March 9, 2011, 5:40 pm
Rethinking ‘Normal’ Blood Pressure
By TARA PARKER-POPE
Millions of people who have been told they are on the path to hypertension may never develop life-threatening problems, according to new research that suggests it’s time to redefine “normal” blood pressure.
The findings, from researchers at the Veterans Affairs Health Care System in Minneapolis and the University of Minnesota, suggest that as many as 100 million Americans who have been told they have a condition called prehypertension may face no added mortality risk and therefore could reasonably be considered to have normal blood pressure.
The authors reviewed two decades of blood pressure data that tracked 13,792 people from the National Health and Nutrition Examination Survey, which enrolled participants from 1971 to 1976. The researchers also reviewed similar data for 6,682 adults from a similar survey carried out between 1959 and 1962.
Current guidelines label people with blood pressure above 120/80 millimeters of mercury as having prehypertension and at higher risk for serious health problems like heart attack and stroke than people with lower blood pressure. But the data review found that people in that category are not any more likely to die prematurely than those with lower blood pressures, according to the study, published in The Journal of General Internal Medicine.
“If we can’t identify an increased risk, is that where abnormal should be set?’’ said Brent Taylor, core investigator for the V.A. in Minneapolis and assistant professor of medicine at the University of Minnesota. “It should at least start a conversation about why normal is set where it is. If we make small changes to where we set normal blood pressure, it has huge implications in the numbers of people we identify as being at risk.’’
The current guidelines were determined in 2003, when the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure issued its seventh report updating recommendations. The report was the first time that the panel identified relatively low blood pressure readings as an indicator of future disease. As a result of the findings, tens of millions of people were told they were at risk and were urged to adopt lifestyle changes to prevent blood pressure from creeping higher.
In the latest study, researchers focused on relatively older data because blood pressure treatment was not as prevalent years ago, and as a result, they could better study the health effects of changes in blood pressure as people age. Among people over 50, the most meaningful predictor of poor health was the systolic blood pressure — the first, or upper, number given in a blood pressure reading. In this older group, a systolic pressure of 140 or higher was most predictive of mortality. Among people under 50, it was the diastolic pressure, or second number, that was most predictive. In this group, a diastolic pressure of 100 or more was most predictive of poor health. In younger people, having a systolic reading of 200 or higher was also predictive of higher mortality.
Dr. Taylor said it’s important that the guidelines home in on the people who can most benefit from treatment. He also noted that blood pressure guidelines can end up hurting people if they wrongly label someone as being at risk.
“Maybe those people should be focusing on conditions other than their borderline blood pressure,” Dr. Taylor said. “If we intervene with these people who don’t have a lot of risk, maybe we’re going to cause more harm than benefit.”
Dr. Aram V. Chobanian, president emeritus of Boston University, who was chairman of the 2003 guidelines panel, said those recommendations were based on studies showing that the risk of heart disease starts to rise at readings as low as 115/75.
Dr. Chobanian said he had not read the latest study, which looked at mortality risk rather than heart disease risk, but noted that other doctors have raised concerns about a designation of prehypertension for people with blood pressure of 120/80.
“Some physicians feel it’s an overemphasis, and I understand that,” he said. “If you identify individuals who are candidates for prevention of hypertension, that to me is the greatest point of it, to pick out people whom you want to make — or try to make them — change their lifestyle.”
Dr. Taylor noted that a single study is not likely to change the guidelines, but he hopes the research will be included in the discussion of blood pressure guidelines. The eighth Joint National Committee panel is currently reviewing the guidelines and is expected to make draft recommendations later this year.