Age-specific associations of Usual Variability of Systolic Blood Pressure with Cardiovascular Disease and Mortality in Patients with Diabetes – A Hong Kong Primary Care Diabetes Cohort Study

Abstract

Objective: The detrimental effects of increased variability in systolic blood pressure (SBP) on the risk of cardiovascular disease (CVD) and mortality remains unclear in patients with type 2 diabetes mellitus (DM). This study aimed to evaluate the age-specific association of usual variability of SBP with CVD and mortality in DM patients. Research Design and Methods: A retrospective cohort study was conducted on 155,982 Chinese primary care diabetic patients aged 45-84 years with no prior diagnosis of CVD at baseline (2008-2010). Usual SBP variability was estimated based on the standard deviations of SBP using a mixed effects model adjusted for regression dilution bias. Age-specific associations (45-54, 55-64, 65-74, 75-84 years) between the usual SBP variability and risk of CVD and mortality were assessed by Cox proportional hazards regression adjusted for patient characteristics. Subgroup analyses were conducted stratified by subject baseline characteristics. Results: After a median follow-up of 9.7 years (16.4 million person-years), there was an overall of 49,816 events, including 34,039 CVD events and 29,211 mortalities. Elevated usual SBP variability and independently usual SBP, were positively and log-linearly associated with a higher risk of CVD and mortality among DM patients, with no evidence of a threshold. Each 5mmHg increase in usual SBP variability was associated with 27% (HR: 1.27 [95% CI 1.23-1.32]), 30% (HR: 1.30[95% CI 1.25-1.35]), and 26% (HR: 1.26[95% CI 1.23-1.30]) increased risk for CVD, all-cause mortality, and their composite, respectively. The significant associations remained consistent among all subgroups, while HRs were raised with males, younger age, smokers and greater number of types of anti-hypertensive medications prescribed. Conclusions: The findings from this population-wide cohort study suggests that SBP variability was strongly related to CVD and mortality with no evidence of a threshold. In addition to aiming for optimal BP control, clinicians should also pay attention to the SBP variability.