Doctors of USC

Fully half of all heart attacks occur unexpectedly in people with none of the traditional risk factors for cardiovascular disease.

That has led scientists to search for novel risk factors that will better predict in whom heart disease, the nation's biggest killer, will strike next. Leading the line-up is homocysteine, an amino acid.

High levels of homocysteine can damage arteries and may encourage thrombosis, the blood clotting that can lead to a heart attack or stroke. "It's the next big risk factor that scientists need to sort out," says Howard N. Hodis, M.D., director of the USC Atherosclerosis Research Unit. Called by some scientists "the cholesterol of the next century," homocysteine has been linked to cardiovascular disease in many studies.

Nearly 50 percent of people who have heart attacks or strokes have high blood levels of homocysteine. Diets rich in protein may raise homocysteine levels. But a diet packed with folic acid, vitamin B6 and vitamin B12 brings levels down.

Right now, a large study at the National Institutes of Health is investigating whether vitamin supplementation can lower risk of stroke. The interplay between vitamins and homocysteine has led many researchers to wonder whether homocysteine itself is truly responsible for the increased risk.

Some speculate it may reflect a different problem-too little vitamin B6 and folate. Green, leafy vegetables, fruits and legumes contain high levels of these vitamins.

"So much is still unclear about homocysteine and heart disease that it is premature for patients to be tested for it or to take supplements in the hopes of reducing it," Hodis says. "But in the future there may be as many as 100 biochemical markers done on patient's blood panel to help gauge risk."

In the meantime, he suggests paying attention to today's well-known risk factors: high cholesterol, cigarette smoking, high blood pressure, diabetes, obesity, physical inactivity and a high-fat diet.