Links between air pollutants and rheumatoid arthritis

Takeaway

• Long-term exposure to ozone and road traffic are associated with increased risk for rheumatoid arthritis (RA), but particulate matter exposures are protective for development of RA, according to a large meta-analysis.
• Gaseous pollutants (nitrogen dioxide, carbon monoxide, and sulfur dioxide) had no association with RA.

Why this matters

• This is the first meta-analysis to investigate the relationship between long-term outdoor air pollutant exposures and RA.

Study design

• Meta-analysis of 8 studies (3 case-control and 5 cohort studies with total of >1,000,000 participants) after a search of PubMed, Embase, and Web of Science.
• Funding: National Natural Science Foundation of China.

Key results

• Ozone was associated with an increased risk for RA (per unit increase in ozone exposure: relative risk [RR], 1.16; 95% CI, 1.15-1.18), as was proximity to road traffic (RR, 1.34; 95% CI, 1.11-1.62).
• 2 types of air pollutants were associated with a decreased risk for RA:
  • Particulate matter 2.5 μm in size (PM_2.5) protected against incident RA (RR, 0.90; 95% CI, 0.81-0.99).
  • Particulate matter 10 μm in size (PM₁₀) protected against onset of seropositive RA (RR, 0.79; 95% CI, 0.69-0.92).
• Long-term exposure to nitrogen dioxide, carbon monoxide, and sulfur dioxide had no association with RA.

Limitations

• Observational designs.