Redefining Definition of “Normal” Blood Pressure could Reduce the Number of Americans Labeled as Abnormal by 100 Million

BACKGROUND:
Physicians have traditionally been taught to think of elevated diastolic blood pressure (DBP) as abnormal. Currently, the National Heart, Lung and Blood Institute defines a blood pressure under 120/80 as “normal.” This study examined the independent effects of diastolic and systolic blood pressure (SBP) on mortality – and estimated the number of Americans affected by accounting for these effects in the definition of “normal.” Investigators linked data collected in the first National Health and Nutrition Examination Survey (conducted 1971-1976) to vital status data through 1992 for 13,792 adults aged 25 to 75 years. The main outcome was the observed all-cause mortality rate for a given blood pressure category relative to that for a so-called “normal” blood pressure: less than 120/80. Models were adjusted for demographics, smoking status, BMI, and total cholesterol; separate analyses were performed for individuals younger and older than age 50.

FINDINGS:

• Systolic blood pressure elevations are more important than diastolic blood pressure elevations in individuals older than age 50. The situation was reversed in individuals younger than age 50, in whom DBP was the more important predictor of mortality.
• For individuals older than age 50, the lowest and highest blood pressures were associated with the greatest rates of death. Without adjusting for SBP, the rate of death began to increase at a DBP of 90 or higher; however, adjusting for SBP made the relationship disappear. The mortality rate began to significantly increase at SBP >140 – independent of DBP.
• For individuals younger than age 50, a DBP above 100 was associated with significant increases in mortality, with or without adjustment for SBP.
• The current definition of normal BP (<120/80) leads an estimated 160 million adult Americans to be labeled abnormal. Redefining normal BP as one that does not confer an increased mortality risk (DBP <100 under age 50, SBP <140 over age 50) would reduce that number to less than 60 million.

LIMITATIONS:

• This is an observational study and only measured blood pressure at one point in time.
• This study does not provide data about treatment or quality of life.

IMPLICATIONS:

• Small changes in the definition of normal blood pressure have tremendous impact on the number of Americans classified as hypertensive. These additional patients stand the least to gain from treatment and may be at higher risk for hypotension-related adverse events. Refining the definition of hypertension may reduce the number of patients determined to require treatment, and thereby permit providers to focus their efforts on patients with substantial BP elevations who will benefit most.

AUTHOR/FUNDING INFORMATION:
Drs. Taylor and Wilt are part of HSR&D’s Center for Chronic Disease Outcomes Research in Minneapolis, MN. Dr. Welch is part of the VA Outcomes Group, White River Junction, VT.

Taylor BC, Wilt TJ, and Welch HG. Impact of Diastolic and Systolic Blood Pressure on Mortality: Implications for the Definition of “Normal.” Journal of General Internal Medicine March 15, 2011;e-pub ahead of print.

Embargoed until publication.