Sometimes even seemingly rock-solid medical truths are surprisingly fluid. High cholesterol is bad for the heart, right? Well, yes. But up to 50 percent of heart attack victims have cholesterol levels that fall squarely in the ``normal'' range.

What is behind these attacks?

While the jury is still out, some researchers blame a little-known amino acid called homocysteine that is a byproduct of normal metabolism.

Dr. Kenneth Cooper, founder of the Cooper Aerobics Center in San Antonio, has called homocysteine ``the cholesterol of the 21st century.''

The amino acid is a hot topic in medical research. No fewer than 400 scientists from 32 countries attended the recent Third International Conference on Homocysteine Metabolism held in Italy.

The potential danger posed by homocysteine has already been suggested in a number of studies. For example, an analysis in the Journal of the American Medical Association concluded that a high level of homocysteine was an independent risk factor for vascular disease. And a four-year Norwegian study published in the New England Journal of Medicine found that patients with the highest levels were four times more likely to die of heart disease than those with the lowest.

Homocysteine also has been linked to a variety of ailments, from miscarriages and birth defects to Alzheimer's disease, rheumatoid arthritis, osteoporosis and vision problems.

At high-enough levels, homocysteine is believed to scar the interior of artery walls, which can help trigger a buildup of heart attack- and stroke-causing blood clots. In rare cases, high homocysteine is caused by a genetic problem, a condition called homocystinuria. In most people, however, it is caused by a deficiency in vitamins B-6, B-12 and folate (folic acid), also a B-vitamin. In the body, these nutrients render homocysteine into harmless byproducts.

So far, the studies have found only an association between homocysteine and heart disease. In other words, there has been no concrete proof that homocysteine is causing the damage.

For example, one study of 15,000 initially healthy adults published in the journal Circulation found that a high level of homocysteine was not significantly associated with development of heart disease. Indeed, the strongest association was with vitamin B-6. Those with the highest levels of this vitamin had only one-third the heart disease rate of those with the lowest levels.

What makes this study interesting, said the lead author, Dr. Aaron R. Folsom, is that it started with healthy individuals.

``Most previous homocysteine studies have looked at people who already had heart disease,'' said Folsom, who is with the School of Public Health at the University of Minnesota in Minneapolis.

Follow-up studies are needed to determine whether high homocysteine causes, or is simply a symptom of, heart disease.

For most people, eating more unprocessed foods rich in B-vitamins (such as fruits, vegetables, enriched grain products, and meat and dairy products) can lower homocysteine levels. To be on the safe side, most experts recommend taking a multivitamin.

Although Americans consume an average of about 350 micrograms of folic acid a day, studies have shown than anything less than about 400 micrograms increases risk of vascular disease.

Dr. Marianne Lagato, founder of the Partnership for Women's Health at Columbia University in New York, gives her heart patients 1,000 micrograms - one milligram - a day to lower homocysteine.

``It's perfectly safe,'' she said.

Blood tests for homocysteine have been available for several years and a doctor can order one as part of a regular checkup. Because of the cost (about $50 per test) and a lack of conclusive evidence showing benefits of reducing homocysteine levels, however, the American Heart Association does not recommend testing for the general public. Some experts disagree, but the association suggests only that those with a personal or family history of heart disease should consider being tested.

Homocysteine levels are measured in micromoles per liter of blood. There is some evidence that levels below 8 or 9 significantly reduce risk. Among the general population, the mean homocysteine level is between 11 and 12. Some studies also suggest that risk is proportional, even within the normal levels. In other words, even small changes can have big benefits, and the lower the homocysteine level the better.

　　From Express-news.net