To Your Health

Q. I keep hearing about a marker for heart disease called homocysteine. What is homocysteine, and why is it a problem?

A. Homocysteine is a toxic amino acid produced by the incomplete metabolism of L-methionine, one of the nutritionally essential amino acids. High blood homocysteine levels are now recognized as a strong "independent risk factor" in heart disease. Elevated homocysteine is one of several independent risk factors, different from the risk associated with high cholesterol, that you might want to check out through your physician.

Elevated homocysteine was once thought to result from a rare genetic defect that usually responds to exceptionally liberal vitamin B-6 supplements. However, about 30 years ago Dr. Kilmer McCully began to publish scientific papers revealing homocysteine as one of the strong indicators of heart disease. Although his research was ignored until the 1990s, the connection of homocysteine with heart disease and several other problems is now well established.

Homocysteine becomes elevated when too much is produced (usually related to vitamin B-6 deficiency) or when it is not recycled back to methionine (usually related to vitamin B-12 and folic acid deficiencies). Since elevation of homocysteine can result from either mechanism, both possibilities should be guarded against through supplementation with vitamin B-6, vitamin B-12, and folic acid.

In some people, supplements of these three vitamins at several times the recommended daily allowance (RDA) are required to normalize homocysteine. Readily available multivitamins with sufficient amounts of vitamins B-6 and B-12 can be purchased without government restriction, but a legal limitation imposed by the Food and Drug Administration sets an upper limit on folic acid. The allowable amount of folic acid is the current RDA, or 0.4 milligrams per day (unless the pill is labeled "For Pregnant and Lactating Women," in which case 0.8 mg is allowed). For comparison, B-complex vitamins like vitamins B-6 and B-12 can be purchased in amounts exceeding 100 times the RDA. Few Americans need a folic acid supplement 100 times the RDA, but it appears that a substantial number need amounts in the range of 3-5 times the RDA, though such amounts are illegal to sell in America as a single pill.

It appears that homocysteine is toxic in any amount, although your physician will likely not be alarmed unless your blood level exceeds 10-12 mmol/L. Double this amount of homocysteine will approximately double your risk of having a heart attack. A simple blood test would either set your mind at ease, if homocysteine level is normal, or give you a "heads up" if homocysteine levels are elevated.

Homocysteine does its damage by increasing the risk of blood clots, which are capable of reducing blood flow to vital organs such as heart and kidneys. Homocysteine may also increase the damage to LDL cholesterol, the form of cholesterol most susceptible to damage by oxygen and the form most likely to damage the walls of your blood vessels. Beyond heart disease and stroke, homocysteine elevation is associated with increased risk of some other illnesses such as rheumatoid arthritis.

In addition to nutritional deficiencies of vitamin B-6, vitamin B-12, and folic acid, coffee consumption is associated with increased homocysteine. In a research study, when people reduced coffee intake from four cups of coffee per day to none, both their blood homocysteine and cholesterol levels dropped. Strong black tea was also implicated in raising homocysteine.

Compared to the sometimes-austere dietary changes needed to reduce cholesterol, reducing your risk of heart disease by avoiding caffeine and adding a few pills to your daily routine seems rather attractive.