Cardiovascular disease (CVD) and cancer are common problems for Americans. Shortages of antioxidant vitamins (vitamins A, C, and E; beta-carotene; and folic acid) are associated with the blood vessel changes that occur in CVD. Therefore, people have thought that taking these vitamins might reduce the chances of developing CVD. Similarly, information suggests that these vitamins might lower a person's chances of developing cancer. Many studies have examined associations between particular vitamins and CVD and cancer. The studies vary in quality, and their results often conflict.