Are the effects of blood pressure lowering treatment diminishing?: meta-regression analyses

Abstract Background Previous studies have suggested that the effects of medical interventions tend to diminish over time. We investigated whether the effects of blood pressure lowering treatment on all-cause mortality and stroke have diminished over time. Methods We conducted meta-regression analyses. We extracted the target trials from two recently published comprehensive systematic reviews and meta-analyses. Adopted variables were relative risk (RR) of all-cause mortality and stroke, trial start year, mean age, sample size, baseline systolic blood pressure (SBP), difference in attained SBP reduction between intervention groups and control groups (SBP difference), and regional dummies. We implemented single meta-regressions, in which the dependent variable was the log of RR and the explanatory variable was each of other adopted variables. We also conducted multiple meta-regressions, in which the dependent variable was the log of RR and explanatory variables were all of other adopted variables. Our variable of greatest interest was trial start year. Results The included reviews assessed 85 trials with a total of 343,126 participants. Although trial start year was positively associated with the log of RR in the results of single meta-regressions, it lost significance in multiple meta-regressions for both all-cause mortality and stroke. Conclusions The effects of blood pressure lowering treatment on all-cause mortality and stroke have not diminished over time.