Nearly two-thirds of Americans have or are on the verge of developing high blood pressure (search), which not only raises their risk of heart disease and stroke but also increases their immediate risk of hospitalization and death, according to new research.

Despite these risks, researchers say only about a third of people with high blood pressure are aware of their condition or have it under control.

Three new studies published in the Oct. 25 issue of the Archives of Internal Medicine highlight the risks associated with prehypertension, (search) a new classification announced last year that includes people at risk for developing high blood pressure or hypertension.

Prehypertension is defined as having systolic blood pressure (search) (the top number in a blood pressure reading) of 120-139 points or a diastolic blood pressure (search) (the bottom number) of 80 to 89. A person's blood pressure is considered high if the systolic pressure is over 140 or the diastolic is over 90.

In two separate studies, researchers looked at how common this new blood pressure category is among U.S. adults. They also estimated how common other risk factors for heart disease are among those with prehypertension. A third study used a model to estimate the effect of prehypertension and uncontrolled high blood pressure on hospitalization and death rates in the U.S.

Prehypertension Risks Run High

The first two studies found about 30 percent of Americans had prehypertension and another 30 percent had high blood pressure. Men were more likely than women to have prehypertension, and the prevalence of prehypertension increased dramatically with age.

For example, one study showed the prevalence of prehypertension increased from 40 percent among people aged 18 to 39 to 88 percent among those over 60.

Of the persons studied with prehypertension:

—African Americans had the highest rates of prehypertension, and Mexican Americans had the lowest.

—Obesity was closely associated with high blood pressure. About 60 percent of overweight adults and 76 percent of obese adults had either prehypertension or high blood pressure.

—Higher education was associated with lower rates of prehypertension and high blood pressure (54 percent among those with more than a high school education vs. 65 percent among those with less than a high school education).

Researchers also found that only two-thirds of people with high blood pressure were aware of their condition, and less than two-thirds of those had adopted healthy lifestyle changes or taken drugs to control their blood pressure. As a result, only 31 percent had their blood pressure under control.

In a related study, researchers found people with prehypertension were 1.65 times more likely to have at least one other risk factor for heart disease and stroke than those with normal blood pressure.

Researchers estimate that together, prehypertension and untreated high blood pressure accounted for 5 percent of hospital admissions per 10,000 adults aged 25 to 74 years, 10 percent of nursing home admissions, and 14 percent of deaths.

Of these, the study suggests that prehypertension alone accounted for about 3 percent of hospitalizations, 7 percent of nursing home stays, and 9 percent of deaths.

"People need to adopt lifestyle modifications, change their diets, try to be more active and get more exercise, quit smoking," says researcher Youfa Wang, MD, PhD, of the University of Illinois at Chicago, in a news release. "This can all help control blood pressure, reduce the risk of developing hypertension and future risks of cardiovascular disease."

By  Jennifer Warner, reviewed by  Brunilda Nazario, MD

SOURCES: Wang, Y. Greenlund, K. Russell B. Archives of Internal Medicine, Oct. 25, 2004; vol 164: pp 2126-2134, 2113-2118, 2119-2124. News release, University of Chicago.