Scientists from the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health in Bethesda, MD and Emory University Hospital in Atlanta have found that levels of a type of adult stem cell in the bloodstream may indicate a person's risk of developing cardiovascular disease. The study looked at the blood level of endothelial progenitor cells, which are made in the bone marrow and may help the body repair damage to blood vessels. They found that cardiovascular disease risk was higher in persons with fewer endothelial progenitor cells. The scientists believe that these endothelial progenitor cells patch damaged sites in blood vessel walls.