From healthcentral.com
New research says exposure to certain inhalants could increase the odds of autoimmune conditions
You might not suspect that the air you breathe in could affect your joints or your immune system. But inhaling dust, fumes, and chemical vapours on the job may impact your health in ways far beyond irritating your lungs or causing respiratory issues. Breathing in bad air could also raise your risk of developing rheumatoid arthritis (RA), new research suggests.
A large research review recently published in Arthritis & Rheumatology found that people whose jobs expose them to certain occupational inhalants are at significantly higher risk of developing RA compared to people who aren’t regularly exposed. This new study adds to the growing pile of evidence that inhaling certain substances into the lungs—including silica, asbestos, solvents, pesticides, animal dust, and engine exhaust—may play a key role in triggering RA and other autoimmune diseases.
An Emerging Picture of RA Risk
Scientists don’t fully understand why only some people develop RA, an autoimmune disease in which the immune system attacks the body’s own joints—leading to inflammation, pain, stiffness, and joint damage over time. They do know it involves a combination of genetic, environmental, and lifestyle risk factors, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMSD).
One known risk factor for RA is smoking, according to NIAMSD. This suggests a lung-joint connection that has led researchers to investigate whether breathing in other kinds of harmful particles could also help trigger RA. “There are theories that things we inhale, either work-related or pollution-related, or with smoking cigarettes, may prompt an immune reaction,” says Julianna Desmarais, M.D., an associate professor of medicine in the division of arthritis and rheumatic diseases at the Oregon Health & Science University School of Medicine in Portland, OR.
Some studies have previously suggested a link between RA and breathing in certain types of dust and chemicals—with the most evidence for silica, commonly released into the air in industries like construction and mining. But the results haven’t been conclusive. For this paper, researchers wanted to evaluate the existing body of evidence on a variety of workplace inhalants to get a clear picture of whether they are truly a significant environmental risk factor for RA.
A Clear Signal in the Data
“Our study pulled together decades of global research,” says genetic epidemiologist and study co-author Xia Jiang, Ph.D, an assistant professor in the department of clinical neuroscience at the Karolinska Institute in Stockholm, Sweden, and full professor of epidemiology at the West China School of Public Health at Sichuan University in Chengdu.
The team systematically reviewed 31 studies in total and analysed data pooled from 25 different studies to look at how being exposed to 10 different types of chemicals impacted RA risk. Some of the studies were cohorts (meaning they followed people over time to see who developed RA), while others were case-control studies (comparing inhalant exposures among people with and without RA). The authors also accounted for other known risk factors, like smoking and age.
The results were clear. The review “found strong evidence that breathing in certain dusts and chemicals at work increases a person’s risk of developing rheumatoid arthritis,” says Dr. Jiang.
For seven of the 10 inhalants researchers looked at, there was a significant effect—increasing somebody’s risk of RA anywhere from 20% to 49%, depending on the substance:
Fertilizer: 49% higher risk
Engine exhaust: 45% higher risk
Asbestos: 39% higher risk
Silica: 36% higher risk
Pesticides: 32% higher risk
Solvents: 24% higher risk
Animal dust: 20% higher risk
For many of these agents, there appeared to be a dose effect—meaning that a longer duration or higher intensity of exposure correlated with a greater increase in RA risk. (But the authors note that exposure measurement varied widely across studies).
What surprised the researchers was the variety of inhalants linked to RA. “We expected silica and asbestos to show an effect,” Dr. Jiang says, but “the strength of the connection for some less-studied exposures was striking.” This means that working in industries we might not traditionally think of as particularly dusty or high-risk—like farming and transportation—may increase RA risk, Dr. Jiang explains.
The researchers also identified 25 other inhalants that were associated with an increased risk for RA (such as fungicides, carbon monoxide, welding fumes, and pulp or paper dust). But there weren’t enough studies to include these substances in the analysis.
How Inhalants Might Trigger RA
How could what’s going on in your lungs end up affecting your joints? Scientists think that the lungs may act as a sort of gateway where autoimmune disease begins. “The lung interacts with the outside world in a unique way,” Dr. Desmarais says. Inflammatory dusts and vapours “may lead to an immune reaction that starts in the lungs, but later causes symptoms elsewhere, such as the joints,” Dr. Desmarais says.
“It’s a case of the immune system ‘misfiring’ after being repeatedly triggered in the airways,” Dr. Jiang elaborates. “When you inhale irritating particles, they can cause mild, ongoing inflammation in the lung. In some people, this may confuse the immune system, causing it to attack the body’s own tissues—like the joints—instead of just dealing with the dust.” This may be more likely to happen in people who are already genetically predisposed to RA, Dr. Desmarais adds.
There’s a decent chance that this same process could play a role in other autoimmune diseases. “We already know that smoking is a risk factor for lupus, multiple sclerosis, myositis, and scleroderma,” Dr. Jiang points out. “If inhaled substances can disrupt immune regulation and trigger one autoimmune disease like RA…[they] may provide risk also for these other autoimmune diseases.”
Looking Ahead
Experts would like to see more research into what “dose” of exposure seems to trigger immune responses that lead to RA or other autoimmune diseases. “We need to understand how much and how long exposure is needed to increase risk. Is there a threshold?” says Dr. Jiang. Another big question is how breathing in more than one of these substances could impact RA risk, Dr. Desmarais says, given that people often encounter several dusts or chemicals at once in their workplace.
Researchers also hope to learn how different populations might be affected differently. Future studies could look into whether this exposure threshold varies based on the age or ethnicity of the patient, Dr. Desmarais says—as well as sex, adds Dr. Jiang. “And we need to know how [inhalant exposure] interacts with genetics and lifestyle factors, like smoking,” Dr. Jiang says.
Ultimately, the research into the effects of workplace inhalants will likely expand beyond rheumatoid arthritis—and potentially help answer bigger questions about autoimmunity. “The exposures that we found to be risk factors for RA should also be investigated in other autoimmune diseases,” Dr. Jiang says. And if that turns out to be the case, “workplace air quality might be a broader health concern than previously recognized,” Dr. Jiang says.
https://www.healthcentral.com/news/rheumatoid-arthritis/workplace-air-and-rheumatoid-arthritis-risk
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