Exposure to the 1952 Great Smog increased the likelihood of being diagnosed with asthma

We currently understand very little about the long term consequences of pollution and particulate matter in our air. We have evidence that air pollution can worsen asthma symptoms and rates of heart attacks spike during times of high pollution. We also know that exposure of cells in culture to environmental pollutants causes cell damage and an increase in inflammation but don’t yet know if this can lead to the development of asthma or other lung diseases long term. In 1952, London was covered in a thick layer of smog for 5 days in an event that came to be known as the Great Smog of 1952. During this time, air pollution levels were between 5 and 23 times the currently accepted regulations. Much research has been focused on this event as it presents a ‘natural experiment’ where groups of individuals were all exposed to an experimental condition that we can look back on an test hypotheses against. Research to date has identified several short term complications of this great smog including increased mortality, heart attacks, and lung infections. Recently, a research paper by Bharadwaj and colleagues out of the US has shed some light onto the long term consequences of being exposed to this Great Smog and in the process has linked air pollution to the likelihood of developing asthma.

The researchers collected information from 2,916 respondents in the English Longitudinal Study on Aging born between 1945 and 1955. They tabulated the incidence rate of asthma in this population and separated them out depending on their age at the time of the Great Smog and whether they lived in London or another area in England. Included in this sample were 199 people who were born after the Great Smog and so were not exposed to it. The team saw that exposure to the Great Smog in the first year of life (ie. Born in 1952) increased your likelihood of having asthma in childhood by 19.8%. Additionally, exposure to the Great Smog in utero (in the womb) increased your risk of childhood asthma by 7.9%. Finally, they saw that early life exposure increased your risk of having asthma as an adult by 9.5%. The reason for this increase incidence is likely due to changes in the development of the young child’s lungs as a result of the pollution.

This study is powerful because it was able to compared a large group of people exposed to a high level of pollution and compare them to people living in different urban areas in the same year. This greatly limits several confounders that normally plague epidemiologic research like differences in wealth, education, and urban vs. rural living. We still don’t yet know the exact mechanism at play here but by looking at other ‘nature experiment’ like the 2013 Eastern China Smog we may be able to unravel how pollution affects lung development, lung disease, and hopefully implement policy changes to reduce pollution levels worldwide.

Image Credit: N T Stobbs

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