Lowering high blood pressure confers health benefits but how low should it go?

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909106_39531462It s well known that hypertension (HTN), or high blood pressure, is a leading risk factor for heart attack, heart failure, and stroke. At present, a systolic blood pressure (SBP measured when the heart is actively contracting) greater than 140 mm Hg (mercury), combined with a diastolic pressure (DBP measured when the heart is relaxed between beats) greater than 90 mm Hg, is considered to be the lower limit of HTN. Many different drugs are available to help lower blood pressure, and lifestyle changes can also be important in controlling HTN. One important question is how low the target blood pressure should be or how low should it go?

A new report just published in JAMA Internal Medicine provides some information on this question.

Dr. Carlos J. Rodriguez from the Wake Forest School of Medicine in North Carolina and colleagues from several institutions, reported results from the ARIC study (Atherosclerosis Risk in Communities Study). This was a prospective epidemiological study of community-dwelling people. Participants in the study were individuals categorized into 3 groups, depending on their SBP: a control group with SBP less than 120 mm mercury; a second group with a typical BP of 120-139 mmHg, and a group with elevated BP of over 140 mm Hg. A total of nearly 4500 individuals were studied.

After a median follow up period of about 22 years, the investigators found that, compared to those with the lowest SBP, people with elevated SBP had a significantly greater risk of new cardiovascular (CV) problems. However, participants in the two groups with non-elevated SBP did not differ from each other with respect to their risk of CV. Thus, there didn t seem to be any benefit to lowering SPB beyond that of the group with typical SBP of 120-139 mm Hg.

In their discussion, the authors noted our results do not support the notion that SBP control to lower than 120 mm Hg is better. Elevated BP is undoubtedly a risk factor for cardiovascular events, but standard BP control appears to be just as good as lower BP control in preventing HF [heart failure], ischemic stroke, and MI/CHD [heart attack/coronary heart disease]. These results are potentially important, since treatment to a lower BP may have adverse consequences such as orthostatic hypotension, medication adverse effects, and increased health care costs.

Interestingly, this study was published as the FDA is preparing to release guidelines asking the food industry to lower sodium levels in their products. The justification for this is that the government claims that Americans consume too much salt which is associated with increased risk of high blood pressure, strokes and other problems.

ACSH s Dr. Gilbert Ross perspective: This study adds to the argument we have been making all along see e.g. here and here in terms of salt guidelines, especially since these data show that excessive lowering of BP in older folks adds nothing to their long-term health, and may be detrimental. The same thing can be said of excessive reduction in dietary salt intake.