Fine Particulate Matter Components and Risk of Rheumatoid Arthritis: A Large General Canadian Open Cohort Study

Exposure to fine particulate matter (PM_2.5) has been linked to many diseases. However, it remains unclear which PM_2.5 chemical components for these diseases, including rheumatoid arthritis (RA), are more harmful. This study aimed to assess potential associations between PM_2.5 components and RA and quantify the individual effects of each chemical component on RA risk.

An open cohort of 11,696,930 Canadian adults was assembled using Ontario administrative health data from January 2007 onward. Individuals were followed until RA onset, death, emigration from Ontario, or the end of the study (December 2019). Incident RA cases were defined by physician billing and hospitalization discharge diagnostic codes. The average levels of PM_2.5 components (ammonium, black carbon, mineral dust, nitrate, organic matter, sea salt, and sulfate) for 5 years before cohort entry were assigned to participants based on residential postal codes. A quantile g-computation and Cox proportional hazard models for time to RA onset were developed for the mixture of PM_2.5 components and environmental overall PM_2.5, respectively.

We identified 67,676 new RA cases across 130,934,256 person-years. The adjusted hazard ratios for the time to RA onset were 1.027 and 1.023 (95% confidence intervals 1.021-1.033 and 1.017-1.029) per every decile increase in exposures to all seven components and per 1 μg/m³ increase in the overall PM_2.5, respectively. Ammonium contributed the most to RA onset in the seven components.

Exposure to PM_2.5 components was modestly associated with RA risk. Public health efforts focusing on specific components (eg, ammonium) may be a more efficient way to reduce RA burden.