Public Release: 

Exposure to air pollution 30 years ago associated with increased risk of death

Exposure to air pollution more than 30 years ago may still affect an individual's mortality risk today, according to new research from Imperial College London

Imperial College London

The new report comes from one of the world's longest running air pollution studies, which included 368,000 people in England and Wales followed over a 38 year period. The team, from the MRC-PHE Centre for Environment and Health, estimated air pollution levels in the areas where the individuals lived in 1971, 1981, 1991 and 2001, using measurements from Britain's extensive historic air pollution monitoring networks.

Highest risks were seen for respiratory disease, such as bronchitis, emphysema and for pneumonia. Air pollution also affected mortality risk from cardiovascular diseases, such as heart disease.

Dr Anna Hansell, lead author of the study, from the MRC-PHE Centre for Environment and Health at Imperial, said: "Air pollution has well established impacts on health, especially on heart and lung disease. The novel aspects of our study are the very long follow-up time and the very detailed assessment of air pollution exposure, using air quality measurements going back to the 1970s.

"Our study found more recent exposures were more important for mortality risk than historic exposures, but we need to do more work on how air pollution affects health over a person's entire lifetime.

"We were surprised to find pollution has effects on mortality that persist over three decades after exposure."

In the study, published in the journal Thorax, the researchers assessed levels of black smoke and sulphur dioxide air pollution from 1971 to 1991 and PM10 air pollution in 2001. Both black smoke and PM10 are measures of small particles in the air. Black smoke and sulphur dioxide were produced mainly by burning fossil fuels (including coal, oil, diesel, petrol).

Today, the methods of measuring air pollution have changed. A common measure is PM10, which measures very small particles that are less than 10 microns in size. These can travel deep into the lungs and may even be small enough to enter the bloodstream. This type of air pollution is mainly produced by transport and industry with a contribution from construction activities and natural sources (e.g. sea salt, soil).

In the study, risks from pollution exposures were reported in units of 10 micrograms per cubic metre of air. Researchers compared these levels of exposure with data on disease and deaths. The study suggests that for every additional unit of pollution that people were exposed to in 1971, the risk of mortality in 2002 to 2009 increases by two per cent.

The researchers also looked at more recent exposure and found a 24 per cent increase in mortality risk in 2002 to 2009 for each additional unit of pollution people were exposed to in 2001.

Dr Rebecca Ghosh, co-author of the study from the School of Public Health at Imperial, said "Putting this in context, an individual who lived in a higher polluted area in 1971 had a 14 per cent higher risk of dying in 2002 to 2009 than someone who had lived in a lower polluted area. An individual living in a higher polluted area in 2001 also had an increased risk of mortality of 14 per cent compared to someone in a low pollution area.

"However, although there are similar sizes of risk from exposure in 1971 and 2001, there are much lower exposure levels. For instance, comparing highest and lowest polluted areas in 1971, there was a 52 micrograms difference in black smoke per cubic metre of air, but in 2001 the comparable difference was 6 micrograms per cubic metre of air of PM10.

Dr John Gulliver, co-author and Senior Lecturer at the MRC-PHE Centre for Environment and Health at Imperial, said: "Levels of all types of air pollution in the UK have reduced dramatically since the start of our study period, with levels of black smoke currently estimated to be about 20 per cent of what they were in the 1970s."

Dr Anna Hansell added: "It's important to remember that the effects of air pollution are small compared to other risk factors. Your risk of dying early is much more dependent on other aspects of your lifestyle, like whether you smoke, how much you exercise, whether you are overweight, as well as on medical factors like your blood pressure. This was true even with the higher air pollution levels in the 1970s.

"However, our study adds to the weight of evidence that suggests breathing in air pollution isn't good for us in either the short or long-term. We need to continue collective efforts to reduce air pollution levels, both in the UK and internationally."

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For more information:

Kate Wighton
Research Media Officer - Medicine
Imperial College London
email: k.wighton@imperial.ac.uk
Tel: 44-0-20-7594 2410

Notes to editors

1. "Historic air pollution exposure and long-term mortality risks in England and Wales: prospective longitudinal cohort study" by Anna Hansell, Rebecca E Ghosh, Marta Blangiardo, Chloe Perkins, Danielle Vienneau, Kayoung Goffe, David Briggs, John Gulliver is published in Thorax doi:10.1136/thoraxjnl-2015-207111.

2. The figures related to mortality risk come from the paper, Table 3: a two per cent increase risk in mortality in 2002 to 2009 per 10 μg/m3 black smoke in 1971 and from Table 4: a 24 per cent increase in mortality risk 2002 to 2009 per 10 μg/m3 PM10 exposure related to exposures in 2001. These figures on risks are statistically significant and are adjusted for age, sex, individual and area social-economic status, region and population density. These mortality risk estimates have been used to calculate the 14 per cent differences in risk between areas with highest pollution (90th centile) and lowest pollution (10th centile) levels that are in the quote from Dr Hansell.

3.In this study, the researchers were unable to calculate how many deaths today might be attributable to historic exposure to air pollution -- this requires further dedicated research.

4. The researchers mainly looked at particle air pollution in this study, which is thought to be one of the most dangerous components of air pollution. They did not look at nitrogen oxide, another major component of air pollution, as the necessary measurements for this were not available before the 1990s.

5. About the MRC-PHE Centre for Environment and Health

The MRC-PHE Centre for Environment and Health undertakes world-leading research in the fields of environment and health, in order to inform health policy and the understanding of key issues affecting society. It was formed in June 2009 as a partnership between Imperial College and King's College London, and is funded by the Medical Research Council (MRC) and Public Health England (PHE). The Director is Professor Paul Elliott (Imperial) and the Deputy Director is Professor Frank Kelly (King's). The Centre incorporates the UK Small Area Health Statistics Unit (SAHSU) at Imperial College, and the Environmental Research Group (ERG) at King's College London, in addition to bringing together leading researchers from the National Heart and Lung Institute at Imperial College, other departments of the Faculty of Medicine at Imperial College, and researchers at King's College, St George's University of London and London School of Hygiene and Tropical Medicine.

6. About Imperial College London

Imperial College London is one of the world's leading universities. The College's 14,000 students and 7,500 staff are expanding the frontiers of knowledge in science, medicine, engineering and business, and translating their discoveries into benefits for society. Founded in 1907, Imperial builds on a distinguished past -- having pioneered penicillin, holography and fibre optics -- to shape the future. Imperial researchers work across disciplines to improve health and wellbeing, understand the natural world, engineer novel solutions and lead the data revolution. This blend of academic excellence and its real-world application feeds into Imperial's exceptional learning environment, where students participate in research to push the limits of their degrees.

Imperial collaborates widely to achieve greater impact. It works with the NHS to improve healthcare in west London, is a leading partner in research and education within the European Union, and is the UK's number one research collaborator with China. Imperial has nine London campuses, including its White City Campus: a 25 acre research and innovation centre in west London. At White City, researchers, businesses and higher education partners are co-locating to create value from ideas on a global scale. http://www.imperial.ac.uk

7. Funders

The work of the UK Small Area Health Statistics Unit is funded by Public Health England as part of the MRC-PHE Centre for Environment and Health, funded also by the UK Medical Research Council. The study also received support from a Wellcome Trust Intermediate Clinical Fellowship study on Chronic Health Effects on Smoke and Sulphur (CHESS), grant number 075883.

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