Homocysteine

*This risk factor is not yet fully established. While it has been shown to be associated with heart disease and heart attacks, it has not yet been shown that altering levels will translate into fewer heart attacks or deaths.

What is homocysteine and how is it measured?

Homocysteine is a chemical found in the blood that is produced when the amino acid methionine (a building block for proteins) is broken down. High levels are linked to an increased risk of heart disease. Homocysteine is measured through a routine blood test. The homocysteine test is not widely available, costs about $100, and is not currently covered by insurance. More rarely, your healthcare provider may order a methionine-load test, which measures homocysteine before and after you swallow 100 mg/kg of methionine (dissolved in orange juice). This test can diagnose homocysteine abnormalities in people at high risk for heart disease who have normal homocysteine levels when tested with the routine blood test.

Homocysteine testing may be useful if you or a family member have heart or blood vessel disease, but do not have any of the well-established risk factors such as smoking, high blood cholesterol, high blood pressure, obesity, or diabetes.

AHA Fasting Blood Homocysteine Levels
Normal 5 to 15
Moderately High 16 to 30
Intermediately High 31 to 100
Very High More than 100
Levels are measured in micromoles of homocysteine per liter of blood (µmol/L)

How does homocysteine affect heart disease risk?

People with high homocysteine levels have a higher risk of heart attack, stroke, and developing blood clots in the arteries and veins of the legs. One study found that among women with heart disease, those with high homocysteine levels were over 4 times more likely to die from heart disease than women with normal homocysteine levels. However, it is not yet clear whether high homocysteine levels cause these heart problems or if existing heart problems lead to high levels of homocysteine.

What causes high homocysteine levels?

Your diet and genetic makeup affect your homocysteine level. Folic acid and other B vitamins, such as B6 and B12, break down homocysteine in the body. If you do not get enough of these vitamins (see table below), this will raise homocysteine levels. However, it has not been shown that taking folic acid supplements or vitamins will reduce your risk of heart disease.

Some medical conditions can raise homocysteine levels, including kidney disease, low levels of thyroid hormones, and psoriasis (an immune disease that causes patches of inflamed, scaly skin), as can certain medications such as epilepsy drugs or methotrexate (used to treat arthritis).

In women, hormones also have an effect, and high levels of estrogen are associated with lower homocysteine levels. Premenopausal women have lower homocysteine levels than men of the same age, and pregnant women have lower homocysteine levels than women who are not pregnant and not using birth control pills. Postmenopausal women older than 55 taking estrogen have lower homocysteine levels compared with postmenopausal women not taking estrogen and men of the same age. However, taking estrogen does not decrease your risk of heart disease.

How are high homocysteine levels treated?

There is no treatment plan for high homocysteine levels, since it has yet to be shown that lowering homocysteine levels lowers the risk of heart attacks or heart disease. There are currently several ongoing studies to determine if folic acid and B vitamins can lower the risk of heart disease by lowering homocysteine. Some recent studies have not shown a benefit, but this may be because the trials were not large enough or did not reduce homocysteine enough. Even so, if you are at high risk for heart disease you are strongly advised to get enough folic acid in your diet by eating at least 5 servings of fruits and green, leafy vegetables daily. If you are at high risk for heart disease and have had a homocysteine test that showed high levels, you may be advised to take vitamin supplements containing folic acid, vitamin B12, and vitamin B6.

There are some hearty-healthy lifestyle choices that may also lower homocysteine levels, such as the DASH Diet (Dietary Approaches to Stop Hypertension). In addition, stress management, moderating caffeine and alcohol intake, and quitting smoking may lower homocysteine.

Micronutrient

Recommended Daily Allowance

Good Sources

Vitamin B6

1.3 – 1.7 mg

Beef, chicken, milk, tuna, potatoes, corn, bananas, watermelon, avocados, pork, fatty fish, sunflower seeds, soybeans, wheat germ, and fortified cereals

Vitamin B12

2.4 µg

Fortified cereals, fish, liver, kidney, salmon, tuna, pork, eggs, beef, cheese, and chicken

Folic acid

400 µg (same for pregnant women*)

Citrus fruit, orange juice, beans, liver, green leafy vegetables (such as turnip greens, broccoli, or spinach), peas, chicken giblets, and nuts. Also, many breads, cereals, flours, pasta, and rice have been fortified with folic acid to add at least 100 micrograms of folic acid to a person’s daily diet

*Folic acid supplements are recommended for women who may become pregnant to prevent neural tube defects (such as spina bifida) in their babies

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