Homocysteine

Homocysteine (pronounced homo-SIS-teen) is an amino acid and is found normally in the body. Its metabolism is linked to that of several vitamins, especially folic acid, B6, and B12. Deficiencies of those vitamins may cause elevated levels of Homocysteine.

 

Homocysteine is a building block for the production of proteins in the body. However, elevated levels of Homocysteine are associated with premature vascular disease. Studies have shown that increased homocysteine levels can dramatically increase your risk of heart disease, stroke, peripheral vascular disease and clotting disorders. Fortunately, high homocysteine levels may be reduced with dietary vitamins folate, B6 and B12. High homocysteine levels are seen in renal disease, heart failure, and B12 or folate deficiency. Homocysteine levels also tend to increase with age. Low levels are associated with diets high in fruits and vegetables (especially those high in B vitamin and folate). An ideal homocysteine levels is less than 9 micromol/liter.

In recent years, studies have accumulated suggesting that a high level of homocysteine increases a person’s chance of developing heart disease, stroke, and peripheral vascular disease (a reduced blood flow to the hands and feet).

In September 1995, the National Heart, Lung, and Blood Institute (NHLBI) convened a special panel to review the scientific evidence about homocysteine’s possible link to heart disease. The information that follows is based on the panel’s conclusions.

Briefly, the panel said that an elevated homocysteine level appears to increase the risk of heart disease, stroke, and peripheral vascular disease. However, no studies have been done to show that lowering the homocysteine level reduces the risk of heart disease. The panel stressed that more research, especially a clinical trial, must be done to understand the possible association between the level of homocysteine and heart and related diseases.

Homocysteine & Heart Disease

Various studies have found that persons with elevated levels of homocysteine in their blood are at an increased risk of heart and vessel disease. These studies include the Physicians’ Health Study, the Tromso Study from Norway, the Framingham Heart Study, and a meta-analysis of nearly 40 studies. Some studies indicate that persons with elevated homocysteine levels tend to also have other risk factors for heart disease, especially smoking, high blood pressure, and high blood cholesterol.

So far, no clinical trial has been done to show that lowering homocysteine levels alters the progression of heart disease, or prevents heart attacks or strokes.

Why Homocysteine?

Much more basic research must be done before scientists understand how an elevated homocysteine level affects the development and progression of heart disease. However, scientists have several theories: First, a high level of homocysteine may be involved with the process called atherosclerosis, the gradual buildup of fatty substances in arteries.

Homocysteine also may make blood more likely to clot by increasing the stickiness of blood platelets. Clots can block blood flow, causing a heart attack or stroke. Increased homocysteine may affect other substances involved in clotting too. Finally, higher homocysteine levels may make blood vessels less flexible–and so less able to widen to increase blood flow. However, none of theories has so far been proven.

What Determines Homocysteine Levels?

Individuals differ in their levels of homocysteine. Two key factors affect a person’s homocysteine level–genetics and environment.

Genetics

Genetic factors help regulate the level of homocysteine in the blood. For instance, genetic flaws (mutations) can affect homocysteine’s metabolism. 

The NHLBI Family Heart Study found families with genetic mutations in the enzymes involved in homocysteine metabolism.The NHLBI Framingham Heart Study and other investigations have found a relationship between elevated homocysteine levels and families with early heart disease.

Environment

The level of homocysteine in the blood also is affected by the consumption of vitamins, especially folic acid, B6, and B12.

Data from the Framingham Heart Study show that only 30-40 percent of the population was getting 200 or more micrograms of folic acid in their diet. The data indicated that for many persons an intake of at least 400 micrograms was needed to keep homocysteine levels from becoming elevated.

Data also indicate that homocysteine levels are higher in older persons than younger ones and in women after menopause than in those before. But more research is needed to confirm and explain these differences.