FRIDAY, June 23 (HealthDay News) -- Until recently, doctors treating high blood pressure limited their concern to blood pressure that exceeded a reading of 140 systolic (the upper number) and 90 diastolic (the lower number).

About two-thirds of Americans over age 65 have this level of high blood pressure, according to federal health statistics.

But now medical experts say the damage done by elevated blood pressure starts at levels much lower than that, when people are experiencing a less severe condition known as "prehypertension." That's the term given to blood pressure ranging from 120/80 to 139/89, higher than normal but not within the traditional danger zone.

"There's always been this ambiguity about this blood pressure that's not normal, but not high blood pressure either," said Dr. Adnan I. Qureshi, director of the cerebrovascular program in the Zeenat Qureshi Stroke Research Center at the University of Medicine and Dentistry of New Jersey. "But we now know that when you have prehypertension, you have a three-times greater risk of having a heart attack than people with normal blood pressure."

Blood pressure is the force exerted by blood against the walls of arteries. High blood pressure is dangerous because it makes the heart exert itself too hard and contributes to atherosclerosis, or hardening of the arteries, according to the National Institutes of Health.

High blood pressure, also known as hypertension, increases the risk of heart disease and stroke, which are the first- and third-leading causes of death among Americans. It also can result in other conditions, such as congestive heart failure, kidney disease and blindness.

Nearly one of every three American adults, some 65 million people, has high blood pressure. People tend to develop high blood pressure as they get older, with middle-aged Americans facing a 90 percent chance of having it during their lives.

African-Americans are at greater risk of developing high blood pressure and have been shown to get it earlier in life and more often than whites. Others at risk for developing high blood pressure are people who are overweight, those with a family history of hypertension and those with prehypertension.

Recent studies have shown that people with prehypertension are three times more likely to have a heart attack and 1.7 times more likely to develop heart disease. An estimated 59 million Americans have prehypertension.

It's important to detect and treat high blood pressure early, to limit the condition's effects on the body, said Dr. Jeffrey Cutler, a senior advisor for the National Heart, Lung, and Blood Institute.

"Over the years, the higher pressure damages and aggravates diseases of the arteries," Cutler said.

Luckily, blood pressure is a condition that receives regular medical attention. "When you go see a doctor for anything, you get your blood pressure checked," Cutler said.

He recommended that people not rely on automatic blood-pressure machines, like those found in drug stores or supermarkets. "Those cuffs are not well-maintained or very accurate, and we discourage dependence on them for reassurance that your blood pressure's OK," Cutler said.

Once you've got high blood pressure, or prehypertension, a range of treatments are available.

Lifestyle changes are the first line of defense -- keeping your weight down, exercising regularly, reducing salt in your diet, cutting down on drinking, quitting smoking, and following a healthy eating plan that emphasizes fruits, vegetables and low-fat dairy foods.

But that only goes so far, Cutler said.

"Studies have shown that the majority of patients will need some medication," he said. "Some well-motivated people can get there with lifestyle changes, but not many."

The problem with prehypertension is that it falls within a gray area where medicine will not necessarily help, Qureshi said.

"With hypertension, we know that medication may be beneficial. With prehypertension, we don't know that yet," he said.

"It's still an evolving body of knowledge," Qureshi added. "We know prehypertension needs to be addressed, but we don't know what to do with these patients, and there are so many of them that we can't ignore the problem. Whatever we come up with will have true public impact."

For now, doctors are recommending that prehypertensive patients follow the same lifestyle changes as people will full-blown high blood pressure, Qureshi said.

"The real message for the public is that if you are prehypertensive, do not ignore it," he said. "You do have something to worry about."

More information

To learn more about prehypertension, visit the National Heart, Lung, and Blood Institute.

SOURCES: Jeffrey Cutler, M.D., senior advisor for the National Heart, Lung and Blood Institute, Bethesda, Md.; Adnan I. Qureshi, professor and director of the cerebrovascular program in the Zeenat Qureshi Stroke Research Center at the University of Medicine and Dentistry of New Jersey, Newark

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