Peruse the aisles of any supermarket, and the message that cholesterol causes heart disease rings loud and clear. But soon attention will likely shift to another culprit: homocysteine. This amino acid is usually scant in the blood. But when slightly elevated, it may set the stage for the atherosclerosis that is so tightly linked to cholesterol. Controlling homocysteine level is a simple matter of taking more vitamins--folic acid in particular.