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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteA 2023 analysis of U.S. health survey data found that adults in the highest quartile of measured polycyclic aromatic hydrocarbon (PAH) body burden had 2.2 times the adjusted odds of prevalent, self-reported rheumatoid arthritis (RA) compared with adults in the lowest quartile. That is an association in one cross-sectional sample—not evidence that PAHs doubled a person’s future chance of developing RA or that PAHs cause the disease.
What the study found
Beidelschies and colleagues analyzed National Health and Nutrition Examination Survey (NHANES) data collected from 2007 through 2016. Their 2023 paper in BMJ Open included 21,987 U.S. adults: 1,418 classified as having RA and 20,569 controls who reported no arthritis. Participants were classified as having RA if they said a health professional had told them they had arthritis and then identified the type as rheumatoid arthritis; the analysis did not independently confirm diagnoses.
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Researchers measured PAH metabolites in urine, phthalate or plasticiser metabolites in urine, and volatile organic compounds (VOCs) in blood. In the fully adjusted analysis, the odds of prevalent RA in the highest PAH body-burden quartile were 2.2 times the odds in the lowest quartile (95% confidence interval 1.09–4.2; p=0.028). The models adjusted for age, sex, urine creatinine, body mass index, smoking, race, education, family poverty income ratio, physical activity, and dietary fibre. Read the study in BMJ Open.
The estimate compares groups in the analyzed sample. It is an odds ratio, not a direct estimate of how many people will develop RA, and it should not be read as a forecast for an individual.
Which PAH measure was associated with RA?
The 2.2 estimate concerns a combined PAH body-burden measure, comparing the highest with the lowest quartile. In the analysis of individual toxicants, 1-hydroxynaphthalene was the only one reported as remaining associated with RA in the fully adjusted model: the highest-versus-lowest quartile odds ratio was 1.8 (95% CI 1.1–3.1; p=0.020). This result does not establish that this metabolite, or any specific PAH exposure source, caused RA.
Phthalate or plasticiser metabolites and VOC metabolites were not associated with RA in the fully adjusted models. Those null findings apply to the compounds and measures examined in this study; they do not establish that every chemical in those broad categories is harmless.
Does PAH exposure cause rheumatoid arthritis?
This study cannot answer that. It measured exposure markers and collected disease reports in a cross-sectional analysis, so it cannot show that exposure came before RA. The outcome was self-reported rather than objectively confirmed within the analysis, and blood and urine provide only limited windows into a person’s exposure. The authors identify these as important limitations.
Environmental health professor Roy Harrison, commenting to Chemistry World on 18 May 2023, said the results support the possibility that combustion-related pollutants contribute to RA, while cautioning: “There can be no certainty that PAH are the causal factor, if this relationship is indeed causal.” His interpretation is expert commentary, not proof of a causal link. Read the Chemistry World report.
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How smoking fits into the findings
The authors’ statistical mediation analysis estimated that PAH body burden accounted for 90% of the total effect of smoking on RA in their model. This is a model-based estimate, not proof that PAHs are the biological pathway through which smoking causes RA. After accounting for PAH body burden, the reported smoking association was an odds ratio of 1.4 (95% CI 0.89–2.3; p=0.13); because that confidence interval includes 1, this adjusted result was not statistically significant.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Where PAHs come from—and what this study does not show
PAHs are a class of chemicals associated with burning coal, oil, gas, wood, or tobacco, and with grilling meat. These are possible exposure contexts, not evidence that any one source caused a participant’s RA. The study did not test air purifiers, home air monitors, consumer exposure kits, or other products as ways to prevent or diagnose RA. Its findings do not establish that buying a device or changing one household exposure will prevent the disease.
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How to read the “doubled risk” headline
- What was doubled: adjusted odds of prevalent, self-reported RA when comparing the highest with the lowest PAH body-burden quartile in this sample.
- What was not measured: a person’s prospective risk of developing RA over time.
- What remains uncertain: whether PAHs preceded RA, whether they caused it, and whether a particular PAH source explains the association.
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