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What Is High Blood Pressure?

Blood pressure refers to the force of blood pushing against artery walls as it courses through the body. Like air in a tire or water in a hose, blood fills arteries to a certain capacity. Just as too much air pressure can damage a tire or too much water trying to push through a small garden hose can damage the hose, too much blood pressure can threaten healthy arteries and lead to life-threatening conditions such as heart disease and stroke.



High blood pressure, or hypertension, is the most common of all cardiovascular diseases in the industrialized world. It is the leading cause of stroke and a major cause of heart attack. In the U.S. alone, approximately 80 million people over age 6 have high blood pressure. That's one in four Americans and one in three adults. And one-third of people with high blood pressure are unaware that they have it.

A blood pressure reading appears as two numbers. The first and higher of the two is a measure of systolic pressure, or the pressure in the arteries when the heart beats and fills them with blood. The second number measures diastolic pressure, or the pressure in the arteries when the heart rests between beats.

Normal blood pressure rises steadily from about 90/60 at birth to about 120/80 in a healthy adult. If someone were to take your blood pressure immediately after you'd delivered a speech or jogged five miles, the reading would undoubtedly seem high. This is not necessarily cause for alarm: It's natural for blood pressure to rise and fall with changes in activity or emotional state.

It's also normal for blood pressure to vary from person to person, even from one area of your body to another. But when blood pressure remains consistently high, corrective steps should be taken.

People with blood pressure of 140/90 or higher on at least two occasions are said to have high blood pressure. If the levels remain high, the doctor will probably begin treatment. Patients with blood pressure readings of 200/120 or higher need treatment immediately. People with diabetes are treated if their blood pressure rises above 135/80, as this population already has a high risk of heart disease.

Researchers identified people with blood pressures slightly higher than 120/80 as a category at high risk for developing hypertension. This condition is called prehypertension and affects an estimated 50 million men and women in the U.S. It is now known to increase the likelihood of damage to arteries and the heart, brain and kidneys so that many more doctors are recommending early treatment.

Consistently high blood pressure forces the heart to work far beyond its capacity. Besides injuring blood vessels, it can damage the brain, eyes, and kidneys. Even so, many people with high blood pressure do not realize they have the condition. Indeed, hypertension is often called "the silent killer" because it rarely causes symptoms even as it inflicts serious damage on the body. Left untreated, high blood pressure can lead to vision problems, as well as to heart attack, stroke and other potentially fatal conditions, including kidney failure.

Hypertension may also lead to heart failure, a common but disabling condition that can cause breathing problems. Patients who have very high blood pressure are said to have malignant hypertension. The diastolic pressure in such cases usually exceeds 130 or a systolic pressure above 200. Malignant hypertension is a dangerous condition that may develop rapidly, causes organ damage very quickly and requires immediate medical attention.

Fortunately, high blood pressure can be controlled effectively. The first step is discovery, so have your blood pressure checked regularly.

High blood pressure is more likely in people who:

• Have a family history of high blood pressure, heart disease, or diabetes.
• Are black.
• Are pregnant or take birth-control pills.
• Are over age 50 (men: after ago 50; women: after menopause).
• Are overweight.
• Are not active.
• Drink excessively.
• Smoke.
• Eat foods high in fat or sodium.

What Causes It?

In as many as 95% of reported high blood pressure cases in the U.S., the underlying cause cannot be determined. This type of high blood pressure is called essential hypertension.

When a direct cause can be identified, the condition is described as secondary hypertension. Among the known causes of secondary hypertension, kidney disease ranks highest. The condition can also be triggered by tumors or other abnormalities that cause the adrenal glands (small glands that sit atop the kidneys) to secrete excess amounts of the hormones that elevate blood pressure. Birth-control pills (specifically those containing estrogen) and pregnancy can boost blood pressure, as can medications that constrict blood vessels.

Though essential hypertension remains somewhat mysterious, it has been linked to certain risk factors. High blood pressure tends to run in families, for example, and it is more likely to affect men than women. Age and race also play a role. In the U.S., blacks are twice as likely as whites to have high blood pressure, although the gap begins to narrow around age 44. After age 65, black women have the highest incidence of high blood pressure.

Essential hypertension is also greatly influenced by diet and lifestyle. The link between salt and high blood pressure is especially compelling. People living on the northern islands of Japan eat more salt per capita than anyone else in the world and exhibit the highest incidence of essential hypertension. By contrast, people who add no salt to their food show virtually no traces of essential hypertension. The majority of all people with high blood pressure are "salt sensitive," meaning that anything more than the minimal bodily need for salt is too much for them and leads to an increase in blood pressure. Other factors that have been associated with essential hypertension include obesity; diabetes; stress; insufficient intake of potassium, calcium and magnesium; lack of physical activity; and chronic alcohol consumption.

Medically reviewed by Michael Aronson, MD, July 2005.

Sources: "Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressue," (JNC VII), JAMA Express, May 15, 2003. "Hypertension: Journal of the American Heart Association," Summer 2003. Elliot W., "Clinical Features and Management of Selected Hypertensive Emergencies," Journal of Clinical Malignant Phase Hypertension," The West Birmingham Malignant Hypertension Register. Journal of Human Hypertension 2005 Jan; 19(1):69-75. The American Heart Association.

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