Rheumatoid arthritis is a condition in which the body’s immune system attacks the cells lining the joints, leading to swelling, stiffness, and pain. There are several factors that may increase the likelihood of developing rheumatoid arthritis, including genetics, hormones, and smoking.Although genetics only play a small role in the development of the condition, there is evidence that it may run in families.Additionally, women are more commonly affected than men, which could be due to the effects of the hormone estrogen, although this has not been conclusively proven. Smoking has also been linked to an increased risk of developing rheumatoid arthritis.Now new research published in the open-access journal BMJ Open has suggested that exposure to polycyclic aromatic hydrocarbons (PAH) in the environment may also be strongly linked to the risk of developing rheumatoid arthritis.Several studies suggest that certain chemicals produced by the burning of coal, oil, gas, wood, and tobacco, as well as by flame-grilling food, may be responsible for most of the increased risk of disease associated with smoking.While there is growing evidence linking various environmental toxins to a range of long-term health issues, few studies have explored their potential impact on inflammatory conditions like rheumatoid arthritis, which are believed to result from a complex interplay of factors including genetics, age, lifestyle, and environmental exposure.To investigate this issue, researchers analyzed data from the US National Health and Nutrition Examination Survey (NHANES) between 2007 and 2016, looking for possible links between environmental exposures and the risk of developing rheumatoid arthritis.NHANES, which stands for the National Health and Nutrition Examination Survey, is a comprehensive study that evaluates various harmful substances, including polycyclic aromatic hydrocarbons (PAH), phthalates (PHTHTEs), and volatile organic compounds (VOCs), which are commonly found in consumer products, cleaning agents, paints, and pesticides. The study also collects data related to health, nutrition, lifestyle behaviors, and the environment.This study involved 21,987 adult participants, of which 1418 had rheumatoid arthritis while 20,569 did not. The researchers collected blood and urine samples from 7090 participants to measure the total amount of PAH in the body, 7024 participants for PHTHTEs, and 7129 participants for VOCs.The findings revealed that the odds of developing rheumatoid arthritis were significantly higher in those individuals who had higher levels of bodily PAH, regardless of whether or not they were current or former smokers. Participants in the top 25% of bodily PAH levels had the highest odds of developing rheumatoid arthritis.After taking into consideration potentially influential factors such as dietary fiber intake, physical activity, household income, educational attainment, age, sex, and weight (BMI), the results indicated that only one PAH, specifically 1-hydroxynaphthalene, was strongly linked to an 80% increase in the likelihood of developing the disease.On the other hand, PHTHTE and VOC metabolites did not exhibit a heightened risk of the disease after accounting for the same potentially influential factors.Interestingly, smoking was not found to be associated with an increased risk of rheumatoid arthritis, even after taking PAH levels in the body into account.Further analysis was conducted to separate the effects of PAH and smoking, which revealed that the level of PAH in the body accounted for 90% of the overall effect of smoking on the risk of developing rheumatoid arthritis.It is important to clarify that the study being discussed is an observational one, which means that it cannot establish causation between the variables being studied.The researchers themselves have also noted several limitations to their findings, such as the lack of measurements of environmental toxicants in adipose tissue and heavy metal levels, which have been linked to an increased risk of rheumatoid arthritis.Additionally, it should be noted that cigarettes are a significant source of heavy metal cadmium, which can potentially contribute to the development of rheumatoid arthritis.But, according to the author: “To our knowledge, this is the first study to demonstrate that PAH not only underlie the majority of the relationship between smoking and [rheumatoid arthritis], but also independently contribute to [it].“This is important as PAH are ubiquitous in the environment, derived from various sources, and are mechanistically linked by the aryl hydrocarbon receptor to the underlying pathophysiology of [rheumatoid arthritis].“While PAH levels tend to be higher in adults who smoke…other sources of PAH exposure include indoor environments, motor vehicle exhaust, natural gas, smoke from wood or coal burning fires, fumes from asphalt roads, and consuming grilled or charred foods.“This is pertinent as households of lower socioeconomic status generally experience poorer indoor air quality and may reside in urban areas next to major roadways or in high traffic areas.”According to their suggestions, it is possible that these individuals are especially susceptible and at a higher risk.Source: 10.1136/bmjopen-2022-071514Image Credit: Getty

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