Rheumatoid Arthritis results from interactions between genes and the environment and is preceded by a preclinical stage characterized by autoantibodies. By encouraging pulmonary immune activation, smoking and other inhaled exposures raise the risk of RA, particularly in genetically predisposed people. Given that autoimmunity frequently starts years before symptoms appear, early environmental exposures may be crucial.
There is growing evidence that the lung is involved early in the pathophysiology of RA, suggesting that childhood exposure to microbial or inhaled variables, especially in rural areas, may affect the development of RA in the future. Using information from a sizable prospective cohort, this study evaluated the relationship between childhood exposure to farm animals and pets and the likelihood of having RA as an adult.
In this study 698 incident instances of RA were found and confirmed among the 78,473 women from the Etude Epidémiologique au Québec des femmes de la Mutuelleâtre de l'Education Nationale cohort. The participants self-reported their age of first exposure to farm animals and household pets (cats, dogs), using predetermined categorization options (e.g., never, <1 year, 1–2 years, etc.). Cox models were used to estimate HRs, and directed acyclic graphs were used to choose confounders.
Regardless of smoking status, early exposure to pets (cats or dogs) between the ages of one and two years was linked to a decreased risk of RA (adjusted HR (aHR) 0.57, 95% CI 0.34 to 0.95) when compared to no exposure. However, neither younger (less than a year) nor later ages showed any correlation with pet exposure.
On the other hand, regardless of age at exposure, childhood exposure to farm animals (cows, sheep, and pigs) was marginally linked to an increased risk of RA (aHR 1.26, 95% CI 1.00 to 1.59). Overall, RA risk may be influenced by the kind and timing of childhood animal exposure, with a potential critical window occurring between the ages of one and two.
Source:
Dusser, P., Nguyen, Y., Perrin, C., Frénoy, P., Mariette, X., Boutron-Ruault, M.-C., Varraso, R., Severi, G., Salliot, C., & Seror, R. (2025). Early-life animal and farming exposures and the risk of rheumatoid arthritis: findings from the E3N French cohort study. RMD Open, 11(4), e005954. https://doi.org/10.1136/rmdopen-2025-005954
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