A population-based study of lung cancer patients in California has shown that exposure to air pollutants nitrogen dioxide, ozone and airborne particles was associated with an increased risk of early death. Those living in areas with high levels of nitrogen dioxide (NO2) and particulate matter (both PM10 and PM2.5), especially those with lung cancer, live less, according to a study published in the journal Thorax.
Higher exposure to the pollutants nitrogen dioxide, ozone and airborne particles was associated with an increased risk of early death.
The association was strongest in patients with early stage disease, particularly adenocarcinoma, which accounts for 80 percent of lung cancer cases, the researchers said.
Researchers led by Sandrah Eckel of the department of preventive medicine at the University of Southern California in Los Angeles, analysed data from more than 352,000 people in California who were diagnosed with lung cancer between 1988 and 2009.
The researchers tracked the health outcomes of the sample population, whose details had been entered into the US California Cancer Registry, up until the end of 2011. They mapped participants' exposure to air pollutants to their residences using data from US Environmental Protection Agency's air quality monitoring stations.
Lung cancer is of several types and survival rates differ depending on when it is diagnosed. For patients with early stage disease, average survival time was shortest for those with small and large cell cancers (around 1.5 years) and longest for those with adenocarcinoma (around 5 years).
Almost half of the study participants (45.4 per cent) lived more than 1,500 metres away from a major interstate motorway. Less than 10 per cent lived within a 300 metre radius of one.
After taking account of these, and other potentially influential factors, the calculations showed that higher exposures to each of the four pollutants were associated with a correspondingly heightened risk of death and shorter average and 5-year survivals.
But the magnitude of heightened risk was greatest for patients with early stage disease, among whom average survival was 2.4 years for those with high PM2.5 exposure (at least 16 ug/m3) and 5.7 years for those with low exposure (less than 10 ug/m3), for example.
Overall, for patients with early stage disease, risk of death from any cause was 30 per cent greater for NO2; 26 pe cent greater for PM10; and 38 per cent greater for PM2.5. The impact of exposure to O3 was small (4 per cent).
As might be expected, survival rates of patients with advanced adenocarcinoma case was poor, irrespective of exposure to pollutants.
Besides pollution, there could be other potentially important risk factors such as an individual's lifestyle, smoking status, and alcohol intake; and the inability to capture road traffic pollution.
These are not part of the study and hence no firm conclusions can be drawn about cause and effect.