High blood pressure is sometimes referred to as hypertension. Approximately 30% of American adults have prehypertension or stage 1, 2, and 3 hypertension (see table 3.1, p. 45). Hypertension is a major risk factor for cardiovascular disease. Hypertension is often called the "silent killer" because it damages many organs without ever causing pain. The longer the condition exists, the greater the damage and the increased risk of cardiovascular disease. Regular physical activity, with a physician's approval, is an important part of any program used to lower high blood pressure. Check out Your Guide to Lowering High Blood Pressure.