Association between long-term exposure to PM2.5 and hypertension: A systematic review and meta-analysis of observational studies

Background: Numerous studies have examined the association between long-term exposure to particulate matter with an aerodynamic diameter of <= 2.5 mu m (PM2.5) and hypertension. However, the results are inconsistent. Objectives: Considering the limitations of previous meta-analyses and the publication of many new studies in recent years, we conducted this meta-analysis to assess the relationship between long-term PM2.5 exposure and the incidence and prevalence of hypertension in a healthy population. Methods: We searched PubMed, Web of Science, Embase, and Scopus for relevant studies published until April 2, 2021 and reviewed the reference lists of previous reviews. A total of 28 observational studies reporting RR or OR with 95% CI for the association between long-term PM2.5 exposure and the risk of hypertension were included. Results: After the sensitivity analysis, we excluded one study with a high degree of heterogeneity, resulting in 27 studies and 28 independent reports. Approximately 42 million participants were involved, and the cases of hypertension in cohort and cross-sectional studies were 508,749 and 1,793,003, respectively. The meta-analysis showed that each 10 mu g/m3 increment in PM2.5 was significantly associated with the risks of hypertension incidence (RR = 1.21, 95% CI: 1.07, 1.35) and prevalence (OR = 1.06, 95% CI: 1.03, 1.09). Subgroup analyses showed that occupational exposure had a significant effect on the association of PM2.5 and hypertension incidence (p for interaction = 0.042) and that the PM2.5 concentration level and physical activity had a noticeable effect on the association of PM2.5 and hypertension prevalence (p for interaction = 0.005; p for interaction = 0.022). Conclusions: A significantly positive correlation was observed between long-term PM2.5 exposure and risks of hypertension incidence and prevalence, and a high PM2.5 concentration resulted in an increased risk of hypertension.