Effect of exposure to PM2.5 on blood pressure: a systematic review and meta-analysis

Background: Comprehensive studies have confirmed that particulate matter air pollution could trigger myocardial infarction, heart failure and reduce heart rate variability; however, its effect on blood pressure (BP) remains controversial. Therefore, we did a systematic review and meta-analysis to investigate the association and its magnitude between exposure to PM2.5 and BP. Methods: The databases of PubMed, Ovid Medline and Embase between 1948 and 15 November 2013 were searched to identify the studies exploring the association between particulate matters (diameter < 2.5 mu m) (PM2.5) and BP. Selection was performed by screening abstracts and titles and then reviewing the full text of potentially eligible studies. We extracted descriptive and quantitative information from each study and used a random-effects model to calculate BP change and 95% confidence interval (95% CI) for each increment of 10 mu g/m(3) in PM2.5. Meta-regression and subgroup analyses were conducted to explore the source of heterogeneity and the impact of possible confounding factors. Results: Of 1028 identified articles, after screening and reviewing in detail, 22 studies were included in our meta-analysis. The overall analysis suggested that BP was positively related to PM2.5 exposure with an elevation of 1.393 mmHg, 95% CI (0.874-1.912) and 0.895 mmHg, 95% CI (0.49-1.299) per 10 mu g/m(3) increase for SBP and DBP, respectively. Long-term exposure showed the strongest associations with BP. And for short-term effect, the largest magnitude was seen at the lag of the previous 5 days average prior to BP measurement. Subgroup analyses yielded consistent results with the overall analyses. Meta-regression of SBP did not identify any significant potential causes of heterogeneity. For DBP, study design, the method of BP monitoring, publication year, study design, study period and sample size were significant modifiers of the relationship between DBP and PM2.5. Conclusion: Exposure to PM2.5 had a statistically significant impact on BP and the magnitude of this effect may have substantially clinical implication.