How Low Should Your Blood Pressure Be?

By Thomas Lee, M.D.
Content provided by the Faculty of the Harvard Medical School

Blood pressure is increasingly looking like the new cholesterol. Like cholesterol, blood pressure tends to go up as we get older — especially if we are getting fatter at the same time. Also, like high cholesterol, high blood pressure is an important risk factor for heart attacks. And now, just as with cholesterol, evidence is emerging that people with levels of blood pressure that were considered "normal" just a few years ago may be better off if those levels are brought down.

For decades, 120/80 was considered a "normal" blood pressure, sending a message that this was an ideal blood pressure. And readings of 135/88 were "fine." The reality may be that you would be better off if your blood pressure stays below 120/80 and that 135/88 is actually too high.

The first major warning that the old "normal" is not ideal came when the National Heart, Lung and Blood Institute published its new hypertension guidelines in 2004. The guidelines pointed out that the risk of heart attack and stroke increases when systolic blood pressure (the top number) is greater than 115 mmHg and diastolic blood pressure (the bottom number) is greater than 75 mm Hg. For every 20-mm-Hg increase in systolic pressure or 10-mm-Hg increase in diastolic blood pressure, your risk of dying from cardiovascular diseases doubles. Based on this information, the new guidelines defined a large number of people with readings between 120-139 over 80-89 as "prehypertensive," a label that indicates some action is needed, not necessarily drugs, to bring those numbers down.

A lot of physicians thought that the hypertension experts got kind of carried away. However, as happened with cholesterol, research is coming along that strongly suggests the "aggressive" guidelines to be correct.

For example, a study published in 2004 tested two different drugs for hypertension in 1,991 patients with coronary artery disease, all of whom had "normal" blood pressures. The average blood pressure at the beginning of the two-year study was 129/78 mm Hg.

The patients were randomly assigned to get a calcium blocker drug (amlodipine, also known as Norvasc), or an ACE inhibitor (enalapril, also know as Vasotec), or a placebo. Both drugs lowered systolic blood pressures by about 5 mm Hg, and diastolic pressures by about 2.5 mm Hg.

During the two years of follow-up, cardiovascular complications occurred to 23% of the patients who received placebo, compared with just 17% of those who received amlodipine and 20% of those who received enalapril.

Especially interesting were findings on atherosclerosis in the subjects' coronary arteries. The atherosclerosis had progressed in the patients who received placebo, but not in those who had received either blood-pressure-lowering drug.

The study still gets a lot of attention, because it supports the belief that we are not setting our blood-pressure goals low enough. This more aggressive goal may make sense, but we haven't come close to getting the people with diagnosed hypertension, that is, people with readings over 140/90, into range. Some estimates say that two-thirds of people currently diagnosed with hypertension do not have good blood-pressure control.

Today, most people can lower cholesterol to some really low levels using medications without causing significant side effects. This is not so easy when reducing blood pressure. You can only push blood pressure so low before people get light-headed, and perhaps even pass out. Most people start to get symptoms like these when systolic pressure (the top number) goes below 80 to 90. That said, very few patients with hypertension have blood pressures anywhere near this range.

Like cholesterol, the main message is that doctors and patients need to work harder to bring blood pressure under control. Weight loss, regular exercise and a diet rich in fruits and vegetables with less salt make blood-pressure drugs more effective. There are plenty of medication choices. The right drugs are the ones that work for you and that you take every day.

Copyright: Copyright Harvard Health Publications

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High blood pressure, or hypertension, is known as the "silent killer" because: