Certain air pollution gases elevate COPD risk for adults: US study
Findings suggest exposure to benzene, toluene may aid disease development
Exposure to certain air pollution gases — pollutants called volatile organic compounds (VOCs), especially benzene and toluene — significantly increases the risk of chronic obstructive pulmonary disease (COPD) among adults in the U.S., according to a new study.
Indeed, one statistical model found COPD risk was three times higher for individuals with the highest levels of benzene — a chemical used in industrial processes — in one group compared with those in the group with the lowest levels.
“The findings provide compelling evidence that exposure to environmental VOC pollutants … may contribute significantly to COPD development in the general population,” the researchers wrote.
The results “may also inform environmental health policies aimed at better controlling VOC emissions and protecting susceptible populations from COPD,” the researchers added.
Titled “Association of volatile organic compound levels with chronic obstructive pulmonary diseases in NHANES 2013-2016,” the study was published in Nature Scientific Reports.
Air pollution gases linked to COPD found both indoors and outside
Exposure to air pollution is recognized as a significant risk factor for COPD, an inflammatory disease of the lungs characterized by blocked airways, persistent cough with mucus, wheezing, and shortness of breath.
An important part of air pollution, VOCs are emitted as gases into the air, at room temperature, from products or processes. Indoor sources include paint and paint thinners, adhesives, cleaners, and disinfectants. Gasoline, wood burning, oil and gas extraction/processing, and industrial emissions comprise outdoor VOC sources.
While previous research has linked exposure to certain VOCs, including benzene and toluene, with COPD exacerbations, or a sudden worsening of symptoms, these studies focused mainly on individual pollutants and their impact on health.
“Given that the general population is usually exposed to multiple VOCs simultaneously, it is crucial to understand the cumulative health effects of VOCs mixtures,” the researchers wrote.
Now, a team of scientists in China sought to determine whether blood VOC levels were associated with COPD risk. To that end, they analyzed 2013-2016 data from the National Health and Nutrition Examination Survey (NHANES), a U.S. database that collects information on people’s health and diet.
The final analysis included data from 2,411 males and 2,572 females: 1,352 were categorized as having COPD, and 2,721 were in the non-COPD group.
VOCs with levels above the detection limit in the NHANES database were examined. These were benzene, chloroform, toluene, tetrachloroethene, 1,4-dichlorobenzene, o-xylene, m-p-xylene, and bromodichloromethane.
The COPD patients were more likely to be younger than 65 and non-Hispanic white individuals compared with those without the disease. Those in the COPD group also were more likely than their counterparts to have at least a high school education, and to be former drinkers. The researchers noted that significantly higher levels of benzene and toluene were detected in the blood of COPD patients relative to those in the non-COPD group.
Benzene levels in blood linked to higher risk of COPD in models
All participants’ VOC blood levels were divided into four groups, or quartiles (Q1-4), from lowest to highest.
Using a statistical model that adjusted for sex, age, and ethnicity, COPD risk was found to be about three times greater among those with the highest levels of benzene (Q4) compared with those with the lowest levels (Q1). The highest levels of 1,4-dichlorobenzene were linked to a 1.76 times greater risk, while the highest levels of m-p-xylene or toluene were associated with a twofold increased risk.
A second model added an adjustment for educational level, drinking status, body mass index, or BMI, which is a ratio of height and weight, and poverty income ratio — a measure of income relative to the federal poverty line.
Here, the group with the highest benzene levels had a 2.7 times higher risk of COPD than those in Q1. The COPD risk was increased by more than 1.5 times among those with the highest levels of 1,4-dichlorobenzene, toluene, or m-p-xylene, and by more than twofold among those with the highest o-xylene levels.
Blood levels of toluene and m-xylene were found to have significant non-linear relationships with COPD risk, meaning increasing levels of these air pollution gases in blood did not parallel increasing COPD risk.
“These complex dose-response patterns warrant future investigations to elucidate the underlying biological mechanisms,” the researchers wrote.
Study highlights need to examine mixtures of air pollution gases
Further statistical analyses showed that different VOCs had varying effects on COPD risk, with benzene and o-xylene having the greatest impact.
“This highlights the importance of examining mixtures of VOCs, rather than individual chemicals in isolation, when assessing the impact of VOCs exposure on respiratory health,” the team wrote.
The team then used six machine learning models to predict COPD risk based on VOC levels. Machine learning is a form of artificial intelligence that uses algorithms to analyze data, learn from its analyses, and then make a prediction about something.
A specific model, called XGBoost, was the best at predicting COPD occurrence, with an accuracy of 97.09% and a precision of 100%.
Lastly, the team found that an average increase of 1 nanogram per milliliter of blood of benzene was associated with an 88% higher COPD frequency. A similar blood level increase of o-xylene was linked to a 51% higher frequency, and of m-p-xylene to a 58% higher occurrence.
These data suggest that environmental VOCs exposure may be a novel risk factor involved in COPD [development]. … Further research is warranted to confirm our findings and explore the underlying mechanisms.
“This population-based study provides … evidence that exposure to VOCs, especially benzene and toluene, is significantly associated with increased prevalence of COPD among US adults,” the researchers wrote.
“The relationships are nonlinear and VOC mixtures may jointly contribute to COPD risks,” the team added.
According to the researchers, “these data suggest that environmental VOCs exposure may be a novel risk factor involved in COPD [development]. Further research is warranted to confirm our findings and explore the underlying mechanisms.”
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