Associations between age, cohort, and urbanization with SBP and DBP in China

OBJECTIVE: Little is known about whether large-scale environmental changes, such as those seen with urbanization, are differentially associated with SBP versus DBP, and whether those changes vary by birth cohort. METHODS: We used data from the China Health and Nutrition Survey, a population-based cohort study of Chinese adults (n = 18 754 aged 18-70 years), seen a maximum of seven times from 1991 to 2009. We used hierarchical multivariable linear models to simultaneously estimate SBP and DBP as correlated outcomes over time, accounting for their physiologic, time-varying correlation. Main exposure variables were urbanicity, age, and birth cohort. Over 18 years of modernization, median SBP and DBP increased by 10 and 7 mmHg, respectively. RESULTS: Our hierarchical model results suggest greater temporal increases in SBP and particularly DBP at lower versus higher urbanicity. At the same chronological age, for a 10-year difference in birth cohort (i.e. born in 1980s versus 1970s), the adjusted mean DBP was approximately 3 mmHg higher for the later birth cohort (P < 0.001). Pulse pressure (calculated as model-predicted SBP minus DBP) was also higher at low versus high urbanicity. CONCLUSIONS: These results suggest increased susceptibility of DBP (and thus peripheral vascular resistance) to environmental change, particularly in younger Chinese adults. Because DBP more strongly predicts cardiovascular disease risk in younger adulthood, hypertension-related health burden in China may increase over time.