Does air pollution make Long COVID worse? Researchers weigh up

Researchers discover how particulate matter increases the risk of long COVID, shedding light on the hidden health effects of city living.

Study: Environmental exposures and long COVID in a prospective population-based study in Catalonia (COVICAT study). Image source: miniwide / Shutterstock

In a study recently published in the journal Environmental health perspectivesResearchers assessed the relative risks of Long COVID according to human exposure to different types of environmental pollutants. Their study used data from the Catalan COVICAT cohort (n = 2,853 Catalan adults aged 40-65 years) and found that exposure to air pollutants (particularly particulate matter) increased the risk of long COVID (PM2.5), RR = 1.14 (95% CI: 0.97 – 1.37), PM10 RR = 1.15 (95% CI: 0.98–1.39)) these relationships were not statistically significant. Other environmental pollutants (noise, light and green spaces) showed no such association.

In particular, the study results confirm previous research indicating the role of airborne particulate matter in COVID-19 severity and its indirect association with long-COVID risk through increased initial infection severity, while highlighting subtle differences in long-COVID risk according to gender, age and level of education. It helps inform clinicians and policymakers about priorities in addressing this growing global public health problem.

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 persist over weeks, months, or even years after recovery develop or continue to have an infection with coronavirus disease 2019 (COVID-19). Symptoms vary significantly from patient to patient and may include post-exertional malaise, fatigue, chest or muscle pain, and “brain fog” (cognitive dysfunction).

The duration and severity of Long COVID result in significant debilitation and socioeconomic stress for patients and their families, highlighting the need to identify risk factors and high-risk populations. Previous research has shown that air pollution contributes significantly to the severity of COVID-19 infection and therefore to the risk of long COVID. However, such results have often been limited by short study durations, reliance on self-reported data, and inadequate sample sizes. In addition, the effects of other environmental pollutants remain unknown.

About the study

The aim of the present study is to close existing knowledge gaps by examining the relationships between exposure to urban environmental pollutants and the resulting Long COVID risk. It uses detailed, longitudinal self-reported online questionnaire data from the COVICAT cohort, a long-term prospective population-based cohort of Catalan adults (40–65 years), supplemented by baseline medical data from the GCAT study (2019).

Study data were collected via three online questionnaires conducted during the pandemic (2020, 2021 and 2023). Relevant data included sociodemographic data (gender, age, education level) and clinical data (COVID-19 infection severity, body mass index (BMI), general health status and vaccination details). Participants who did not respond or provided incomplete data were excluded from statistical analyses.

The study also defined and examined the prevalence and risk associations of persistent long COVID symptoms reported in 2021 and persisting into 2023. Exposure to urban environmental pollutants was assessed based on annual averages at participants’ home 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 artificial light at night (ALAN) ).

The association between each individual exposure and participant outcomes was assessed using three robust mixed-effects Poisson regression models adjusted for sociodemographic, clinical, and infection severity factors. Statistical analyzes included as controls participants who reported COVID-19 infections but had no subsequent long-COVID symptoms.

Study results

Of the 2,853 participants included in the final data set, 700 (24.5%) reported long COVID symptoms, of which 153 (5%) reported persistent long COVID symptoms. 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 factor in Long COVID incidence, with participants with a university degree (n=1,557, 22.2%) having a lower prevalence than participants with only primary/lower education (n= 219, 29.2%).

Previous chronic illnesses significantly increased the risk of Long COVID (n = 1,013, 33.3%). Clinical data related to COVID-19 showed that the severity of the infection and the administration of vaccinations before infection were significant influencing factors, with the latter reducing the risk of long COVID.

It is noteworthy that in addition to exposure to suspended particulate matter (PM2.5 RR = 1.14 (95% CI: 0.97-1.37), PM10 RR = 1.15 (95% CI: 0.98-1 ,39)) no association of other urban environmental pollutants was found with the increased prevalence of Long COVID. These results are consistent with previous reports, although in a sample cohort limited to Catalonia. Researchers speculate that particulate matter may indirectly influence Long COVID risk by increasing the severity of the initial infection.

Conclusions

The present study examines the effects of various urban environmental pollutants (air, noise, green spaces and light) on the risk of long COVID or the persistent risk of long COVID. Study results show that suspended particulate matter increases the risk of long COVID disease by worsening the severity of the initial COVID-19 infection. Women, participants with less education, and participants with pre-existing chronic illnesses were found to be at significantly higher risk of long-term COVID-19 infection than their respective counterparts. Surprisingly, other environmental pollutants evaluated were found to have no impact on the incidence or prevalence of long-COVID.

“Further research focusing on Long COVID subtypes, symptom clusters, and possible mechanisms underlying the observed associations will be critical to improving our understanding of this complex disease,” the researchers concluded.