What Do High Homocysteine Levels Mean? (2025)

High homocysteine levels in the blood may indicate a deficiency in folic acid, vitamin B12, and vitamin B6, or can be caused by certain medications and health conditions. Elevated homocysteine may increase a person's risk of cardiovascular disease and cognitive decline, as well as neural tube defects in fetuses.

Homocysteine is an amino acid that can be measured with a blood test. High homocysteine levels may be treated with dietary changes and supplements.

What Homocysteine Is

Homocysteine is an amino acid. It is produced during the metabolism of another amino acid (methionine) during the digestion of protein.

Homocysteine is usually broken down quickly by essential B vitamins such as B12 (cobalamin), B6 (pyridoxine), and B9 (folic acid, the synthetic form of folate) to form other substances the body needs. However, when the metabolism of homocysteine is disrupted, high levels can accumulate in the blood.

Normal vs. High Levels

Homocysteine levels may differ among genders, but a value between 5 and 15 micromoles per liter (mcmol/L) is generally considered normal.

Levels that surpass 15 mcmol/L are called hyperhomocysteinemia. The levels of high homocysteine include:

• Moderate: 15–30 mcmol/L
  
• Intermediate: 31–100 mcmol/L
  
• Severe: 100 mcmol/L and higher

Risks

Hyperhomocysteinemia may damage the interior lining of the arteries. This increases the risk of blood clot formation, which can lead to heart attack, stroke, or other heart and blood vessel conditions.

Increased levels of homocysteine in the blood can also be a risk factor for health conditions in the following population groups:

• Pregnant people: During pregnancy, increased levels of homocysteine have been associated with an elevated risk of negative pregnancy outcomes. These include preeclampsia and intrauterine growth restriction (a condition in which a fetus does not grow as expected).
• Children: In children, high homocysteine levels are associated with cardiovascular disease, kidney disease, and obesity.
• Older adults: In people 65 or older, high homocysteine is linked to cardiovascular disease, neurodegenerative diseases, osteoporosis, and a decline in physical function.

Symptoms

There may be no signs when a person has high homocysteine levels. However, when these levels are elevated due to a vitamin B12 or folic acid deficiency, symptoms can range from mild to severe and include:

• Light-headedness
  
• Weakness
• Frequent headaches
• Heart palpitations
• Skin color or fingernail color changes
• Mouth sores
• Tingling or numbness in the extremities

Causes

Elevated homocysteine levels indicate a disturbance in the homocysteine metabolism process. This may be due to the following:

• Dietary deficiency: High homocysteine levels are most commonly seen in people who have a low intake of vitamin B12, vitamin B6, or folic acid. Eating foods rich in these vitamins can help your body break down homocysteine. Without them, homocysteine levels rise.
• Medications: Some drugs can cause an increase in homocysteine levels, including methotrexate (a disease-modifying antirheumatic drug used to treat inflammatory conditions), 6-azauridine (an antitumor medication), bile acid sequestrants (cholesterol-lowering medications) and some anticonvulsant medications.
• Health conditions: There may be a connection between some health conditions—such as osteoporosis, kidney disease, hypothyroidism, and Alzheimer's disease—and elevated homocysteine levels.
  

Diagnosis and Testing

A person's levels of homocysteine are measured with a blood sample. Your healthcare provider may recommend a homocysteine test if you are malnourished, are an older adult, or have a history of alcohol use or drug addiction.

A homocysteine test may also be used to:

• Check if a person has a deficiency in vitamins B6, B12, or folic acid
• Diagnose homocystinuria (a rare, genetic disease that may cause blood clots, weakened bones, and vision problems)
• Understand a person's risk for heart attack or stroke if they have a condition such as diabetes, high blood pressure, or high cholesterol

Treatments

Your healthcare provider will suggest how you should treat high homocysteine. Remedies include:

• Supplements: It's essential to maintain a balanced and healthy diet that provides your body with the necessary vitamins and minerals. However, if you're considering taking vitamin supplements, consult with your healthcare provider first to avoid any potential adverse effects.
• Dietary changes: Food high in folic acid and other B vitamins appears to help reduce high homocysteine levels. In a randomized trial of 65 participants with high homocysteine levels, daily consumption of folic acid supplements and folic acid–fortified breakfast cereals were found to be effective in reducing homocysteine levels.

Summary

High homocysteine levels may harm the interior lining of arteries, increase the risk of blood clots, and increase the chances of a heart attack, stroke, or other medical conditions. If you have high homocysteine levels, your healthcare provider may advise altering your diet.

Consuming a well-balanced diet may help provide the necessary vitamins in appropriate quantities. However, talk to your healthcare provider before taking vitamin supplements. Research has yet to definitively confirm whether lowering homocysteine levels can decrease the risk of heart attack or stroke.