What Is Prehypertension? In prehypertension, the systolic (top number) reading is 120 mmHg-139 mmHg, or the diastolic (bottom number) reading is 80 mmHg-89 mmHg. Prehypertension is a warning sign that you may get high blood pressure in the future. High blood pressure increases your risk of heart attack, stroke, coronary heart disease, heart failure, and kidney failure. There's no cure for high blood pressure, but there is treatment with diet, lifestyle habits, and medications. We know that starting as low as 115/75 mmHg, the risk of heart attack and stroke doubles for every 20-point jump in systolic blood pressure or every 10-point rise in diastolic blood pressure for adults aged 40-70. Who Is at Risk for Prehypertension? Nearly half of all adults older than age 18 have prehypertension or hypertension, as measured by average of two or more readings at two or more doctor's visits. According to the American Heart Association, 59 million people in the U.S. have prehyperte...