What Is Homocysteine?
Homocysteine is an amino acid your body makes when it breaks down methionine, a protein building block. Normally, your body quickly converts homocysteine into other substances using vitamin B12, folate, and vitamin B6.
When this process doesn't work well, homocysteine can build up in the blood.
Why High Homocysteine Matters
Elevated homocysteine is associated with:
- Higher risk of heart disease and stroke
- Blood clots
- Cognitive decline and dementia
- Pregnancy complications
It's worth noting that studies lowering homocysteine with B vitamins have shown mixed results for preventing heart attacks, though some trials suggest benefits for stroke risk and slowing brain shrinkage in certain people. Homocysteine is best viewed as a marker that may point to an underlying, fixable issue.
Common Causes of High Homocysteine
- Low vitamin B12 (common with age, vegetarian or vegan diets, and medications like metformin or acid reducers)
- Low folate
- Low vitamin B6
- Kidney disease
- Hypothyroidism
- Heavy alcohol use and smoking
- Certain medications
- Genetic factors, including MTHFR variants
What Is MTHFR?
MTHFR is a gene that makes an enzyme involved in processing folate. Common variants—especially C677T—can reduce the enzyme's activity. These variants are very common: a large share of people carry at least one copy.
Having an MTHFR variant doesn't automatically mean you'll have high homocysteine or health problems. It mainly matters if your folate intake is low. Major medical organizations generally don't recommend routine MTHFR testing, because homocysteine and B vitamin levels are more useful to act on.
How to Lower Homocysteine
- Make sure you're getting enough folate (leafy greens, beans, lentils), B12 (meat, fish, eggs, dairy, or supplements), and B6
- Correct any B12 deficiency
- Limit alcohol and stop smoking
- Address thyroid or kidney issues
Supplements should be guided by your lab results and a provider.
Learn more about lab testing here: Heva Lab Testing
The Bottom Line
High homocysteine often points to low B vitamins and is linked to heart and brain health risks. MTHFR variants are common and only one possible factor—testing and correcting nutrient levels is usually the most useful next step.