Exposure to Air Pollution Linked to Risk of Long COVID in Young Adults

Long-term exposure to ambient air pollution was associated with an increased risk of long COVID among young adults, according to a Swedish population-based cohort study.

For each increase in interquartile range (IQR) in exposure to particulate matter ≤2.5 μm (PM_2.5) in 2019 (median annual exposure 6.39 μg/m³), the odds of developing long COVID increased by about 30%, reported Erik Melén, MD, PhD, of the Karolinska Institutet in Stockholm, and co-authors.

The adjusted odds ratio of PM_2.5 per IQR increase was 1.28 (95% CI 1.02-1.60) for long COVID, while the odds ratios were 1.65 (95% CI 1.09-2.50) for dyspnea symptoms and 1.29 (95% CI 0.97-1.70) for altered smell/taste, Melén and team noted in Lancet Regional Health – Europe.

Associations tended to be stronger for participants with asthma, and those who had COVID in 2020 compared with 2021, they added.

“Ambient air pollution exposure have been shown to be positively associated with increased levels of inflammatory cytokines and proteins, which have been proposed as possible causes of multiple symptoms of post COVID-19 conditions,” Melén and team wrote. “In addition, air pollution has been found to be associated with immune dysregulation including immune suppression, which was reported to be associated with risk of persistent symptoms after COVID-19.”

“The virulence of the SARS-CoV-2 virus may be altered in polluted regions as a contributing mechanism,” they continued. “Furthermore, long-term air pollution exposure can have adverse effects on a wide range of comorbidities such as cardiometabolic diseases and respiratory diseases, which have been found to be associated with risk of developing long COVID. This is consistent with our results that the observed association tended to be stronger among participants with asthma.”

The authors noted that PM_2.5 exposure is often the result of road pollution, shipping pollution, industrial processes, or some forms of residential heating systems.

Other forms of air pollution were analyzed in the study, including particulate matter ≤10 μm (PM₁₀), nitrogen oxides (NO_x), and black carbon (BC), but none of these were significantly linked to risk of long COVID.

“Little is known about the importance of the timing of air pollution exposure, for example, early-life exposure when the lungs are thought to be more susceptible to environmental exposure, or exposure later in life,” Melén and colleagues noted.

“Since ambient air pollution is a modifiable risk factor through national or regional public health regulations as well as individual interventions, our results support the broad public health benefits of continuous efforts to reduce ambient air pollution levels,” they concluded.

Melén and team used data from the BAMSE (the Swedish abbreviation for Children, Allergy, Milieu, Stockholm, Epidemiology) cohort. Participants answered a web-questionnaire on persistent symptoms following acute SARS-CoV-2 infection from October 2021 to February 2022.

Median age was 26.5, and 60.7% were female. About 52% of participants reported being bed-bound after infection, while only 3.5% had been vaccinated before their infection.

The study defined “long COVID” as symptoms after confirmed COVID lasting 2 months or longer. The most common symptoms included changes in taste and/or smell (10.6% of patients), dyspnea (4.8%), and fatigue (4.5%).

Ambient air pollution levels at individual-level addresses were estimated using dispersion modeling.

The authors acknowledged several limitations to the study, including its observational nature, potential errors in the reporting of self-diagnosis of COVID, misclassification in the level of air pollution exposure, variation in patient vaccination status, and the inability to eliminate all confounding factors.