Risk of developing rheumatoid arthritis doubled by exposure to polycyclic aromatic hydrocarbons | Research

Exposure to polycyclic aromatic hydrocarbons (PAHs), which are formed during combustion, could significantly increase the risk of developing rheumatoid arthritis (RA), whether or not they smoke. The authors said the findings confirmed and expanded the limited evidence for the relationship between PAHs and RA.

PAHs are a class of ubiquitous chemicals formed when coal, oil, gas and wood are burned or when cooking meat. Tobacco is also a known source of PAHs.

The cross-sectional study aimed to explore the association between PAHs in smokers and non-smokers and the prevalence of RA while controlling for important confounders such as age, sex and body mass index. bodily. It included more than 21,000 adult participants, including 1,418 with rheumatoid arthritis, using data collected between 2007 and 2016 by the US National Health and Nutrition Examination Survey.

Associations between individual toxicants – including phthalate and plasticizer metabolites or volatile organic compounds (VOCs), as well as PAHs – and RA were assessed. A body burden score was established for each participant, via blood and urine samples, which provided a measure of their exposure to these chemicals via the resulting metabolites.

When comparing those in the highest quartile for PAH body burden with those in the lowest quartile, the odds of developing RA more than doubled. After adjusting for confounding factors, a single PAH, 1-hydroxynaphthalene, was associated with an increased risk of developing RA. In contrast, phthalate, plasticizer, and VOC metabolites were not associated with RA in the fully adjusted models.

The researchers also analyzed whether body PAH burden influenced the relationship between smoking and rheumatoid arthritis. They found that smoking was associated with RA, as well as PAH body burden and PAH body burden was still associated with RA after adjusting for smoking. From this, the authors calculated that body PAH burden accounted for almost 90% of the total effect of smoking on RA. PAH body burden was also significantly associated with RA in non-smokers, but was not significant in the fully adjusted model.

The authors said that, to their knowledge, their study was the first to demonstrate that PAHs not only underlie the majority of the relationship between smoking and RA, but also independently contribute to RA.

“The current study supports and expands the available evidence demonstrating that environmental PAHs are associated with the prevalence of RA in the US population, regardless of smoking status,” the authors write.

Roy Harrisson, a professor of environmental health at the University of Birmingham, says that although the study was “carried out carefully”, it was important not to “over-interpret” the results. “The results show several positive and statistically significant positive associations between self-reported rheumatoid arthritis and several PAH metabolites measured in urine,” he adds. “Such associations were not found with phthalate plasticizers or toluene.”

Harrison adds that study limitations included the lack of an objective determination of disease or diagnosis and small effect sizes for individual metabolites. “My interpretation is that the study supports the likelihood that exposure to combustion-related pollutants is a contributing factor to rheumatoid arthritis.

“There can be no certainty that PAHs are the causative factor, if this relationship is indeed causal,” says Harrison. “However, the results suggest that exposures in the top quartile lead to a doubling of disease risk compared to exposures in the bottom quartile, which is important in terms of public health.”