Polycyclic aromatic hydrocarbons and risk of rheumatoid arthritis: a cross-sectional analysis of the National Health and Nutrition Examination Survey, 2007–2016

OBJECTIVE: While there are several well-established environmental risk factors for rheumatoid arthritis (RA), a paucity of evidence exists linking environmental toxicants with RA prevalence. We aimed to examine the associations between various environmental toxicants and RA among adults in the U.S. general population while adjusting for non-heritable risk factors. DESIGN: Cross-sectional study. SETTING: National Health and Nutrition Examination Survey conducted from 2007 to 2016. PARTICIPANTS: The study included 21 987 adult participants (no RA: 20 569; RA: 1418). Participants were excluded (n=7214) if they did not answer questions related to self-reporting of RA, had another or unknown type of arthritis, or did not have interview or biospecimen data. PRIMARY AND SECONDARY OUTCOME MEASURES: Association between individual toxicants and body burden scores for polycyclic aromatic hydrocarbons (PAH), phthalates and plasticisers (PHTHTEs) metabolites or volatile organic compounds (VOCs) and participant self-reported RA based on multivariable logistic regression models while adjusting for age, sex, urine creatinine, body mass index, smoking, race, education, family poverty income ratio, any vigorous or moderate activity and dietary fibre. RESULTS: While increased prevalence of RA was observed in participants with the highest quartile of various individual PAHs, only 1-hydroxynaphthalene (OR: 1.8 (1.1 to 3.1); p=0.020) remained associated in a fully adjusted model. PAH body burden was found to be associated with RA (Q4 vs Q1, OR: 2.2 (1.09 to 4.2); p=0.028) in a fully adjusted model. Interestingly, after accounting for PAH body burden, smoking was not associated with RA (OR: 1.4 (0.89 to 2.3); p=0.13). A mediation analysis demonstrated that PAH body burden accounted for 90% of the total effect of smoking on RA. PHTHTE and VOC metabolites were not associated with RA in fully adjusted models. CONCLUSIONS AND RELEVANCE: PAHs are associated with RA prevalence, mediate the majority of the effects of smoking on RA, and are associated with RA independent of smoking status.