Blood Pressure and Mortality: Joint Effect of Blood Pressure Measures

We examine how combinations of systolic and diastolic blood pressure levels and pulse pressure levels predicted mortality risk. Respondents are those aged over 50 from the Health and Retirement Study (N=10,366) who provided blood pressure measures in 2006/2008. Systolic and diastolic blood pressures were measured three times; and we averaged the three readings. Pulse pressure was calculated as systolic minus diastolic blood pressure. Seven combinations of systolic and diastolic blood pressure (low/normal/high of each) and three levels of pulse pressure (low/normal/high) were used to categorize blood pressure. Over 1 to 10 years of follow-up (average follow-up time of 7.8 years), 2,820 respondents died after blood pressure measurement in 2006/2008. Potential covariates including age, gender, education, BMI, total cholesterol, HbA1c, antihypertensive medication intake and lifetime-smoking pack years were adjusted in Cox proportional hazard models and survival curves. The blood pressure subgroup with low systolic blood pressure (<90 mmHg) and low diastolic blood pressure (< 60 mmHg) had the highest relative risk of mortality (HR=2.34, 95% CI: 1.45-3.80), followed by those with normal systolic blood pressure but low diastolic blood pressure (HR=1.45, 95% CI: 1.17-1.81) among those with cardiovascular conditions at baseline. For those without cardiovascular conditions at baseline, low blood pressure, either systolic or diastolic, was not related to mortality. Those with high levels of both systolic and diastolic blood pressure had a higher risk of mortality than those with both blood pressures normal but no other subgroups with low blood pressure differed from normal/normal in predicting mortality. Pulse pressure did not predict mortality. How high and low blood pressures are related to mortality needs to be examined by jointly looking at systolic and diastolic blood pressure.