Homocysteine is an amino acid used to make proteins. Like other amino acids, small amounts normally circulate through the body in the blood stream. For many years, doctors have known that elevated blood levels of homocysteine are associated with an increased risk of heart attacks and strokes, the top and third leading causes of death in the United States.

The key question is will the reduction of homocysteine levels in the blood mean less chance of a heart attack and stroke? From a biologic standpoint this makes sense, but studies have not shown that lowering the homocysteine level makes a difference.

Diet Can Help

The good news is that homocysteine levels can often be managed with diet. Three nutrients in particular can help lower elevated homocysteine levels: folic acid, which is abundant in green leafy vegetables, oranges and fortified cereals; vitamin B-6, found in many foods, including bananas, potatoes and fortified cereals; and vitamin B-12, found only in animal products, such as meats, poultry, fish and eggs, as well as in fortified cereals. These nutrients are believed to help keep homocysteine in check by helping it convert into other substances in the blood that aren't associated with heart disease.

Some studies show that many people in general — not only those with elevated homocysteine levels — are not getting enough of these nutrients in their diet. The usual recommendation is to ingest at least 400 micrograms of folic acid each day — the amount found in a cup of many fortified cereals. You can also get that amount by consuming six asparagus spears, a cup of orange juice, a half cup of lentils and two slices of whole-wheat bread.

The recommended daily consumption for vitamin B-12 is 2.4 micrograms, the amount found in a chicken breast, a hard-boiled egg and a cup of yogurt. The daily recommended dose of vitamin B-6 is between 1.3 and 1.7 milligrams a day, which can be found a baked potato (with its skin) and a banana.

You may even want to take a multiple vitamin or a B-complex vitamin daily to be sure that you are getting enough folic acid, B-6 and B-12.

What's Normal?

Normal homocysteine levels range between one and 10 micromoles per liter. Unlike cholesterol, which is considered problematic when it rises above 200 milligrams per deciliter, researchers haven't set a "safe" level of homocysteine.

There is not enough evidence to indicate that widespread screening for elevated homocysteine levels is useful. However, people with family members who have angina or who had a heart attack at a young age may benefit from having a blood homocysteine test.

Homocysteine first came under suspicion 31 years ago when Harvard pathologist Kilmer McCully, M.D., discovered that children with severe arteriosclerosis (clogging of the arteries) also had high homocysteine levels. Dr. McCully speculated the substance may also play a role in adult heart disease. McCully's hypothesis didn't get much attention, though, until the 1990s, when several large-scale studies began implicating homocysteine as the possible cause of heart problems.

In a Harvard study of 15,000 physicians reported in 1992 in the Journal of the American Medical Association, 5 percent of the group with the highest homocysteine levels had at least three times the risk of heart attack than people with lower levels. Three years later, researchers from the University of Washington in Seattle reported in the same journal that perhaps 10 percent of the risk of cardiovascular disease may be attributed to elevated homocysteine levels. The researchers based their estimate on an analysis of 38 studies looking at homocysteine's connection to heart disease.

Diet vs. Vitamin Supplements

Vitamin supplements can lower blood homocysteine levels, often very dramatically. However, studies in people taking supplements have not consistently demonstrated less heart attacks and strokes even when the blood homocysteine levels fall. Until there is more evidence, a reasonable approach to a mildly elevated homocysteine level is to increase dietary intake of healthy foods rich in folic acid, B6 and B12. Also taking one multiple vitamin per day is safe and inexpensive.

For very elevated blood homocysteine levels, supplemental vitamins can be considered.