Hypertension is diagnosed when blood pressure readings are 140/90 mm Hg (millimeters of mercury, the height of mercury in the gauge) or higher on at least two doctor visits. At least 65 million Americans have hypertension, and nine out of 10 middle-aged people will eventually develop the condition. Although hypertension may not produce symptoms, it is a serious condition and is a primary cause of stroke, coronary heart disease, heart failure, kidney disease, and blindness. In most cases, hypertension is easily detected and usually controllable with lifestyle modifications—such as diet and exercise—and medication.
Blood pressure readings include two values: Systolic pressure, the higher number, corresponds with the peak pressure in the arteries when the heart contracts; diastolic pressure, the lower number, reflects the lowest pressure in the arteries as the heart relaxes. People with a blood pressure level less than 120/80 mm Hg have normal blood pressure. People with a systolic blood pressure between 120 and 139 mm Hg or a diastolic blood pressure between 80 and 89 mm Hg have a condition called prehypertension. These individuals are at increased risk for developing hypertension. Losing weight, eating a diet rich in fruits and vegetables, reducing salt intake, increasing physical activity, moderating alcohol consumption, and quitting smoking can help lower the risk. Most individuals with hypertension should aim to keep their blood pressure below 140/90 mm Hg. For those with diabetes or kidney disease, blood pressure should be maintained below 130/80 mm Hg.
Blood pressure, the amount of tension that blood exerts on the walls of blood vessels as it travels through the circulatory system, rises and falls with each heartbeat. Systolic pressure, the higher number, corresponds with the peak pressure in the arteries when the heart contracts; diastolic pressure, the lower number, reflects the lowest pressure in the arteries as the heart relaxes.
Blood pressure fluctuates throughout the day under the direct influence of the heart, the arteries, and the kidneys. During exercise, for example, the heart beats faster and more forcefully to raise blood pressure and deliver extra oxygen and nutrients to the muscles; blood pressure drops as the heart slows during sleep. Dilation of small arteries decreases blood pressure, while constriction of these arteries increases blood pressure. The kidneys affect blood pressure by increasing or decreasing the amount of sodium and water excreted in the urine, which affects the volume of blood in the arteries. The heart, arteries, and kidneys control blood pressure through an elaborate network of nerves and hormones.
Normally, this complex regulatory system allows blood pressure to rise and fall as needed while staying within a desirable range. In many people, however, abnormalities in this system lead to chronically elevated blood pressure, or hypertension.
Causes of Hypertension
In 90 percent to 95 percent of people, it is difficult to pinpoint the exact cause of hypertension. In these individuals, the condition is called primary hypertension. When hypertension has an identifiable cause, it is called secondary hypertension. About 5 percent of people with hypertension fall into this category.
Some people have white coat hypertension—high blood pressure readings that are present only when they are examined by a physician. Whether to treat white coat hypertension with antihypertensive medication is a controversial question. Many specialists believe that people with white coat hypertension who do not have other risk factors for cardiovascular disease (such as high cholesterol levels or diabetes) do not need to take medication. Instead, they should adopt lifestyle measures such as eating a healthy diet and exercising regularly. However, the general consensus is that people with white coat hypertension who have organ damage from hypertension (for example, kidney or heart disease) need treatment with medication.