Causal association between air pollution and autoimmune diseases: a two-sample Mendelian randomization study

In recent years, an increasing number of observational studies have reported the impact of air pollution on autoimmune diseases (ADs). However, no Mendelian randomization (MR) studies have been conducted to investigate the causal relationships. To enhance our understanding of causality, we examined the causal relationships between particulate matter (PM) and nitrogen oxides (NO_x) and ADs.

We utilized genome-wide association study (GWAS) data on PM and NO_x from the UK Biobank in European and East Asian populations. We also extracted integrated GWAS data from the Finnish consortium and the Japanese Biobank for two-sample MR analysis. We employed inverse variance weighted (IVW) analysis to assess the causal relationship between PM and NO_x exposure and ADs. Additionally, we conducted supplementary analyses using four methods, including IVW (fixed effects), weighted median, weighted mode, and simple mode, to further investigate this relationship.

In the European population, the results of MR analysis suggested a statistically significant association between PM_2.5 and psoriasis only (OR = 3.86; 95% CI: 1.89-7.88; P_IVW < 0.00625), while a potential association exists between PM_2.5-10 and vitiligo (OR = 7.42; 95% CI: 1.02-53.94; P_IVW < 0.05), as well as between PM_2.5 and systemic lupus erythematosus (OR = 68.17; 95% CI: 2.17-2.1e+03; P_IVW < 0.05). In East Asian populations, no causal relationship was found between air pollutants and the risk of systemic lupus erythematosus and rheumatoid arthritis (P_IVW > 0.025). There was no pleiotropy in the results.

Our results suggest a causal association between PM_2.5 and psoriasis in European populations. With the help of air pollution prevention and control, the harmful progression of psoriasis may be slowed.