We’re all familiar with the growing body of evidence linking pollutants in our environment with various chronic conditions, most notably various cancers. But few studies have looked at these toxins’ association with inflammatory conditions such as rheumatoid arthritis (RA), which is thought to be caused by a combination of genetic and lifestyle factors, including smoking and nutrition.
But now, scientists have discovered a link between RA and polycyclic aromatic hydrocarbons (PAF)—chemicals formed from the burning of coal, oil, gas, wood, tobacco, and flame-grilled meat. And their findings indicate that these chemicals seem to account for most of smoking’s impact on the disease.
The Study
Examining the potential role of environmental exposure on RA risk, a team of researchers led by Dr. Michelle Beidelschies of the Center for Functional Medicine at the Cleveland Clinic drew on responses to the US National Health and Nutrition Examination Survey (NHANES) between 2007 and 2016.
The NHANES study included 21,987 adults—1,418 who had rheumatoid arthritis and 20,569 who didn’t. It was designed to test the levels of several toxins in the body, including PAH, which was measured by blood and urine samples.
In analyzing the data, Dr. Beidelschies’ team noted that the odds of developing RA were highest among those in the top 25 percent of PAH levels. After accounting for other potentially influential factors, including dietary fiber, physical activity, smoking, household income, education, age, sex, and weight (BMI), one particular PAH—1-hydroxynaphthalene—was strongly associated with higher odds (80%) of the disease.
Surprisingly, smoking wasn’t associated with heightened rheumatoid arthritis risk after accounting for PAH levels in the body. Further analysis to isolate the influences of PAH and smoking showed that PAH levels accounted for 90 percent of the effect of smoking on RA risk.
Conclusions
As this was an observational study, it can’t determine cause. And the researchers also acknowledge various limitations to their findings. For instance, the study didn’t include measurements of toxins stored in adipose (fat) tissue, nor did it measure bodily levels of heavy metals, which have previously been linked to RA risk.
Regardless, the researchers wrote, “To our knowledge, this is the first study to demonstrate that PAH not only underlie the majority of the relationship between smoking and RA, but also independently contribute to RA. This is important as PAH are ubiquitous in the environment…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.”
The researchers also noted that their results suggest that lower-income people may be more vulnerable to developing RA. “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. In the absence of healthy nutrition and lifestyle behaviors, populations of lower socioeconomic status may also be at greater risk of chronic conditions such as RA due to environmental toxicant exposures.”
