People exposed to air pollution experienced Covid-19 as if they were 10 years older, according to research. It found people recently exposed to dirtier air before contracting the illness spent four days longer in hospital, the same impact as on those 10 years their senior.

The Belgian study also showed that air pollution levels measured in patients’ blood were linked to a 36% increase in the risk of needing intensive care treatment. A separate study in Denmark showed air pollution exposure was linked to a 23% increase in the risk of death from Covid-19. In both studies, the level of air pollution was below legal EU standards.

Previous research suggested that air pollution worsened Covid outcomes but, rather than assessing groups of people together, the new studies followed individual patients and therefore give much more confidence in the results.

Air pollution is known to be a major risk factor in aggravating respiratory diseases. It increases inflammation in the lungs and weakens immune defences, and causes pre-existing lung problems that worsen the outcomes of new infections.

The new research shows cutting air pollution is a crucial measure for reducing illness and deaths during future outbreaks of respiratory diseases, including the annual flu season. Cleaner air brought health benefits almost as great as some of the medical treatments given to the Covid-19 patients, the research showed.

“Reducing air pollution, even when at relatively low levels, increases the health of the population and makes them less susceptible to future pandemics,” said Prof Tim Nawrot, at Hasselt University in Belgium. “The pandemic placed an enormous strain on doctors, nurses and other healthcare workers. Our research suggests that air pollution made that burden even greater.”

Dr Zorana Jovanovic Andersen, at the University of Copenhagen, Denmark, and senior author of the Danish study, said: “These results show how air pollution can compromise our immune system and leave us vulnerable. Reduction of air pollution should be at the heart of preventive measures for current and future pandemics, as well as a strategy for dealing with seasonal influenza pandemics.”

Many previous studies assessing the link between Covid and air pollution were what epidemiologists call “ecological studies”, which assess the relationship using averaged data for a whole population. These could be completed quickly and some factors that may influence the link could be taken into account. But hidden factors could not be ruled out and the variation of air pollution over short distances could not be accounted for. In contrast, the new studies followed the illness and air pollution exposure in individual people.

The Belgian study, published in the European Respiratory Journal (ERJ), followed more than 300 patients who were hospitalised with Covid-19 between May 2020 and March 2021. Data on the levels of three pollutants – fine particles, nitrogen dioxide and soot – at the patients’ homes were gathered and the amount of soot in the patients’ blood was also measured. Other factors known to affect Covid-19 disease, such as age, sex and weight, were taken into account.

The difference in air pollution used in the studies to assess the impact on Covid-19 was based on the range of pollution levels recorded. The higher level used was midway towards the top of the range – at the 75% mark – and the lower level was towards the bottom of the range – at the 25% mark.

The researchers found people exposed to the higher level a week before hospital admission went on to spend about four more days in hospital. They also found the lower level of air pollution resulted in health improvements equivalent to 40-80% of the benefits of medicines used to treat Covid, such as remdesivir.

The Danish study, also published in the ERJ, used Denmark’s national Covid-19 surveillance system to follow all 3.7 million people in the country aged 30 or older over the first 14 months of the pandemic. It found patients exposed to the higher level of small particle air pollution in 2019 were about 23% more likely to go on to die from Covid-19. A similar recent study in New York City found the increased risk of death was 11%.

Prof Charlotte Suppli Ulrik, head of the European Respiratory Society assembly on the environment and epidemiology, said: “We are finding more and more evidence that breathing polluted air is contributing to lung diseases, including infections. Although the Covid-19 global health emergency is over, the impact of pollution on our health is continuing and we need governments to take action for the sake of our health and our health services.”

Prof Jordi Sunyer and Dr Payam Dadvand, at the Barcelona Institute for Global Health and commenting on the Belgian study, said it showed that cutting air pollution would be “a very effective way to protect our population” from Covid-19 and other respiratory infections.

“Despite the evidence, the air quality standards are still above harmful values and even these rather lax standards are still not met in most cities in the world, including many European cities,” they said.

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