Global association between ambient air pollution and blood pressure: A systematic review and meta-analysis.

Although numerous studies have investigated the association of ambient air pollution with hypertension and blood pressure (BP), the results were inconsistent. We performed a comprehensive systematic review and meta-analysis of these studies. Seven international and Chinese databases were searched for studies examining the associations of particulate (diameter<2.5 μm (PM2.5), 2.5-10 μm (PM2.5-10) or >10 μm (PM10)) and gaseous (sulfur dioxide (SO2), nitrogen dioxide (NO2), nitrogen oxides (NOx), ozone (O3), carbon monoxide (CO)) air pollutants with hypertension or BP. Odds ratios (OR), regression coefficients (β) and their 95% confidence intervals were calculated to evaluate the strength of the associations. Subgroup analysis, sensitivity analysis, and meta-regression analysis were also conducted. The overall meta-analysis showed significant associations of long-term exposures to PM2.5 with hypertension (OR = 1.05), and of PM10, PM2.5, and NO2 with DBP (β values: 0.47-0.86 mmHg). In addition, short-term exposures to four (PM10, PM2.5, SO2, NO2), two (PM2.5 and SO2), and four air pollutants (PM10, PM2.5, SO2, and NO2), were significantly associated with hypertension (ORs: 1.05-1.10), SBP (β values: 0.53-0.75 mmHg) and DBP (β values: 0.15-0.64 mmHg), respectively. Stratified analyses showed a generally stronger relationship among studies of men, Asians, North Americans, and areas with higher air pollutant levels. In conclusion, our study indicates a positive association between ambient air pollution and increased BP and hypertension. Geographical and socio-demographic factors may modify the pro-hypertensive effects of air pollutants.