Exposure to nitrogen oxides, particulate matter increase risk for autoimmune disease
Key takeaways:
- Exposure to nitrogen oxides increased risks for rheumatoid arthritis, Sjögren’s and systemic lupus erythematosus.
- PM2.5 and PM10 boosted ulcerative colitis and psoriasis risks, respectively.
Exposure to various air pollutants, such as PM2.5 and nitrogen oxides, increases the risk for several autoimmune diseases, including psoriasis, lupus and rheumatoid arthritis, according to data published in Scientific Reports.
“Although a large number of studies have shown that air pollution is strongly associated with the risk of [autoimmune diseases], there are often contradictions between different studies,” Ming Zhang, of the First Affiliated Hospital of Xi’an Jiaotong University, in China, and colleagues wrote. “Therefore, there is still a lack of crucial evidence to support the causal relationship between the two.”
So far, observational studies have been hampered by confounding factors and reverse causality, while randomized controlled trials face the usual ethical and practical considerations, they added.
To assess the link between air pollutants and autoimmune disease while attempting to avoid those limitations, Zhang and colleagues conducted a Mendelian randomization study, which examines “genetic variations closely associated with exposure to examine causal relationships between exposure and outcome,” they wrote.
The researchers first performed a two-sample Mendelian randomization study investigating the genetic causality of five air pollutants (PM2.5, PM2.5-10, PM10, nitrogen dioxide and nitrogen oxides) with nine autoimmune diseases. These included RA, systemic lupus erythematosus, Crohn’s disease, multiple sclerosis, systemic sclerosis, type 1 diabetes, ulcerative colitis, psoriasis and ankylosing spondylitis.
“Subsequently, in order to investigate whether the impact of air pollution on [autoimmune diseases] is mediated by common risk factors associated with [autoimmune diseases], we conducted a two-step [Mendelian randomization] analysis,” the researchers wrote.
Data on genetic associations with air pollutants was drawn from large-scale genome-wide association studies in the U.K. Biobank. The researchers investigated causal effects using primarily random-effects inverse variance weighting.
According to the results, the odds of developing several autoimmune diseases rose with exposure to nitrogen oxides, including rheumatoid arthritis (OR = 1.47; 95% CI, 1.01-2.14), Sjögren’s disease (OR = 2.29; 95% CI, 1.08-4.89) and SLE (OR = 7.26; 95% CI, 2.25-23.4).
The mediation analyses demonstrated that, in the relationship between nitrogen oxides and RA, BMI mediated 6% (95% CI, 1-10) of the results, while smoking mediated 9% (95% CI, 2-17).
In terms of particulate matter, PM2.5 was linked to an increased risk for ulcerative colitis (OR = 1.68; 95% CI, 1.05-2.68), while PM10 increased the risk for psoriasis (OR = 1.34; 95% CI, 1.02-1.76). However, there was a negative causal relationship between PM2.5-10 and systemic sclerosis (OR = 0.29; 95% CI, 0.1-0.9).
According to the researchers, the mechanisms linking air pollution to the development of autoimmune diseases are unclear, but may involve “immune dysregulation, oxidative stress and epigenetic changes.” They added that their Mendelian randomization design “can only provide preliminary assessments” of these relationships, and noted that the potential for bias due to horizontal pleiotropy “cannot be completely ruled out.”
“Our findings emphasize the importance of improving air pollution to reduce the risks of various [autoimmune diseases], providing valuable insights for policymakers, environmental organizations and health care professionals,” Zhang and colleagues wrote.
Collapse