Trajectories of Blood Pressure Elevation Preceding Hypertension Onset: An Analysis of the Framingham Heart Study Original Cohort

Abstract

Importance: Given that hypertension remains a leading risk factor for chronic disease globally, there are substantial ongoing efforts to define the optimal range of blood pressure (BP).

Objective: To identify a common threshold level above which BP rise tends to accelerate in progression toward hypertension.

Design, setting, and participants: This longitudinal, community-based epidemiological cohort study of adults enrolled in Framingham, Massachusetts, included 1252 participants (mean [SD] age, 35.3 [2.7] years) from the Framingham Original Cohort, of whom 790 (63.1%) were women. Each participant contributed up to 28 serial examinations of standardized resting BP measurements between 1948 and 2005.

Exposures: Age and systolic BP.

Main outcomes and measures: Via a segmented mixed model, we identified significant change points in the association between advancing age and increasing systolic BP among individuals categorized by their age at hypertension onset.

Results: Individuals maintained a relatively stable resting systolic BP level prior to hypertension onset. Systolic BP level began to rise at a more rapid rate after reaching a level of 123.2 mm Hg (95% CI, 122.7-130.1 mm Hg) in people with onset at 40 to 49 years; 122.0 mm Hg (95% CI, 120.3-123.9 mm Hg) in those with onset between 50 and 59 years, 124.9 mm Hg (95% CI, 120.2-127.9 mm Hg) in those with onset between 60 and 69 years, and 120.5 mm Hg (95% CI, 118.0-123.2 mm Hg) in those with onset between 70 and 79 years (P = .29 for between-group heterogeneity).

Conclusions and relevance: We observed that individuals in the community generally maintained a systolic BP of less than 120 to 125 mm Hg, above which systolic BP increased at a relatively rapid rate toward overt hypertension. This trend was consistent whether the hypertension manifested earlier or later in life. Thus, a resting systolic BP that chronically exceeds the range of approximately 120 to 125 mm Hg may represent an important threshold of underlying vascular remodeling and signal incipient hypertension irrespective of age. Further investigations are needed to unravel the sequence of hemodynamic and vascular changes occurring prior to hypertension onset.

Figure 1.. Competing Conceptual Frameworks of Hypothetical Blood Pressure Trajectories Preceding Hypertension

Figure 2.. Observed Blood Pressure Trajectories Preceding Hypertension in the Framingham Heart Study Original Cohort

Longitudinal analyses, including a piecewise segmented linear model (solid lines), identified systolic blood pressure change points (labeled) for participants across categories of hypertension onset age. Also shown are restricted cubic splines (dashed lines), with 95% confidence intervals derived from associating age with systolic blood pressure, without modeling to identify change points; all splines and regression lines are truncated at the 2.5th and 97.5th percentiles of the age distribution for each hypertension age of onset category.