheimer's disease. Studies show that people with high homocysteine experience faster brain shrinkage as they age.
- Bone health: High homocysteine weakens the collagen structure in bones, increasing the risk of fractures — particularly relevant for women after menopause.
The good news is that homocysteine is one of the most actionable biomarkers. In many cases, you can bring it down with targeted nutrition.
What the numbers mean
The conventional lab range for homocysteine is:
- Conventional range: 5–15 umol/L
However, most longevity-focused physicians aim for an optimal level of below 8 umol/L. Levels above 10 umol/L are increasingly associated with cardiovascular risk, and anything above 15 umol/L is considered clinically high and should be discussed with a doctor promptly.
What affects it
- B vitamin status: This is the biggest factor. Your body needs vitamin B6, vitamin B12, and folate (vitamin B9) to recycle homocysteine properly. If you're low in any of these, homocysteine rises.
- Diet: A diet low in leafy greens, legumes, eggs, and animal protein can leave you short on the B vitamins needed to keep homocysteine in check. Vegans and vegetarians are at higher risk for B12 deficiency in particular.
- Genetics (MTHFR): Some people carry a common gene variant called MTHFR that makes them less efficient at processing folate. This can lead to higher homocysteine levels even with a reasonable diet. If your homocysteine stays stubbornly high despite good nutrition, an MTHFR variant may be why. Supplementing with methylfolate (the active form of folate) instead of regular folic acid often helps.
- Kidney function: Your kidneys help clear homocysteine from the blood. Reduced kidney function can cause levels to rise.
- Age: Homocysteine tends to increase with age, partly because B vitamin absorption decreases over time.
- Women and pregnancy: Elevated homocysteine during pregnancy is linked to complications including preeclampsia, neural tube defects, and recurrent miscarriage. This is one reason prenatal vitamins include folate. Women planning to become pregnant should pay close attention to both folate status and homocysteine levels.
How to get tested
Homocysteine is a simple blood test that does not require fasting (though some labs prefer it). It's not always included in standard panels, so you may need to request it specifically. Online lab services like Quest or Ulta Lab Tests offer it directly. Testing once or twice a year is usually enough. If your level is high, retest after 2–3 months of targeted supplementation to see if it's responding.
How to improve it
- Get enough B12. Found in meat, fish, eggs, and dairy. If you eat a plant-based diet, supplementation is essential. Methylcobalamin is the preferred form for absorption.
- Get enough folate. Dark leafy greens (spinach, kale, romaine), lentils, chickpeas, and asparagus are excellent sources. If you have an MTHFR variant, look for methylfolate supplements rather than synthetic folic acid.
- Get enough B6. Found in poultry, fish, potatoes, bananas, and chickpeas. Most people get adequate B6 from a varied diet, but a B-complex supplement covers your bases.
- Consider a B-complex supplement. A quality B-complex that includes methylfolate, methylcobalamin (B12), and pyridoxal-5-phosphate (active B6) is often the simplest approach. This covers the three main nutrients your body needs to clear homocysteine.
- Eat a nutrient-dense diet. Beyond B vitamins, a diet rich in whole foods supports the many enzymatic processes involved in methionine metabolism. Check your overall nutrition balance with our Macro Calculator.
- Reduce alcohol intake. Alcohol interferes with B vitamin absorption and can raise homocysteine levels. Cutting back — or eliminating alcohol — is one of the quickest ways to help.