I’m an environmental epidemiologist – that means I look at the health impacts of exposures in the environment such as air pollution, chemicals and environmental noise. I trained as a doctor and worked for six years in hospital before moving into public health and then environmental health – because I wanted to prevent people needing to go into hospital.
There has been a truly impressive amount of research on COVID-19 around the world in the last five months, but there is a long way to go to understand this new disease. The first two epicentres were in areas of China and northern Italy with very bad air quality. Two more recent national studies in the US have found higher mortality from COVID-19 in areas with high air pollution. However, areas with high air pollution are usually areas with high population density where it’s easier for the virus to spread. We need some more research to be certain about links between high air pollution andCOVID-19.
We know that air pollution increases the risk of death from chronic heart and lung conditions – estimates from the Royal College of Physicians suggest that current air pollution contributes to 40,000 deaths per year in the UK. Studies also show that air pollution increases the risk of hospital admission for asthma and COPD and for cardiovascular disease; it is also potentially linked with development of diabetes, dementia and other chronic conditions. Given what we know about air pollution, it would be surprising if there was no impact on COVID-19 as well, but we currently can’t tell how large that impact might be.
A study of mine published in 2019 looking at 300,000 adults in the UK, suggested that UK air pollution causes the equivalent of several months ageing of the lung. Other studies have found that air pollution is linked to exacerbations of asthma and other chronic lung conditions.
Air pollution also increases the risk of heart disease and hypertension. From an individual perspective, the risks from air pollution are a lot smaller than those from lifestyle factors like smoking, being overweight or taking little exercise. The problem is that most people are exposed to air pollution – a relatively small impact on the whole population means that numbers affected add up. Also, while an individual can take actions to lead a healthier lifestyle e.g. quitting smoking, getting air quality improved can be a complex process involving individuals, communities and government.
Some air pollutants such as nitrogen dioxide and ozone are irritants and set up inflammation in the lung. Air pollutants such as fine particulates also set up inflammation in the lung but may additionally penetrate the lung surface and get carried in the blood to other organs. These particles can increase inflammatory responses in the blood and may end up lodged in, for example, blood vessel walls, the brain and the placenta.
There are a small number of studies. These are epidemiological studies investigating associations between air pollution and COVID-19 and exposure studies looking at whether the coronavirus can be carried by particulates in the air. I am not aware of any mechanistic (laboratory) studies investigating if air pollution affects coronavirus infection of lung cells. Most of the studies available are pre-prints, which means they have not yet been through peer-review and published in scientific journals – findings may be modified after peer-review comments and feedback.
We need more epidemiological studies in different countries, published in peer reviewed journals. These need to be supported by evidence from studies on the mechanisms involved. Finally, all evidence needs to be reviewed, ideally by national or international panels involving air pollution experts, to agree on the likely size of the impact and the most important mechanisms. This can then be used to inform public health actions.
Areas with poorer air quality also tend to be more deprived areas, with higher population density and increased rates of chronic disease and obesity. In countries like the UK, these also tend to be areas with higher prevalence of people from non-white ethnic origins. Factors such as high population density increase the risk of transmission of the COVID-19, while factors such as ethnic origin, obesity and pre-existing disease can increase the risk of severe disease.
The two national US studies by Wu et al and Liang et al are very thorough studies, with rigorous methodologies, conducted by leading air pollution research groups. However, they compare areas (US counties) not individuals and this means there is always some uncertainty about whether the difference between areas is related to factors other than air pollution – even though the statistical analyses have some adjustments for these factors. We will need individual-level follow-up studies to confirm the findings.
The World Health Organization estimates that air pollution kills 4 million people per year globally. In our own country the figure is 40,000. But progress on reducing air pollution levels is very slow. COVID-19 is leading to a complete reassessment of our priorities as individuals and as a society. Information about a link with air pollution could help change the way in which we view air pollution, so it’s seen as an unacceptable avoidable risk.
I think there will be a lot of changes to working patterns, with more people working from home. I hope that the falls in air pollution we’ve seen will be maintained. Also, I think a lot of people have become aware of the importance of good health and a healthy lifestyle including regular exercise. I hope that’s a permanent change.
Read the full study by Wu et al
Read the full study by Liang et al
Listen to Professor Hansell’s podcast about air pollution and COVID-19 at the Guardian