Encyclopedia / H / Hypertension (High Blood Pressure)

Hypertension (High Blood Pressure)

What Is Hypertension?

Hypertension (high blood pressure) is characterized by a persistent increase in the force that the blood exerts upon the walls of the arteries. It is normal for this force to increase with stress or physical exertion, but with hypertension, blood pressure is high even at rest.

Because blood pressure in the arteries rises and falls with each heartbeat, it is measured with two numbers: systolic (the top number in a reading) and diastolic (the bottom number). The systolic number reflects the force of blood against the arterial walls each time the heart contracts. Diastolic pressure refers to the pressure within the arteries as the heart relaxes and refills with blood (which explains why the diastolic number is always lower than the systolic measurement).

Blood pressure is measured in millimeters of mercury (abbreviated mm Hg) using a device called a sphygmomanometer. A traditional sphygmomanometer uses a column of mercury to measure blood pressure; newer blood pressure monitors are digital. Hypertension is defined as systolic pressure greater than 140 mm Hg or diastolic pressure greater than 90 mm Hg. Optimal blood pressure is less than 120/80 mm Hg.

Approximately 60 million people in the United States have hypertension, but only about half of them know it—primarily because it so rarely causes any noticeable symptoms and is usually detected only incidentally during a routine physical examination. If left untreated, hypertension promotes atherosclerosis (narrowing of the arteries) and increases the risk of heart attack, stroke, kidney damage, and destruction of tiny blood vessels in the eye, which can result in vision loss. For these reasons hypertension is often called “the silent killer.” Fortunately, if detected early and treated properly, the prognosis is good.

The National Heart, Lung, and Blood Institute classifies blood pressure as normal, prehypertension, hypertension stage 1, and hypertension stage 2.

Categories for Blood Pressure Levels in Adults (measured in millimeters of mercury, or mmHg)



(top number)


(bottom number)


Less than 120


Less than 80





High blood pressure

Stage 1




Stage 2

160 or higher


100 or higher

In 2013, new blood pressure guidelines formulated by an expert panel were released in a report in the Journal of the American Medical Association. These guidelines do not include different stages of hypertension. Instead, they recommend that adults age 60 and older should aim for blood pressure under 150/90 mm Hg. For younger adults, the target blood pressure should be under 140/90 mm Hg. Your doctor will take into account not only your age, but also your medical history in determining what your blood pressure goals should be.

Who Gets Hypertension?

As many as 9 out of 10 people are diagnosed with some degree of hypertension after the age of 50, but high blood pressure also is becoming increasingly common among children and adolescents. It is probably the most common medical problem in the industrialized world, and is the major treatable risk factor for heart attack and stroke. Untreated hypertension affects all the body’s systems and can shorten life expectancy.


Most people with hypertension experience no symptoms. However, when blood pressure is dangerously high, it may produce symptoms in some people that include headaches, dizziness, ringing in the ears, nosebleeds, and palpitations.

Causes/Risk Factors

  • In more than 90 percent of hypertension cases, no single identifiable cause can be pinpointed—but lifestyle factors play a critical contributing role. This form of hypertension is called essential hypertension. Risk factors for essential hypertension include the following:

  • Emotional stress.

  • Family history of hypertension.

  • Gender (risk is one-half to two-thirds higher in men).

  • Race (compared to white Americans, African-Americans have up to twice the incidence of hypertension).

  • Sedentary lifestyle.

  • Obesity, excessive alcohol consumption, cigarette smoking, and a high-sodium diet also increase the risk of essential hypertension.

  • When an underlying cause can be identified, the condition is known as secondary hypertension. Such causes include kidney disorders, adrenal tumors, and pregnancy.

What If You Do Nothing?

Blood pressure often increases with age—so if you are in your 30s and your blood pressure is slightly elevated, it may eventually rise into the hypertension category. In addition, if you have certain lifestyle risk factors for hypertension—you smoke, are overweight, consume too much alcohol, or are sedentary—and you do nothing to modify these factors, your blood pressure is likely to increase over time. For example, if your blood pressure is normal and you are sedentary, you have a 20% to 50% greater risk of developing hypertension than a person who’s fit and active.


  • Diagnosis of hypertension requires accurate measurements of elevated blood pressure on at least three different occasions over a period of a week or longer.
  • Some people exhibit “white coat hypertension,” wherein blood pressure is consistently high in a clinical setting (i.e., at the doctor’s office) but is normal when measured at home. In others, blood pressure alternates sporadically between normal and high readings (known as labile hypertension). Patients may be asked to wear a portable monitor that automatically records blood pressure periodically over the course of a day or so to get accurate readings.
  • Blood and urine tests to detect kidney damage and electrocardiogram (ECG) to check for heart damage (both possible complications of hypertension) may be performed.


  • The first line of treatment for essential hypertension involves adopting healthy lifestyle measures. Mild hypertension may respond positively to lifestyle measures and thus require no further medical therapy. For example, some studies indicate that as many as 30 percent of those with high blood pressure (specifically, the type known as sodium-sensitive hypertension) can control it by lowering their salt intake.
  • If lifestyle changes prove inadequate, your doctor will prescribe one or more of the many available drugs. These include:
  • Diuretics (or “water pills”) increase elimination of salt and water and thus reduce overall body-fluid volume. (Some diuretics deplete the body’s levels of potassium, thus requiring potassium supplementation.) One of the most commonly used diuretic agents is hydrochlorothiazide (HydroDiuril, Microzide).
  • Beta-blockers (atenolol, bisoprolol, carvedilol) interfere with nerve receptors in the heart, causing it to beat less forcefully. In addition to lowering blood pressure, beta-blockers have been shown to benefit patients with heart disease.
  • Calcium channel blockers (amlodipine felodipine, idradipine) reduce the ability of arterial walls to constrict. Calcium channel blockers may have serious side effects and should be used with caution in patients with pulmonary arterial hypertension, which is a life-threatening condition.
  • ACE inhibitors (captopril, enalapril, lisinopril) prevent the formation of a hormone that constricts blood vessels. ACE inhibitors are usually tolerated well, but there are potential side effects—most commonly a chronic nonproductive cough that affects about 10 percent of patients.
  • Alpha-blockers (tamsulosin, doxazosin) and central alpha agonists (clonidine, methyldopa) interfere with nerve impulses that cause arteries to constrict.
  • Vasodilators (hydralazine, minoxidil) relax and dilate the arterial walls. To prevent fluid retention and a rapid heartbeat, they must be used in combination with a diuretic and a beta blocker. Vasodilators also cause headaches and joint pain.
  • For secondary hypertension, the underlying disease must be identified and treated.


  • Keep your weight within a healthy, normal range.
  • Eat a diet rich in fruits, vegetables, and whole grains, and low in saturated fat and cholesterol.
  • Avoid smoking and restrict alcohol intake to no more than two drinks a day.
  • Aim to get at least 20 minutes of vigorous aerobic exercise (like jogging, biking, dancing, or swimming) a day, three or four days a week.
  • Limit sodium intake. Guidelines from the U.S. Department of Agriculture recommend less than 2,300 mg of sodium a day—and less than 1,500 mg if you’re 51 or older. The American Heart Association now recommends that everyone keep daily intake to less than 1,500 mg per day.

When to Call Your Doctor

  • All adults should have their blood pressure checked at least once a year. This practice is especially important if you are male, over age 40, overweight (particularly if you have been overweight since youth), sedentary, or if you have a family history of hypertension or heart disease.
  • Notify your doctor if you experience any unpleasant side effects from antihypertensive medications. Adjustments in your prescription may eliminate the problem; never stop taking your medication without consulting your doctor.
  • Get prompt medical attention if you experience symptoms such as ringing in the ears, dizziness, or recurrent headaches or nosebleeds—these may be signs of dangerously high blood pressure.

Reviewed by Michael S. Soliman, M.D., family medicine physician in private practice and hospitalist at Mount Holyoke Medical Center, Mount Holyoke, MA.