New research suggests that a person’s risk of developing rheumatoid arthritis is strongly linked to their environmental exposure to polycyclic aromatic hydrocarbons (PAH). PAH are chemicals that are formed from burning coal, oil, gas, wood or tobacco, as well as from flame-grilling meat and other foods.
The study also indicates that PAH account for most of the impact smoking has on the risk of developing the disease.
The research drew on responses to the US National Health and Nutrition Examination Survey (NHANES) between 2007 and 2016, evaluating a wide variety of toxicants, including PAH, chemicals used in the manufacture of plastics and various consumer products, and volatile organic compounds (VOCs). The study included 21,987 adults, 1,418 of whom had rheumatoid arthritis and 20,569 of whom did not.
Blood and urine samples were taken to measure the total amount of PAH in the body. The odds of rheumatoid arthritis were highest among those in the top 25% of bodily PAH levels, irrespective of whether or not they were former or current smokers.
After accounting for other factors, only one PAH was found to be strongly associated with higher odds (80%) of the disease. Somewhat surprisingly, however, smoking was not found to be associated with heightened rheumatoid arthritis risk after accounting for PAH levels in the body. Further analysis showed that bodily PAH level accounted for 90% of the total effect of smoking on rheumatoid arthritis risk.
The study acknowledges that it is observational, and cannot determine cause. The researchers also acknowledge various limitations to their findings, including that measurements of environmental toxicants in fat tissue were not available, and heavy metal levels which have previously been linked to rheumatoid arthritis risk were not measured.
Despite this, the researchers suggest that the ubiquity of PAH in the environment, and the fact that 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, make people particularly vulnerable to the negative impact of environmental exposure to PAH.