Exposure to air pollution more than 30 years ago can impact an individual’s current risk of dying of respiratory disease, according to a report from the MRC-PHE Center for Environment and Health, Imperial College London.

Findings in the report, “Historic air pollution exposure and long-term mortality risks in England and Wales: prospective longitudinal cohort study,” published in the journal Thorax, were the result of one of the world’s longest air pollution studies, following 368,000 people in England and Wales over 38 years.

The research team estimated the levels of air pollution in the areas where the individuals lived at four different times — in 1971, 1981, 1991 and 2001 — using measurements from Britain’s historic air pollution monitoring networks. Researchers found the most elevated risks were for respiratory diseases like pneumonia, emphysema and bronchitis, although air pollution is also known to contribute to cardiovascular disease.

“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,” Dr. Anna Hansell, the study’s lead author, said in a press release. “We were surprised to find pollution has effects on mortality that persist over three decades after exposure.”

The researchers evaluated levels of black smoke and sulphur dioxide air pollution (produced mainly by burning fossil fuels like coal, oil, diesel, or gasoline) from 1971 to 1991, and PM10 (PM10, like black smoke, is a measure of small particles in the air) in 2001.  Since 2001, PM10, measuring particles smaller than 10 microns and with the ability to travel deep into the lungs, has been a common pollution measure. Industries, transport, construction activities, and even sea salt and soil agriculture are sources of PM10.

Pollution exposure risks were reported in units of 10 micrograms per cubic meter of air, and levels compared with data on disease and deaths. Findings suggested that every additional unit of exposure in 1971 translated to a 2 percent increased risk of pollution-related death at least 30 years later, or between 2002–09.

“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,” said Dr. Rebecca Ghosh, a study co-author from Imperial College’s School of Public Health.

Air pollution has been dramatically reduced in recent decades, with black smoke levels today about 20 percent of those of the 1970s, Dr. John Gulliver, another study co-author and a senior lecturer at the MRC-PHE Centre, said.

“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,” Dr. Hansell said. “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.”