Fine particulate matter components and risk of rheumatoid arthritis: A large general Canadian open cohort study.

OBJECTIVE: Exposure to fine particulate matter (PM2.5 ) has been linked to many diseases. However, it remains unclear which PM2.5 chemical components for these diseases, including rheumatoid arthritis (RA), are more harmful. This study aimed to assess potential associations between PM2.5 components and RA, and quantify individual effects of each chemical component on RA risk.

METHODS: 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 end of study (December 2019). Incident RA cases were defined by physician billing and hospitalization discharge diagnostic codes. Average levels of PM2.5 components (ammonium, black carbon, mineral dust, nitrate, organic matter, sea salt, and sulfate) for five years before cohort entry were assigned to subjects based on residential postal codes. A quantile g-computation and a Cox proportional hazard models for time to RA onset were developed for the mixture of PM2.5 components and environmental overall PM2.5 respectively.

RESULTS: We identified 67,676 new RA cases across 130,934,256 person-years. The adjusted hazard ratios for time to RA onset were 1.027 and 1.023 (95% confidence interval: 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 PM2.5 , respectively. Ammonium contributed most to RA onset in the seven components.

CONCLUSIONS: Exposure to PM2.5 components were modestly associated with RA risk. Public health efforts focusing on specific components (e.g., ammonium) may be a more efficient way to reduce RA burden.