Pollution Levels Linked to Physical and Mental Health Problems

Heidi Splete

March 17, 2022

New studies show that chronic exposure to air pollution is associated with increased risk of autoimmune disease in adults and depression in adolescents.

Other analyses of data have found environmental air pollution from sources such as car exhaust and factory output can trigger an inflammatory response in the body. What's new about a study published in RMD Open is that it explored an association between long-term exposure to pollution and risk of autoimmune diseases, wrote Giovanni Adami, MD, of the University of Verona (Italy) and colleagues.

"Environmental air pollution, according to the World Health Organization, is a major risk to health and 99% of the population worldwide is living in places where recommendations for air quality are not met," said Adami in an interview. The limited data on the precise role of air pollution on rheumatic diseases in particular prompted the study, he said.

To explore the potential link between air pollution exposure and autoimmune disease, the researchers reviewed medical information from 81,363 adults via a national medical database in Italy; the data were submitted between June 2016 and November 2020.

The average age of the study population was 65 years, and 92% were women; 22% had at least one coexisting health condition. Each study participant was linked to local environmental monitoring via their residential postcode.

The researchers obtained details about concentrations of particulate matter in the environment from the Italian Institute of Environmental Protection that included 617 monitoring stations in 110 Italian provinces. They focused on concentrations of 10 and 2.5 (PM10 and PM2.5).

Exposure thresholds of 30 mcg/m3 for PM10 and 20 mcg/m3 for PM2.5 are generally considered harmful to health, they noted. On average, the long-term exposure was 16 mcg/m3 for PM2.5 and 25 mcg/m3 for PM10 between 2013 and 2019.

Overall, 9,723 individuals (12%) were diagnosed with an autoimmune disease between 2016 and 2020.

Exposure to PM10 was associated with a 7% higher risk of diagnosis with any autoimmune disease for every 10 mcg/m3 increase in concentration, but no association appeared between PM2.5 exposure and increased risk of autoimmune diseases.

However, in an adjusted model, chronic exposure to PM10 above 30 mcg/m3 and to PM2.5 above 20 mcg/m3 were associated with a 12% and 13% higher risk, respectively, of any autoimmune disease.

Chronic exposure to high levels of PM10 was specifically associated with a higher risk of rheumatoid arthritis, but no other autoimmune diseases. Chronic exposure to high levels of PM2.5 was associated with a higher risk of rheumatoid arthritis, connective tissue diseases, and inflammatory bowel diseases.

In their discussion, the researchers noted that the smaller diameter of PM2.5 molecules fluctuate less in response to rain and other weather, compared with PM10 molecules, which might make them a more accurate predictor of exposure to chronic air pollution.

The study findings were limited by several factors including the observational design, which prohibits the establishment of cause, and a lack of data on the start of symptoms and dates of diagnoses for autoimmune diseases, the researchers noted. Other limitations include the high percentage of older women in the study, which may limit generalizability, and the inability to account for additional personal exposure to pollutants outside of the environmental exposure, they said.

However, the results were strengthened by the large sample size and wide geographic distribution with variable pollution exposure, they said.

"Unfortunately, we were not surprised at all," by the findings, Adami said in an interview.

"The biological rationale underpinning our findings is strong. Nevertheless, the magnitude of the effect was overwhelming. In addition, we saw an effect even at threshold of exposure that is widely considered as safe," Adami noted.

Clinicians have been taught to consider cigarette smoking or other lifestyle behaviors as major risk factors for the development of several autoimmune diseases, said Adami. "In the future, we probably should include air pollution exposure as a risk factor as well. Interestingly, there is also accumulating evidence linking acute exposure to environmental air pollution with flares of chronic arthritis," he said.

"Our study could have direct societal and political consequences," and might help direct policy makers' decisions on addressing strategies aimed to reduce fossil emissions, he said. As for additional research, "we certainly need multination studies to confirm our results on a larger scale," Adami emphasized. "In addition, it is time to take action and start designing interventions aimed to reduce acute and chronic exposure to air pollution in patients suffering from RMDs."

Consider the Big Picture of Air Quality

The Italian study is especially timely "given our evolving and emerging understanding of environmental risk factors for acute and chronic diseases, which we must first understand before we can address," said Eileen Barrett, MD, of the University of New Mexico, Albuquerque, in an interview.

"I am largely surprised about the findings, as most physicians aren't studying ambient air quality and risk for autoimmune disease," said Barrett. "More often we think of air quality when we think of risk for respiratory diseases than autoimmune diseases, per se," she said.

"There are several take-home messages from this study," said Barrett. "The first is that we need more research to understand the consequences of air pollutants on health. Second, this study reminds us to think broadly about how air quality and our environment can affect health. And third, all clinicians should be committed to promoting science that can improve public health and reduce death and disability," she emphasized.

The findings do not specifically reflect associations between pollution and other conditions such as chronic obstructive pulmonary disease and asthma although previous studies have shown an association between asthma and COPD exacerbations and air pollution, Barrett said.

"Further research will be needed to confirm the associations reported in this study," Barrett said.

More research in other countries, including research related to other autoimmune diseases, and with other datasets on population and community level risks from poor air quality, would be helpful, and that information could be used to advise smart public policy, Barrett added.

Air Pollution's Mental Health Impact

Air pollution's effects extend beyond physical to the psychological, a new study of depression in teenagers showed. This study was published in Developmental Psychology.

Previous research on the environmental factors associated with depressive symptoms in teens has focused mainly on individual and family level contributors; the impact of the physical environment has not been well studied, the investigators, Erika M. Manczak, PhD, of the University of Denver and colleagues, wrote.

In their paper, the authors found a significant impact of neighborhood ozone exposure on the trajectory of depressive symptoms in teens over a 4-year period.

"Given that inhaling pollution activates biological pathways implicated in the development of depression, including immune, cardiovascular, and neurodevelopmental processes, exposure to ambient air pollution may influence the development and/or trajectory of depressive symptoms in youth," they said.

The researchers recruited 213 adolescents in the San Francisco Bay area through local advertisements. The participants were aged 9-13 years at baseline, with an average age of 11 years. A total of 121 were female, 47% were white, 8.5% were African American, 12.3% were Asian, 10.4% were nonwhite Latin, and 21.7% were biracial or another ethnicity. The participants self-reported depressive symptoms and other psychopathology symptoms up to three times during the study period. Ozone exposure was calculated based on home addresses.

After controlling for other personal, family, and neighborhood variables, the researchers found that higher levels of ozone exposure were significantly associated with increased depressive symptoms over time, and the slope of trajectory of depressive symptoms became steeper as the ozone levels increased (P less than .001). Ozone did not significantly predict the trajectory of any other psychopathology symptoms.

"The results of this study provide preliminary support for the possibility that ozone is an overlooked contributor to the development or course of youth depressive symptoms," the researchers wrote in their discussion.

"Interestingly, the association between ozone and symptom trajectories as measured by Anxious/Depressed subscale of the [Youth Self-Report] was not as strong as it was for the [Children's Depression Inventory-Short Version] or Withdrawn/Depressed scales, suggesting that associations are more robust for behavioral withdrawal symptoms of depression than for other types of symptoms," they noted.

The study findings were limited by the use of self-reports and by the inability of the study design to show causality, the researchers said. Other limitations include the use of average assessments of ozone that are less precise, lack of assessment of biological pathways for risk, lack of formal psychiatric diagnoses, and the small geographic region included in the study, they said.

However, the results provide preliminary evidence that ozone exposure is a potential contributing factor to depressive symptoms in youth, and serve as a jumping-off point for future research, they noted. Future studies should address changes in systemic inflammation, neurodevelopment, or stress reactivity, as well as concurrent psychosocial or biological factors, and temporal associations between air pollution and mental health symptoms, they concluded.

Environmental Factors Drive Inflammatory Responses

Peter L. Loper Jr., MD, considers the findings of the Developmental Psychology study to be unsurprising but important – because air pollution is simply getting worse.

"As the study authors cite, there is sufficient data correlating ozone to negative physical health outcomes in youth, but a paucity of data exploring the impact of poor air quality on mental health outcomes in this demographic," noted Loper, of the University of South Carolina, Columbia, in an interview.

"As discussed by the study researchers, any environmental exposure that increases immune-mediated inflammation can result in negative health outcomes. In fact, there is already data to suggest that similar cytokines, or immune cell signalers, that get released by our immune system due to environmental exposures and that contribute to asthma, may also be implicated in depression and other mental health problems," he noted.

"Just like downstream symptom indicators of physical illnesses such as asthma are secondary to immune-mediated pulmonary inflammation, downstream symptom indicators of mental illness, such as depression, are secondary to immune-mediated neuroinflammation," Loper emphasized. "The most well-characterized upstream phenomenon perpetuating the downstream symptom indicators of depression involve neuroinflammatory states due to psychosocial and relational factors such as chronic stress, poor relationships, or substance use. However, any environmental factor that triggers an immune response and inflammation can promote neuroinflammation that manifests as symptoms of mental illness."

The message for teens with depression and their families is that "we are a product of our environment," Loper said. "When our environments are proinflammatory, or cause our immune system to become overactive, then we will develop illness; however, the most potent mediator of inflammation in the brain, and the downstream symptoms of depression, is our relationships with those we love most," he said.

Loper suggested research aimed at identifying other sources of immune-mediated inflammation caused by physical environments and better understanding how environmental phenomenon like ozone may compound previously established risk factors for mental illness could be useful.

The RMD Open study received no outside funding, and its authors had no financial conflicts.

The Developmental Psychology study was supported by the National Institute of Mental Health and the Stanford University Precision Health and Integrated Diagnostics Center. The researchers for that report, and Loper and Barrett had no conflicts to disclose.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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