The effect of air pollution on systemic lupus erythematosus: A systematic review and meta-analysis

Background Systemic lupus erythematosus (SLE) is an autoimmune disease resulting from impaired inflammatory responses. Given the role of air pollution on increasing inflammatory mediators, thus, we aimed to systematically review and meta-analyze evidence regarding an association between short-term exposure to air pollution and SLE onset, activity, and hospitalization. Methods Electronic databases including Web of Science, PubMed, Scopus, and Embase were searched for all published articles until July 5, 2021. Newcastle Ottawa Scale (NOS) checklist was used to assess the quality of individual studies. Relevant demographic data and the intended results of the selected studies were extracted, and their adjusted risk ratios (RRs) were pooled using random and fixed effect analysis based on the heterogeneity index. Findings Twelve studies were entered in our systematic review, and finally, six publications were enrolled in meta-analysis. Overall, Meta-analysis showed no significant association between an increase of PM2.5 on the third day and SLEDAI score with pooled adjusted RR of 1.212 (95% CI, 0,853-1.721), p-value = 0.284. However, there was a positive relationship between 6 days increase of Particulate matter (PM) 2.5 and the systemic lupus erythematosus disease activity Index (SLEDAI) score (pooled adjusted RR 1.112; 95% CI, 1.005-1.231), p-value = 0.040. There was no significant association between carbon monoxide (CO), nitrogen dioxide (NO2), PM2.5, and PM10 increase in the air and hospitalization of SLE patients with pooled RR of 1.021 (95% CI, 0,986-1.1.057), p-value = 0.249, 1.034 (95% CI, 0.996-1.068); p-value = 0.079, 1.042 (95% CI, 0.994-1.092); p-value = 0.084 and 1.004 (95% CI, 0.996-1.013); p-value = 0.323, respectively. Also, analysis showed a significant relation between ozone (O-3) increase and hospitalization with a pooled RR of 1.076 (95% CI, 1.009-1.147); p-value = 0.025. Finally, analysis of SO2 increase and risk of hospitalization demonstrated no significant relationship with the pooled RR of 1.011; (95% CI, 0.962-1.062), p-value = 0.0.671. Conclusion Our findings prove that PM2.5 was associated with increased SLE risk. We also showed that only O-3 was associated with increased hospital admissions of SLE patients.