Homocysteine is an amino acid. Vitamins B12, B6 and folate break down homocysteine to create other chemicals your body needs. High homocysteine levels may mean you have a vitamin deficiency. Without treatment, elevated homocysteine increases your risks for dementia, heart disease and stroke.

What is homocysteine?

Homocysteine is an amino acid. Amino acids are chemicals in your blood that help create proteins. Vitamin B12, vitamin B6 and vitamin B9 (folate) break down homocysteine to generate other chemicals your body needs.


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What does homocysteine do?

When it interacts with the B vitamins, homocysteine converts to two substances:

  • Methionine, an essential amino acid and antioxidant that synthesizes (creates) proteins.
  • Cysteine, a nonessential amino acid synthesized from methionine that reduces inflammation, increases communication between immune cells and increases liver health.

What happens if I have too much homocysteine?

In a healthy person, homocysteine levels are around five to 15 micromoles per liter (mcmol/L). Nearly all that homocysteine converts to other proteins.

If you have more than 50 mcmol/L, the excess homocysteine may damage the lining of your arteries (blood vessels that carry oxygen-rich blood throughout your body). High levels of homocysteine can also lead to blood clots or blood vessel blockages. Artery damage or blood clots significantly raise your risk of heart attack.

Common Conditions & Disorders


What conditions and disorders affect homocysteine?

Typically, homocysteine breaks down into other substances, and only small amounts of homocysteine remain in your blood. Some conditions interfere with this process and leave you with high homocysteine levels.

You may have too much homocysteine in your blood if you have:

  • Deficiencies in vitamins B12, B6 or folate.
  • Heart disease.
  • Rare inherited diseases, such as homocystinuria (when your body can’t process methionine).

What are the risks of high homocysteine levels?

Without treatment, elevated homocysteine levels can lead to severe health complications. Too much homocysteine increases your risk for:


How do I know if I need a homocysteine test?

You may need a homocysteine test if you have a high risk of heart disease. You may also need a homocysteine blood test if you have symptoms of a vitamin B deficiency. Common symptoms of vitamin B deficiencies include:

  • Dizziness.
  • Fatigue.
  • Muscle weakness.
  • Pale complexion.
  • Tingling in your feet, arms or hands.
  • Tongue or mouth soreness.

What do the results of a homocysteine blood test mean?

Unusual homocysteine levels do not necessarily mean you have a medical condition. Other factors can affect your homocysteine blood levels, including:

Caring for Your Homocysteine Levels

How can I keep my homocysteine levels healthy?

If you have high homocysteine levels, your healthcare provider may recommend taking supplements of:

  • Vitamin B6.
  • Vitamin B12.
  • Folic acid (the human-made form of folate).

Increasing your vitamin intake alone does not reduce your risk of heart disease. You can lower your risk of heart disease by:

  • Avoiding or quitting smoking.
  • Consuming less than 2,300 milligrams of sodium daily.
  • Exercising at least three to five times weekly.
  • Managing your blood pressure.

When to Call a Doctor

What should I ask my doctor about homocysteine levels?

You may want to ask your healthcare provider:

  • What is the most likely cause of high homocysteine levels?
  • How can I lower my homocysteine?
  • How can I prevent my homocysteine levels from increasing again?
  • What are the risks of elevated homocysteine levels?

A note from Cleveland Clinic

Homocysteine is an amino acid. Vitamins B12, B6 and folate interact with homocysteine and create other proteins that your body needs. Typically, very little homocysteine stays in your blood. High homocysteine levels could mean you have an underlying condition such as heart disease or homocystinuria. Your healthcare provider may order a homocysteine blood test. Based on the test results, your healthcare provider can recommend the best treatment option.

Medically Reviewed

Last reviewed on 05/07/2021.

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