One of the most perplexing aspects of the COVID-19 pandemic was why some people got really ill and ended up needing hospitalization while others only got a mild case of the sniffles. In fact, while more than 6.5 million people died of this disease, some people didn’t even get infected, despite being exposed to the virus on a daily basis.
A lot of research has been devoted to finding reasons for this apparent unpredictability in severity, and many factors have been considered, including age, diet, vitamin deficiency, co-morbidities, living conditions, previous exposure to respiratory viruses, and balance of macrophages in the immune system.
A fascinating new study has now investigated the levels of certain environmental pollutants in the blood of a population of 154 residents of the city of Barcelona. These blood samples were taken back in 2016 for purposes other than studying COVID-19 susceptibility, and were part of the Barcelona Health Survey. Other data were collected from each participant at the time, such as information on chronic disorders (e.g., chronic bronchitis, anemia), mental health, life styles, uses of health services and preventive practices.
The blood samples were analyzed for levels of various organic pollutants (including persistent organic pollutants – POPs) and inorganic minerals, and participants were invited back between late 2020 and mid-2021, to be interviewed again. The researchers were interested in identifying any links between the presence in the blood of 112 different compounds, including 20 rare earth elements, and the frequency of SARS-CoV-2 infection and disease severity experienced by the participants.
The findings, published in the journal Environmental Research, reveal that people with higher blood levels of certain pollutants had a higher risk of becoming infected and of developing the disease. The risk of developing COVID-19 was associated with levels DDD and DDE (derivatives of the pesticide DDT), as well as lead, thallium, ruthenium, tantalum, benzofluoranthene and manganese. High levels of thallium, ruthenium, lead and gold, were associated with a higher risk of infection, while high levels of iron and selenium were protective.
“What our study shows is that individual levels of certain environmental pollutants increase the risk of infection and the risk of developing the disease,” explained Miquel Porta, a physician at IMIM-Hospital de Mar and one of the main authors of the study. Other factors that influence the risk of developing COVID-19 are co-morbidities (i.e., whether the person already suffers from other diseases), smoking, age, education level, density of people in the home, or exposure to the virus on public transport or at work.
Interestingly, of the 112 different chemical substances tested, an average of 32 was detected in each individual participant. Reassuringly, concentrations of several historically prevalent POPs, as well as the minerals arsenic, cadmium, mercury, and zinc, were not associated with COVID-19 symptom severity, nor with SARS-CoV-2 infection. The researchers decided to analyze the impact of the substances when combined in groups of five, since there is scientific evidence that mixtures of pollutants may be more toxic than the individual components on their own.
“An important finding of the study is that it identifies mixtures of up to five substances, from different chemical groups, each of which increases the risk of infection and disease,” said Gemma Moncunill, researcher at ISGlobal and last author of the article.
The authors consider these results to be of “considerable scientific and social relevance,” as they provide the first prospective and population-based evidence of a possible link between individual blood levels of certain pollutants and SARS-CoV-2 infection and COVID-19 severity.
The experts state that their results open numerous research avenues to study the pathways and mechanisms whereby these various substances act on the immune system. These pollutants enter our bodies through multiple routes, from exposure to electronic devices to the feed used in intensive animal farming. Therefore, say the authors, if the associations are confirmed to be causal, policies to control the risks are available.
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