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  • Researchers investigated the link between long-term exposure to nitrogen dioxide (NO2) and the need for ICU care and mechanical ventilation for COVID-19.
  • They found that exposure to higher levels of NO2 correlates to a higher need for ICU care and mechanical ventilation.
  • The researchers caution that their study only found a correlation—not causation—and that further research is needed to understand their findings better.

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Nitrogen dioxide (NO2) is a traffic-related pollutant gas released when burning fossil fuels.

Long-term exposure to NO2 causes many health problems and is linked to a higher risk of all-cause, cardiovascular and respiratory-related death.

A study conducted with healthcare data from 4,443 fatal cases of COVID-19 in 2020 found that long-term exposure to high levels of nitrogen dioxide correlates to increased mortality risk from COVID-19.

Knowing how long-term nitrogen dioxide exposure affects COVID-19 outcomes could help policymakers better allocate resources to treat the condition.

Recently, researchers investigated the effects of long-term NO2 exposure and the need for ICU and mechanical ventilation treatment for COVID-19.

They found that long-term NO2 exposure was linked to an increased need for ICU care and mechanical ventilation.

Researchers presented the findings at the Euroanaesthesia Congress in Milan, Italy.

The researchers gathered air pollution data from 2010 to 2019 for 392 of Germany’s 402 counties for the study. They used this data to calculate long-term annual mean levels of NO2, ranging from 4.6 µg/m³ to 32 µg/m³. The lowest levels were in Suhl and the highest in Frankfurt.

They also gathered data on the number of occupied ICU beds and the need for mechanical ventilation from the German Interdisciplinary Association for Intensive Care and Emergency Medicine registry from April 16, 2020, to May 16, 2020, when government officials lifted lockdown restrictions.

Next, they analyzed the data and adjusted their findings for demographic factors such as population density, age and sex distribution, socioeconomic factors, and health parameters such as pre-existing health conditions affecting COVID severity.

Altogether, they noted that there were 169,840 cases of COVID-19 in Germany until May 16, 2020, and 8,433 COVID-related deaths.

Their data analysis found that an increase of 1 μg/m3 NO2 was linked to a 3.2% higher need for ICU care and a 3.5% higher need for mechanical ventilation.

When asked what might explain the study’s findings, Dr. Tia Babu, Acting Assistant professor in the Divison of Allergy and Infectious Diseases at the University of Washington, not involved in the study, told Medical News Today:

“Nitrogen dioxide exposure is associated with a myriad of effects to the lungs, including lung injury, decreased lung function, and inflammation,” Dr. Babu said. “Perhaps the chronic exposure to nitrogen dioxide leads to decreased pulmonary function or an abnormal local lung immune response to the SARS-CoV-2 virus.”

MNT also spoke with Dr. Fady Youssef, a board certified pulmonologist, internist, and critical care specialist at MemorialCare Long Beach Medical Center in Long Beach, California. Dr. Youssef was not involved in the study.

He said pollutants can promote a proinflammatory state in the lungs that can have an additive effect on inflammation triggered by COVID-19.

Dr. Susanne Koch, a professor at the Department of Anaesthesiology & Intensive Care, Charité – Universitätsmedizin Berlin, Germany, lead author of the study, explained this additive effect to MNT:

“[A protein called] ACE-2 helps “put the brakes” on inflammation, but exposure to air pollutants triggers inflammation or ‘releases the brakes.’ And again, when the SARS-CoV-2 virus binds to ACE-2, these brakes are removed, which leads to an additive effect, more severe inflammation and a more severe course in COVID-19.”

The researchers concluded that individual risk for COVID-19 morbidity is influenced by long-term exposure to NO2.

When asked about the study’s limitations, Dr. Koch told MNT that due to the cross-sectional, epidemiological design of the study, their research does not guarantee causal relations. She also noted that as many risk factors for COVID-19 may be triggered by air pollution, their models may underestimate its impact on health.

Dr. Youssef added: “There are many other variables that can be associated with environments where NO2 levels are elevated that could be responsible for the correlation, [although] the study did control for some of them.”

Babu noted that examples of these other variables, including differences in medical practices in urban areas such as increased ICU care capacity, may have contributed to the study’s observations.

Liuhua Shi, ScD, Assistant Professor at Gangarosa Department of Environmental Health at Emory University, further explained that NO2 might also serve as a proxy for unexamined traffic-related air pollutants such as soot, trace metals, and ultrafine particles.

Dr. Shi added that the study did not assess real-time exposures and that country-level features may not represent the features of individual COVID-19 patients, meaning that their adjustment for socioeconomic, health and demographic factors may be inadequate.

When asked about what this study means for the environment, Koch explained:

“While the COVID-19 pandemic may end by reaching herd immunity through infection or vaccination, exposure to ambient air pollution will continue to affect people’s health. The only remedy is reducing emissions.”

“The transition to renewable energy, clean transportation, and sustainable agriculture is urgently needed to improve air quality, which will also help mitigate climate change, to improve population health and quality of life around the world,” she concluded.