Systolic blood pressure and mortality

Area of Science:

• Cardiology
• Public Health
• Biostatistics

Background:

• Current hypertension guidelines use a 140 mm Hg systolic blood pressure threshold for all adults.
• Recommendations from WHO and International Society of Hypertension suggest lower normal (130 mm Hg) and optimal (120 mm Hg) pressures.
• These guidelines assume a strictly increasing relationship between systolic blood pressure and mortality, largely based on the Framingham study.

Purpose of the Study:

• To re-evaluate Framingham study data to determine if cardiovascular and overall mortality risk is strictly dependent on systolic blood pressure or if a threshold exists.
• To challenge the assumption of a linear, increasing risk model for systolic blood pressure and mortality.

Main Methods:

• Utilized logistic splines to model the relationship between systolic blood pressure and mortality risk (cardiovascular and all-cause).
• Employed age-specific and sex-specific rates.
• Tested for independence of slope parameters from age and sex, employing a reduced model with common slopes for a non-conventional logistic model.

Main Results:

• The Framingham data rejected the conventional linear logistic model.
• Neither all-cause nor cardiovascular mortality showed a strictly increasing dependence on systolic blood pressure.
• Risk was independent of systolic blood pressure below a specific age- and sex-dependent threshold (around the 70th percentile), sharply increasing above the 80th percentile.

Conclusions:

• The Framingham data contradict the notion that lower systolic blood pressure universally implies lower risk.
• The 140 mm Hg hypertension cut-off is not universally applicable due to age- and sex-dependent risk thresholds.
• A significant portion of the population currently considered at increased risk may not be, based on these findings.