Air pollution exposure a risk factor for late-onset rheumatoid arthritis

Exposure to fine particulate matter (PM) appears to contribute to an increased risk of rheumatoid arthritis (RA) incidence after age 65 years, as shown in a study.

The study included 42,152 California Multiethnic Cohort participants aged ≥65 years (42.8 percent Latino) who were enrolled in the Fee for Service component of Medicare. Of these, 2,027 had incident RA. Fine-resolution geospatial model outputs were used to obtain estimates of satellite-based PM_2.5.

RA incidence was lower among participants with higher education, those who were physically active, and those who used menopausal hormones (among women). In contrast, RA incidence was higher among smokers, users of non-steroidal anti-inflammatory drugs (NSAIDs), and those who had high-risk work exposures, namely mining/quarry/cement and paint production industries.

Each 2-μg/m³ increase in PM_2.5 exposure was associated with a 20-percent higher risk of late-onset RA (hazard ratio [HR], 1.20, 95 percent confidence interval [CI], 1.16–1.23). Furthermore, each 10-μg/m³ increase in nitrogen dioxide (NO₂) exposure was associated with a risk increase of 44 percent (HR, 1.44, 95 percent CI, 1.35–1.52).

The associations were more pronounced in African American and Latino participants than in Japanese American and White participants (p<0.05). Additionally, risk of late-onset RA associated with PM_2.5 exposure was higher in men (HR, 1.23, 95 percent CI, 1.15–1.32) than in women (HR, 1.17, 95 percent CI, 1.12–1.21; p=0.06), as well as in those with high-risk work exposure (longest occupation in labor/craftsman work and exposed to ≥10 years in one or more of 13 industries; HR, 1.29, 95 percent CI, 1.18–1.41) than in those without high-risk work exposures (HR, 1.16, 95 percent CI, 1.12–1.21; p=0.04).

More studies are needed to characterize air pollution’s contribution to racial and ethnic disparities in RA risk.