Living in areas with higher total exposures to harmful pollutants in the air, water and land is associated with greater odds of developing cancer, a US study suggests.
While plenty of previous research has linked individual pollutants to increased risks of specific types of cancer, the current study focused on how the combined effect of exposure to a variety of environmental contaminants may influence the risk of tumours.
Researchers examined the annual incidence rate for cancer diagnoses for each county in the US and found an average of 451 cases for every 100,000 people. Compared to counties with the highest environmental quality, counties that ranked the lowest had an average of 39 more cancer cases each year for every 100,000 residents.
"We do not experience exposures in a vacuum but rather are exposed to several exposures at any one time," said lead study author Dr. Jyotsna Jagai, of the University of Illinois at Chicago.
"We considered a broad definition of environmental exposures, which included pollution in the air, water, and land and also (man-made) and sociodemographic environmental factors," Jagai said by email. "We found that counties with poor overall environmental quality experienced higher cancer incidence than those counties with good overall environmental quality."
Cancer causes one in four deaths in the US each year, Jagai and colleagues note in the journal Cancer.
To assess the connection between environmental quality and cancer risk, the researchers examined county-by-county data on exposure to different pollutants from 2000 to 2005 and on new cancer diagnoses from 2006 to 2010.
Compared to men in counties with the highest environmental quality, men living in counties with the poorest environmental quality had an average of 33 more cases of all types of cancer for every 100,000 people. For women, living in counties with the worst environmental quality was associated with an average of 30 more cases of cancer for every 100,000 people.
In addition to looking at overall cancer rates, researchers also looked separately at the most common tumour types: lung, colorectal, prostate and breast malignancies.
Prostate and breast tumours were strongly associated with environmental quality, the study found. Living in the counties with the worst environmental quality was tied to about 10 more cases of these tumours for every 100,000 people.
One limitation of the study is that researchers may not have had enough years of data to fully assess the connection between pollutants and cancer because some slow-growing tumours might appear many years after exposure to pollutants, the authors note.
Researchers also lacked data on individuals' lifestyle factors that can influence cancer risk, such as alcohol use, exercise habits and nutrition.
"We do have to be careful about drawing conclusions from studies of neighborhood factors that lack detailed information on characteristics of individuals living in those neighborhoods because the observed associations could very well be due to attributes of the individuals rather than the environment itself," said Scarlett Lin Gomez, author of an accompanying editorial and a researcher at the Cancer Prevention Institute of California and the Stanford Cancer Institute.
"However, neighbourhood environment has been consistently shown to have its own impacts on health and on cancer over and above individual characteristics," Gomez said by email.