Air pollution exposure increases the risk of rheumatoid arthritis: A longitudinal and nationwide study

Rheumatoid arthritis (RA) has been associated with inhaled pollutants in several studies, and it is a disease of chronic inflammation. The association between air pollution and the risk of RA remains unclear. Therefore, we conducted this nationwide, retrospective, sex-stratification study to evaluate this association.

We collected data from the Longitudinal Health Insurance Database (LHID), maintained by the Taiwan Bureau of National Health Insurance, and the Taiwan Air Quality-Monitoring Database (TAQMD), released by the Taiwan Environmental Protection Agency. The TAQMD provides the daily concentrations of particulate matter with the aerodynamic diameter <2.5μm (PM2.5) and nitrogen dioxide (NO2) from 74 ambient air quality-monitoring stations distributed all over Taiwan during 1998-2010. The LHID and TAQMD were linked according to the residential areas of insurants and the areas where the air quality-monitoring stations were located. A residential area was defined according to the location of the clinic and hospital that treated acute upper respiratory tract infections. The yearly average air pollutant concentrations were categorized into 4 levels based on quartiles. We evaluated the risk of RA in residents exposed to 4 levels of PM2.5 and NO2 concentrations.

We detected an increased risk of RA in participants exposed to PM2.5 and NO2. Among four quartiles of NO2 concentration, namely Q1, Q2, Q3, and Q4, the adjusted hazard ratios (aHRs) in Q2, Q3, and Q4 compared with that in Q1 were 1.07 (95% confidence interval [CI]=0.76-1.50), 1.63 (95% CI=1.16-2.31),and 1.49 (95% CI=1.05-2.12), respectively. Regarding the PM2.5 concentrations, the aHRs after exposure to the Q2, Q3, and Q4 levels were 1.22 (95% CI=0.85-1.74), 1.15 (95% CI=0.82-1.62), and 0.79 (95% CI=0.53-1.16), respectively.

The results of this nationwide study suggest an increased risk of RA in residents exposed to NO2.