Air Pollution Exposure May Be Linked to Higher Asthma Risk

TOPLINE:

Long-term exposure to ambient air pollutants over 48 months was associated with an increased risk for asthma exacerbation in women, even at low concentrations. Nitrogen dioxide (NO₂) showed the strongest association with higher odds of exacerbation. A plant-based diet did not modify these effects.

METHODOLOGY:

• Researchers assessed the associations between 48-month air pollution exposure and asthma exacerbations in the Nurses’ Health Study II cohort and examined whether a plant-based diet modifies these relationships.
• Overall, they analyzed 4326 women (mean age, 43 years; 96.7% White individuals) with physician-diagnosed asthma and medication use during 1997-1998 and 2013-2014 periods.
• Plant-based diet adherence was evaluated every 4 years using a validated food-frequency questionnaire that categorized intake into 18 groups (12 plant-based and six animal-based) and generated a Plant-Based Diet Index score ranging from 18 to 90.
• Residential exposures to fine particulate matter (PM_2.5), NO₂, and ozone (O₃) were measured over 48-month periods before outcome assessments.
• The main outcome was asthma exacerbation, defined as hospital admission, emergency department visits, or urgent care visits due to uncontrolled asthma in the past year, assessed in 1998 and 2014.

TAKEAWAY:

• Median 48-month concentrations of PM_2.5 decreased from 13.7 μg/m³ in 1993-1997 to 8.9 μg/m³ in 2009-2013, and those of NO₂ dropped from 12.0 ppb to 6.6 ppb. However, median 48-month concentrations of ozone increased from 25.5 ppb to 27.8 ppb.
• In adjusted single-pollutant models, higher exposures to PM_2.5 and NO₂ were associated with increased odds of asthma exacerbation (adjusted odds ratio [aOR], 1.43; 95% CI, 1.14-1.80 and aOR, 1.25; 95% CI, 1.12-1.38, respectively).
• However, in adjusted multipollutant models, higher NO₂ exposure remained significantly associated with an increased risk for asthma exacerbation (aOR, 1.23; 95% CI, 1.06-1.42), whereas higher exposures to PM_2.5 and O₃ were not.
• No significant interaction was observed between air pollutants and plant-based diet index scores in relation to asthma exacerbation risk (P = .69 for PM_2.5; P = .29 for NO₂; P = .60 for O₃).

IN PRACTICE:

“Our results add to growing evidence that supports lowering acceptable standards for key air pollutants and highlights the need to identify personal, modifiable strategies of increasing resilience among susceptible populations, including women with asthma,” the authors wrote.

SOURCE:

The study was led by Jing Gennie Wang, MD, Division of Pulmonary Critical Care and Sleep Medicine at The Ohio State University Wexner Medical Center in Columbus, Ohio. It was published online on July 28, 2025, in Annals of the American Thoracic Society.

LIMITATIONS:

The study population consisted predominantly of White female nurses, limiting generalizability. The Plant-Based Diet Index score could not distinguish between whole-food and ultraprocessed plant-based diets, potentially affecting the assessment of diet-pollution interactions. Residential mobility among participants may have introduced some exposure misclassification.

DISCLOSURES:

The study received funding from the Nurses’ Health Study II cohort infrastructure grant and the American Lung Association Early Career Investigator Award. Most authors declared receiving grants from the American Lung Association, and two authors reported receiving financial support from some pharmaceutical organizations.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.