Does air pollution worsen Long COVID? Researchers weigh in

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Dec 5 2024

Researchers uncover how particulate matter amplifies Long COVID risk, shedding light on the hidden health effects of urban living.

Study: Environmental Exposures and Long COVID in a Prospective Population-Based Study in Catalonia (COVICAT Study). Image Credit: miniwide / Shutterstock

In a recent study published in the journal Environmental Health Perspectives, researchers evaluated the relative risks of Long COVID following human exposure to several types of environmental pollutants. Their study leveraged data from the Catalonian COVICAT cohort (n = 2,853 Catalonian adults aged 40–65) and found that while air pollutant exposure (particularly particulate matter) increased Long COVID risk (PM2.5 RR = 1.14 [95% CI: 0.97–1.37], PM10 RR = 1.15 [95% CI: 0.98–1.39]), these associations were not statistically significant. Other environmental pollutants (noise, light, and green spaces) showed no such association.

Notably, study findings validate previous research suggesting the role of suspended particulate matter in COVID-19 severity and its indirect link to Long COVID risk through heightened initial infection severity, while highlighting subtle differences in Long COVID risk across sex, age, and education levels. It helps inform clinicians and policymakers of priorities when tackling this growing global public health concern.

Background

Long COVID, also called ‘post-COVID-19 syndrome’ and ‘post-acute sequelae of COVID-19 (PASC)’ is an umbrella term for a group of symptoms that develop or persist for weeks, months, or even years following recovery from a coronavirus disease of 2019 (COVID-19) infection. Its symptoms vary substantially between patients and may include post-exertional malaise, fatigue, chest or muscle pain, and ‘brain fog’ (cognitive dysfunctions).

The duration and severity of Long COVID impart significant debilitation and socioeconomic stress to patients and their families, highlighting the need for identifying its risk factors and high-risk populations. Previous research has suggested that air pollution significantly contributes to COVID-19 infection severity and, in turn, Long COVID risk. However, such findings have often been limited by short study durations, reliance on self-reported data, and insufficient sample sizes. Furthermore, the impacts of other environmental pollutants remain unknown.

About the Study

The present study aims to address present knowledge gaps by investigating the associations between urban environmental pollutant exposure and subsequent Long COVID risk. It leverages detailed, longitudinal self-reported online questionnaire data from the COVICAT cohort, a long-term prospective population-based cohort of Catalonian adults (40-65 years), supplemented with baseline medical data from the GCAT study (2019).

Study data was collected via three online questionnaires administered during the pandemic (2020, 2021, and 2023). Relevant data included sociodemographics (sex, age, education level) and clinical data (COVID-19 infection severity, body mass index [BMI], general health status, and vaccination details). Participants who remained unresponsive or provided incomplete data were excluded from statistical analyses.

The study further defined and investigated the prevalence and risk associations of ‘persistent Long COVID,’ symptoms which were reported in 2021 and persisted through 2023. Urban environmental pollutant exposure was assessed based on annual averages at participants' residential addresses. These included air (suspended particulate matter [PM2.5, PM10], nitrogen dioxide [NO2], and ozone [O3]), green space availability (including normalized difference vegetation index [NDVI]), nighttime road-traffic noise, and outdoor melanopic illuminance (blue light artificial light at night [ALAN]).

The association between each individual exposure and participant outcomes was evaluated using three mixed-effect robust Poisson regression models adjusted for sociodemographic, clinical, and infection severity factors. Statistical analyses included participants reporting COVID-19 infections but no subsequent Long COVID symptoms as controls.

Study Findings

Out of the 2,853 participants included in the final dataset, 700 (24.5%) reported Long COVID symptoms, of which 153 (5%) reported persistent Long COVID. Women (n = 1,788, 27.6%) reported higher Long COVID prevalence than their male counterparts (n = 1,065, 19.4%). Education was found to be a significant determinant of Long COVID incidence, with university-educated participants (n = 1,557, 22.2%) demonstrating lower prevalence than those with only primary/lower education (n = 219, 29.2%).

Prior chronic disease substantially increased Long COVID risk (n = 1,013, 33.3%). COVID-19-associated clinical data revealed that infection severity and pre-infection vaccination administration were significant determinants, with the latter reducing Long COVID risk.

Notably, apart from suspended particulate matter exposure (PM2.5 RR = 1.14 [95% CI: 0.97–1.37], PM10 RR = 1.15 [95% CI: 0.98–1.39]), no other urban environmental pollutants were found to be associated with the heightened prevalence of Long COVID. These findings align with previous reports, albeit in a Catalonian-restricted sample cohort. Researchers speculate that particulate matter may influence Long COVID risk indirectly by increasing the severity of the initial infection.

Conclusions

The present study investigates the impacts of several urban environmental pollutants (air, noise, green spaces, and light) on Long COVID or persistent Long COVID risk. Study findings reveal that suspended particulate matter increased the risk of Long COVID by exacerbating the severity of the initial COVID-19 infection. Women, participants with limited education, and those with pre-existing chronic diseases were found to demonstrate substantially higher Long COVID risk than their respective counterparts. Surprisingly, other evaluated environmental pollutants were not found to impact Long COVID incidence or prevalence.

“Further research focusing on Long COVID subtypes, symptom clusters, and potential mechanisms underlying observed associations will be crucial for enhancing our understanding of this complex condition,” the researchers concluded.