Exposure to air pollution and cognitive impairment risk: a meta-analysis of longitudinal cohort studies with dose-response analysis

Background We conducted a meta-analysis to explore the relationship between exposure to air pollution and the risk of cognitive impairment of longitudinal cohort studies. Methods PubMed, Web of Science and Wan Fang databases were searched for relevant articles of longitudinal cohort studies published between January 1950 and September 2019. The pooled relative ratio (RR) and 95% confidence interval (CI) were calculated using the random effect model. Results Ten articles involving 519 247 cases among 12 523 553 participants were included in this meta-analysis. The pooled RR of cognitive impairment per 5 mu g/m(3) increments in exposure to particulate matter <= 2.5 mu m (PM2.5) was 1.08 (95% CI = 1.03, 1.13; I-2 = 82.2%; P-heterogeneity< 0 . 001 ). No association was found between nitrogen dioxide/nitrogen oxide (NO2/NOx) and ozone (O-3) and cognitive impairment. For PM2.5 exposure, in subgroup analysis, the above-mentioned significant positive association was found among studies conducted in population (RRper (5 mu g/m3) = 1.05; 95% CI= 1.01, 1.09; I-2 =57.4%; P-heterogeneity=( )0.016), in North America (RRper (5 mu g/m3) = 1.13; 95% CI =1.01,1.26; I-2 = 86.7%; P-heterogenei(ty) < 0.001) and with follow-up duration >10 years (RRper (5 mu g/m3 )= 1.10; 95% CI =1.03,1.17; I-2 =86.3%; P-heterogeneity < 0.001). Conclusions This meta-analysis suggests that exposure to PM2.5 might increase the risk of cognitive impairment.