Relationship Between Cardiovascular Disease and Hypertension via Blood Pressure Curve
The relationship between blood pressure and cardiovascular disease follows a continuous, log-linear curve with no threshold—meaning cardiovascular risk increases progressively starting from blood pressure levels as low as 115/75 mmHg, with each 20 mmHg increase in systolic pressure or 10 mmHg increase in diastolic pressure doubling the risk of death from stroke, heart disease, or other vascular disease. 1
The Continuous Risk Curve
The blood pressure-cardiovascular disease relationship demonstrates several critical characteristics:
No threshold exists: Cardiovascular mortality increases progressively throughout the entire range of blood pressure, including the prehypertensive range (120-139/80-89 mmHg), with approximately 15% of blood pressure-related deaths from coronary heart disease occurring in individuals with blood pressure in this range. 1
Log-linear progression: In a meta-analysis of 61 prospective studies involving 958,074 adults, the risk of CVD increased in a log-linear fashion from systolic blood pressure levels <115 mmHg to >180 mmHg and from diastolic blood pressure levels <75 mmHg to >105 mmHg. 1
Quantifiable risk increments: Each 20 mmHg higher systolic blood pressure and 10 mmHg higher diastolic blood pressure are each associated with a doubling in the risk of death from stroke, heart disease, or other vascular disease. 1
Blood Pressure Categories and Cardiovascular Risk Gradient
The 2017 ACC/AHA guidelines categorize blood pressure based on this continuous risk relationship:
Normal (<120/<80 mmHg): Baseline reference risk 1
Elevated (120-129/<80 mmHg): Hazard ratios for CHD and stroke range between 1.1 and 1.5 compared to normal blood pressure 1
Stage 1 Hypertension (130-139/80-89 mmHg): Hazard ratios for CHD and stroke range between 1.5 and 2.0 compared to normal blood pressure 1
Stage 2 Hypertension (≥140/≥90 mmHg): Substantially elevated risk, well-established in clinical trials 1
Population-Level Impact
The high prevalence of hypertension combined with this continuous risk relationship creates enormous population burden:
Leading cause of death: In 2010, high blood pressure was the leading cause of death and disability-adjusted life years worldwide. 1
Attributable mortality: In the United States, hypertension accounted for more CVD deaths than any other modifiable CVD risk factor and was second only to cigarette smoking as a preventable cause of death for any reason. 1
Event attribution: More than 50% of deaths from coronary heart disease and stroke occurred among individuals with hypertension in a follow-up study of 23,272 U.S. NHANES participants. 1
Population-attributable risk: In the ARIC study, 25% of cardiovascular events (CHD, coronary revascularization, stroke, or heart failure) were attributable to hypertension. 1
Age-Related Modifications of the Curve
The blood pressure-CVD relationship varies by age in important ways:
Relative vs. absolute risk: Although the relative risk of incident CVD associated with higher blood pressure is smaller at older ages, the absolute risk increase is larger in older persons (≥65 years) given their higher baseline absolute risk of CVD. 1
Systolic predominance with aging: After age 60, systolic blood pressure continues to rise while diastolic blood pressure typically plateaus or decreases, making isolated systolic hypertension the most common form in older adults. 2
Consistent gradient across ages: The risk gradient was consistent across subgroups defined by sex and race/ethnicity, though attenuated but still present among older adults. 1
Systolic vs. Diastolic Components
The curve differs for systolic versus diastolic pressure:
Systolic predominance: Higher systolic blood pressure has consistently been associated with increased CVD risk after adjustment for diastolic blood pressure. 1
Diastolic independence unclear: After consideration of systolic blood pressure through adjustment or stratification, diastolic blood pressure has not been consistently associated with CVD risk. 1
Clinical prioritization: Systolic blood pressure (especially) and diastolic blood pressure are prioritized because of the robust evidence base in both observational studies and clinical trials and their ease of measurement in practice settings. 1
Treatment Implications from the Curve
The continuous nature of the curve supports aggressive blood pressure reduction:
Lower targets beneficial: Network meta-analysis of 42 trials including 144,220 patients showed linear associations between mean achieved systolic blood pressure and risk, with the lowest risk at 120-124 mmHg. 3
Quantified treatment benefit: Randomized groups achieving systolic blood pressure of 120-124 mmHg had a hazard ratio for major cardiovascular disease of 0.71 compared with those achieving 130-134 mmHg, and 0.58 compared with 140-144 mmHg. 3
Blood pressure reduction itself is protective: It is blood pressure reduction, not some other pharmacologic property of drugs, that is largely responsible for cardiovascular benefits, as the largest and most consistent outcome benefit has been reduction in stroke risk, with regular reductions also seen in myocardial infarction and cardiovascular mortality. 4, 5
The J-Curve Controversy
Important caveat: While the observational relationship is continuous and linear, some evidence suggests a J-curve may exist at very low blood pressure levels, particularly for diastolic pressure:
Diastolic J-curve: There is increased risk of coronary events below a diastolic blood pressure of 60-70 mmHg, with more compelling evidence for a J-curve between diastolic blood pressure and coronary events specifically. 6
Systolic J-curve less clear: The presence of a systolic J-curve is less clear, and some high-risk persons may actually benefit from systolic levels down to 120 mmHg. 6
Observational vs. trial data: Contemporary observational studies consistently demonstrate a blood pressure J-curve with thresholds often close to intensive treatment targets, though randomized trials like SPRINT support more intensive reduction. 6
Potential confounding: Low blood pressure could be a symptom rather than a cause of disease, especially in patients with recently diagnosed coronary artery disease, those ≥65 years, and those with pulse pressure >60 mmHg. 7