Exposure to air pollution more than 30 years ago may still affect an individual’s risk of dying prematurely today, according to new research from Imperial College London.
Published online today (February 9) in the journal Thorax, the report derives comes from one of the world’s longest running air pollution studies, which followed 368,000 people in England and Wales over a 38-year period.
The team, from the MRC-PHE Centre for Environment and Health at Imperial College London, estimated air pollution levels in the areas where the individuals lived in 1971, 1981, 1991 and 2001, using measurements from the UK’s “extensive historic air pollution monitoring networks”.
And, according to the study, the highest risks from air pollution were for respiratory diseases such as bronchitis, emphysema and pneumonia. Air pollution also affected mortality risk from cardiovascular diseases, such as heart disease.
Lead author of the study, Dr Anna Hansell, 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.”
Researchers assessed levels of black smoke and sulphur dioxide air pollution from 1971 to 1991 – mainly produced by burning fossil fuels such as coal, oil, diesel and petrol – as well as particulate matter PM10 air pollution in 2001.
Today, however, methods of measuring air pollution have changed, as PM10 is a common measure of small particles 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 2%.
The researchers also looked at more recent exposure and found a 24% 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% 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% 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 six micrograms per cubic metre of air of PM10.”
The research team said that all types of air pollution had generally improved a great deal since the start of their study period in the 1970s, but that the effects of air pollution are nevertheless small compared to other risk factors.
Dr Anna Hansell added: “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.”