Do other cardiovascular risk factors influence the impact of age on the association between blood pressure and mortality? The MORGAM Project

Objective: To investigate age-related shifts in the relative importance of SBP and DBP as predictors of cardiovascular mortality and all-cause mortality and whether these relations are influenced by other cardiovascular risk factors. Methods: Using 42 cohorts from the MORGAM Project with baseline between 1982 and 1997, 85 772 apparently healthy Europeans and Australians aged 19-78 years were included. During 13.3 years of follow-up, 9.2% died (of whom 7.2% died due to stroke and 21.1% due to coronary heart disease, CHD). Results: Mortality risk was analyzed using hazard ratios per 10-mmHg/5-mmHg increase in SBP/DBP by multivariate-adjusted Cox regressions, including SBP and DBP simultaneously. Because of nonlinearity, SBP and DBP were analyzed separately for blood pressure (BP) values above and below a cut-point wherein mortality risk was the lowest. For the total population, significantly positive associations were found between stroke mortality and SBP [hazard ratio = 1.19 (1.13-1.25)] and DBP at least 78 mmHg [hazard ratio = 1.08 (1.02-1.14)], CHD mortality and SBP at least 116 mmHg [1.20 (1.16-1.24)], and all-cause mortality and SBP at least 120 mmHg [1.09 (1.08-1.11)] and DBP at least 82 mmHg [1.03 (1.02-1.05)]. BP values below the cut-points were inversely related to mortality risk. Taking into account the age x BP interaction, there was a gradual shift from DBP (19-26 years) to both DBP and SBP (27-62 years) and to SBP (63-78 years) as risk factors for stroke mortality and all-cause mortality, but not CHD mortality. The age at which the importance of SBP exceeded DBP was for stroke mortality influenced by sex, cholesterol, and country risk. Conclusion: Age-related shifts to the superiority of SBP exist for stroke mortality and all-cause mortality, and for stroke mortality was this shift influenced by other cardiovascular risk factors.