High blood pressure (hypertension) is a condition in which a person’s blood pressure is elevated. Blood pressure is the measure of the force of the blood pushing against the walls of the arteries – the blood vessels that carry blood from the heart to the rest of the body. If the high blood pressure has no known cause (more than 90 percent of cases), it is known as primary, essential or idiopathic hypertension. If it is caused by another condition, such as kidney disease, it is known as secondary hypertension. However, because of the complex variety of systems that influences blood pressure, these distinctions have blurred somewhat in clinical practice.

Blood pressure measurement is inexpensive and easily performed. Blood pressure is measured in two phases that correspond to the natural contractions of the heart. When the heart contracts (e.g., systole), the pressure of blood against arterial walls is known as systolic pressure. When it relaxes (diastole), the pressure of blood against arterial walls is known as diastolic pressure.

Blood pressure is always expressed as systolic pressure over diastolic pressure. Normal blood pressure for adults is considered to be below 120/80 millimeters of mercury (mm/Hg). Generally, blood pressure above 140/90 is considered to be high for adults, and blood pressure under 90/60 is considered to be low for adults (hypotension). High blood pressure may be diagnosed if an individual has any of the following three conditions:

• Has a blood pressure reading of 140/90
• Is taking antihypertensive medication
• Has been found twice by a physician to have high blood pressure

A new category, prehypertension, is being used to refer to individuals with blood pressures between 120-139/80-89. Such individuals are typically not prescribed medication, but they are advised to adopt lifestyle modifications to help keep blood pressure from rising. Lifestyle modifications might include weight loss, diet, exercise, reducing salt intake and quitting smoking.

Although the cause of most cases of high blood pressure is unknown, researchers have uncovered evidence that blood pressure is associated with insulin resistance and/or elevated insulin levels (hyperinsulinemia). Both high blood pressure and insulin resistance are features of the metabolic syndrome, a cluster of abnormalities that includes obesity, elevated triglycerides and low HDL "good" cholesterol. A number of possible mechanisms have been proposed that would explain how insulin resistance contributes to hypertension. However, this link is still poorly understood.

Researchers have also identified dozens of genes that contribute to high blood pressure. Though this implies that some people inherit a propensity for high blood pressure, the association is more complicated. Researchers believe that about 30 percent of essential hypertension can be traced back to genetic abnormalities that run in families. Most recent studies seem to indicate that inherited high blood pressure is the result of multiple gene expressions. There is currently no genetic test that consistently identifies people at risk for developing high blood pressure.

Whatever its cause, high blood pressure exacts a tremendous cost from society. High blood pressure is a major risk factor for heart attack, stroke and heart failure. According to the American Heart Association, about 69 percent of people who have a first heart attack, 77 percent who have a first stroke and 74 percent who have congestive heart failure have blood pressure higher than 140/90 mm Hg. High blood pressure has also been linked to sleep apnea, which itself is associated with heart disease. Some recent research suggests that premature birth in males may result in an increased risk of high blood pressure later in life.

Overall, an estimated 28 percent of American adults have high blood pressure. Of those, 30 percent do not know they have the dangerous condition, which is why it has been sometimes called the “silent killer.” Prehypertension is present in about 28 percent of American adults, or about 59 million people. Among the people who have been diagnosed, adequate blood pressure control is a significant problem. According to estimates from the National Institutes of Health, as many as 70 percent of people who are diagnosed with high blood pressure do not have it adequately controlled.

Before age 55, men are more likely to suffer from high blood pressure than women. After age 50, however, women experience a gradual rise in blood pressure, possibly due to the loss of hormones associated with menopause. By age 74, women are much more likely to have high blood pressure than men. It is two to three times more common in women taking birth control pills than those not taking them, especially in women who are overweight or obese.

The condition is especially deadly among black Americans, who tend to be diagnosed at younger ages and with higher blood pressures than other ethnic groups. Within the black community, high blood pressure is more likely to be diagnosed among people who are middle-aged or older, less educated, overweight or obese, physically inactive, and have diabetes. Black women, in particular, seem to suffer from high rates of elevated blood pressure. They have an 85 percent higher rate of medical care visits for high blood pressure than white women.

Despite its wide-ranging reach and potentially serious consequences, high blood pressure is relatively easy to diagnose and can be controlled, either with medications or lifestyle modifications. It is very important that people with high blood pressure seek treatment and follow their physician’s plan. Left untreated, high blood pressure will gradually continue to rise, causing the heart to overwork itself to the point at which serious damage can occur. Untreated high blood pressure also places other systems (e.g., circulation) and organs (e.g., the kidneys) at greater risk of damage that could lead to dysfunction or failure.

Hypertensive patients are at increased risk of:

• Heart disease (e.g., heart failure, sudden cardiac death, cardiomyopathy) and arrhythmias.
  
  
• Stroke
  
  
• Accelerated coronary artery disease
  
  
• Aortic aneurysm (a weakness in the aortic wall where it balloons out to more than 1.5 times its normal size and is in danger of rupturing), often resulting in sudden cardiac death
  
  
• Kidney failure
  
  
• Retinopathy (eye disease that leads to loss of vision)

The risk of developing one or more of these serious health conditions increases as blood pressure rises. To help physicians and patients better understand the dangers associated with high blood pressure, blood pressure measurements have been ranked into categories based on increasing severity. The following categories apply to adults (age 18 and over) who are not taking medicine for high blood pressure and do not have a serious short-term illness:

* Optimal levels are with respect to heart disease risk. Unusually low readings (below 90/60) can also negatively affect heart health and should be reported to a physician.

**Prehypertension refers to individuals who do not have high blood pressure and who do not take blood pressure medication (antihypertensives) but who are considered to be at risk for developing high blood pressure and its associated risk for coronary artery disease and stroke. Earlier, such individuals may have been termed “high normal.” Prehypertensive individuals are typically not given medication, but are recommended to adopt lifestyle modifications where necessary to help keep blood pressure from rising. These include weight loss, diet, exercise, reducing salt intake, limiting alcohol intake and stopping smoking.

Although 120/80 is considered ideal, researchers at the National Heart, Lung and Blood Institute (NHLBI) report that the risk of developing coronary artery disease can begin at blood pressures little higher than 115/75 mmHg, and that risk doubles with each 20/10 mmHg increment.

An important exception to the information listed above is noted among patients with diabetes and/or kidney disease. In these patients, hypertension is associated with an exceptionally higher rate of complications. These patients will require treatment if their blood pressure is above 130/85. Research has found success with a new drug, indapamide. For individuals with diabetes and high blood pressure, the drug was seen to lower blood pressure without affecting blood sugar levels.