Americans have been hearing for a long time about the dangers of high blood pressure, but new guidelines from a federal heath agency sound a clear warning: If you think you are safe, chances are you are not.
The report by the National Heart, Lung, and Blood Institute says that almost a quarter of U.S. adults - an estimated 45 million people - fall into a "prehypertensive" category and should adopt healthier dietary and exercise habits. These are people who were in the normal, healthy range of blood pressure.
With a quarter of adults suffering from outright hypertension, that leaves only half of the adult population with healthy blood pressure. But recent data, the report points out, suggest that 90 percent of people who have normal blood pressure at age 50 will become hypertensive as they age - putting them at heightened risk for heart attacks, stroke, kidney failure and aneurysms.
"We can't predict who they are going to be," said Dr. Stephen W. Havas, an epidemiologist with the University of Maryland School of Medicine who served on the committee that wrote the guidelines. "We have to presume that we are all at risk of becoming hypertensive."
That, he said, should prompt Americans to take a more serious approach to diet and exercise, and persuade doctors to become more engaged in monitoring a patient's blood pressure.
The guidelines, which were released Wednesday a week ahead of their publication by the Journal of the American Medical Association, created a new category called prehypertension.
People in this category have a systolic blood pressure ranging from 120 to 139 millimeters of mercury, and a diastolic pressure of 80 to 89. (Systolic is the top number, and diastolic the bottom number, in a blood pressure reading.)
The committee, which represented 46 professional, voluntary and federal organizations, did not suggest blood pressure medication for such people, recommending instead lifestyle changes including losing weight, exercising more, drinking less, and cutting fat and salt consumption. For overall cardiovascular health, people should also quit smoking.
People in the prehypertensive category are now thought to be at increased risk for developing hypertension. "Depending on what age range you're in, we estimate that you have a 20 to 50 percent likelihood of developing hypertension in just four years," said Havas.
But the condition has more immediate health implications, he said. Recent data from the Framingham Heart Study suggest that the risk of heart disease, stroke, kidney failure and heart failure doubles for every 20-point increase over 115 in a person's systolic pressure. The Framingham study is a long-term look at the factors that contribute to heart disease.
That means, for instance, a doubling of risk for a person whose systolic pressure rises from 115 to 135.
"In the past, you might say this is normal blood pressure and not much else needs to be done," said Dr. Roger Blumenthal, director of preventive cardiology at the Johns Hopkins School of Medicine and a spokesman for the American Heart Association. "Now, the guidelines are trying to push the idea that it's prehypertension. If you are not successful in improving lifestyle, it is likely you will develop one of the manifestations of heart disease."
The new guidelines come from understandings reached during the past half-decade about the course of high blood pressure.
"We now know that damage to arteries begins at fairly low blood pressure levels - those formerly considered normal and optimal," said Dr. Claude Lenfant, director of the National Heart, Lung, and Blood Institute. "The harm begins long before people get treatment."
Hypertension is a condition in which the blood vessels become abnormally stiff, forcing the heart to work harder to force blood through the body. It is a cascading cycle: Increased pressure within the vessels causes more stiffness, and the heart must work ever harder.
High blood pressure was listed as a primary or contributing cause of about 227,000 deaths in 1999, according to the American Heart Association.
The guidelines also call on food manufacturers and restaurants to cut in half their use of salt during the next decade. "Salt is one of the driving forces of the epidemic of hypertension in this country," said Havas, the prime author of the salt-lowering goal. The same statement was endorsed this year by the American Public Health Association.
Recent studies by the Center for Science in the Public Interest found 4,000 milligrams or more of salt in many restaurant entrees, well above the recommended daily dose of 2,400 milligrams. The group found high sodium levels in unlikely places, including tuna sandwiches, some of which had more than 1,000 milligrams.
"The bottom line is that Americans must change how they think about blood pressure," said Dr. Edward J. Rocella, coordinator of the NHLBI's high blood pressure education program. "The sooner they take action, the better. "
The heart agency offers educational information on a Web site: www.nhlbi.nih.gov/hbp.