Normal Blood Pressure May Not Be Optimal – How Low Should It Go?

By reducing BP still more, patients were protected from heart attacks, cardiac arrest, angioplasty, hospitalization for chest pain, and death. Every 16 heart disease patients with normal blood pressure who received drugs to lower it, one adverse event was prevented over a two-year period. In addition, lower blood pressure appeared to slow or stop the growth of the fatty deposits called plaque in the coronary arteries, as compared with patients taking a placebo, whose plaque growth continued over the two-year study period.

The international study, by Dr. Steven Nissen of the Cleveland Clinic and his colleagues, is being published in The Journal of the American Medical Association. It found that for every 16 heart disease patients with normal blood pressure who received drugs to lower it, one adverse event was prevented over a two-year period.

While the study was fairly small, with 1,991 patients, blood pressure experts said its surprising result reopened a longstanding question: How low should blood pressure go?

These were heart patients who were at high risk for such events, Dr. Nissen said, but their blood pressure was considered so well controlled that researchers had not previously asked what would happen if it were lowered further. Their starting blood pressure, he said, "was 10 millimeters lower than anyone has studied."

Blood pressure is measured in millimeters of mercury. Current guidelines for most people call for systolic pressure, the pressure when the heart contracts, to be below 140 millimeters, and for diastolic pressure, the pressure when the heart relaxes between beats, to be below 90. When the new study began, its participants had an average systolic pressure of 129 and an average diastolic of 78.

"If you walked in a doctor’s office and your blood pressure was 129 over 78, your doctor would say you have normal blood pressure," Dr. Nissen said.

More research is needed before national guidelines would be changed, but the new study fuels the debate, medical experts said.

"It’s a brick in the wall that is being built in terms of ever lower targets for blood pressure," said Dr. Jeffrey Cutler, a researcher of high blood pressure at the National Heart, Lung, and Blood Institute.

For now, blood pressure experts stress, the blood pressure debate focuses on those at highest risk, like heart patients, who would have to most to gain from drug therapy, and does not apply to healthy people in whom the risk-benefit equation of taking drugs could easily tilt the other way.

"You really can’t generalize to people without pre-existing disease," said Dr. Paul Whelton, senior vice president for health sciences at Tulane University.

The study began with a question, said one of its investigators, Dr. Peter Libby of the Harvard Medical School: "Is average blood pressure optimal for our species?"

It is the same question he and others have been asking about cholesterol levels, and finding that, for cholesterol, the lower the better, at least for people at high risk of heart disease. But most blood pressure studies have focused on reducing high blood pressure to average levels, and finding that such reductions reduced risk of heart attacks and strokes.

In the new study, patients with average blood pressures were randomly assigned to take one of two types of drugs to lower their pressure further – Pfizer’s drug amlodipine, of a class known as calcium channel blockers, or a generic drug, enalapril, of a class known as ACE inhibitors, or to take a placebo.

The two drugs had similar effects on blood pressure, reducing the systolic pressure by an average of five points and diastolic by an average of three points. The number of cardiac events, like heart attacks or stroke or hospitalization for chest pains, was reduced by 31 percent in patients taking amlodipine, and by 15 percent in those taking enalapril.

Among the placebo group, 23 percent, or 151 patients, had such an event during the two-year study as compared to 16.6 percent, or 110 in those taking amlodipine and 20.2 percent, or 136, in those taking enalapril.

Some experts said that they were not sure that amlodipine was better – the study was too small to be that definitive, they said. And both drugs seemed to slow the progression of atherosclerotic plaque.

"To me, that suggests that the major benefit is blood pressure-lowering, no matter how you get there," said Dr. Carl J. Pepine, who is professor and chief of the division of cardiovascular medicine at the University of Florida in Gainesville.

Dr. Thomas Giles, a professor of medicine at Louisiana State University School of Medicine and president of the American Society of Hypertension, said the data should encourage heart disease patients. The study "shows you can stop progress of atherosclerosis and have some regression and you can accomplish that with a reduction of a blood pressure level that some people have considered normal," he said.

The findings also are consistent with studies of populations indicating that risk of heart attacks increases continuously as diastolic blood pressure climbs above 115, Dr. Giles and other researchers said.

"We have taken it as the natural human condition that blood pressures are as high as they are," said Dr. Henry Black, an associate vice president for research at Rush University Medical Center, and an author of the current national guidelines for blood pressure levels. "We have arbitrarily defined ‘normal blood pressure.’ " But that, he said, does not mean that normal is optimal.

Dr. Libby, for one, was astonished by the findings.

"It was an eye-opener," he said, adding that "we have to re-think blood pressure levels for those with heart disease."

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