WASHINGTON, DC- Coronary artery disease now joins the list of diseases associated with increased levels of the amino acid homocysteine, according to a study conducted under the auspices of the U.S. Department of Agriculture.

The new data come from an analysis of 1,041 men and women ages 67 to 96 involved in the Framingham Heart Study. That study, now nearly 50 years old, is an ongoing analysis of cardiovascular risk factors in the community of Framingham, Mass. Researchers from several institutions including Tufts University and Boston University conducted ultrasound tests on the carotid arteries of the study participants to determine the degree of vessel narrowing. This is considered a good indication of the degree of arteriosclerosis, or artery thickening.

After obtaining the ultrasound measurements, the researchers then used statistical methods to determine the potential correlation between significant vessel narrowing (at least 25 percent of the inner diameter of the neck arteries) and blood levels of homocysteine and related vitamins.

The analysis revealed that participants with the highest homocysteine levels were twice as likely to have arteriosclerosis as those with the lowest levels of homocysteine. The odds decreased as plasma levels of folate and, to a lesser extent, vitamin B6 increased. In addition, the risk of significant narrowing increased at homocysteine levels previously considered to be normal. The current findings parallel earlier observations showing a relationship of high homocysteine to low B vitamin levels in the same study group.

Homocysteine is a sulfur-containing amino acid produced by demethylation of methionine, an amino acid essential for dietary metabolism. Conversion of this protein to methionine via methionine synthase is the only reaction in the human body that requires both folate and B12.

Without adequate amounts of both folate and vitamin B6, homocysteine cannot be converted into useful amino acids and thus builds up in the blood, explained lead author Jacob Selhub, a nutritional biochemist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston.

"This study strengthens the evidence that elevated homocysteine should be taken seriously as a risk factor for heart disease and stroke in older people. The prevalence of significant artery narrowing in our study population rose in line with their homocysteine levels even after accounting for other risk factors, including age, gender, cholesterol profile, systolic blood pressure and smoking status," notes Dr. Selhub.

The good news is that it's easy to correct elevated homocysteine through diet. Green vegetables and citrus are excellent sources of folate, said Selhub. And vitamin B6 is in a wide range of plant and animal foods. Whole grain products, bananas, fatty fish, nuts, poultry, red meat and organ meats are all rich sources. Both vitamins have been added to some breakfast cereals.

"It's not necessary to take vitamin supplements to get ample folate and vitamin B6. But it may be wise for older people who don't eat enough to add a supplement to their diet," he added.

The USDA study appears in the New England Journal of Medicine, 2/2/95.

Another group of researchers recently announced the discovery of a basic metabolic defect involving homocysteine and the development of spina bifida and other neural tube defects. A study of Irish mothers (see related story in Science Update) of children with neural tube defects revealed significantly higher blood levels of homocysteine during pregnancy than seen in mothers of normal children. The researchers believe a defect in the enzyme methionine synthase may produce the increase in homocysteine levels and the subsequent neural tube defects. Methionine synthase is a key enzyme in the production of the myelin sheath which surrounds the neural tube.

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