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People who have never smoked, but who live in areas with higher air pollution levels, are roughly 20% more likely to die from lung cancer than people who live with cleaner air, researchers conclude in a new study.
"It's another argument for why the regulatory levels for air pollutants should be as low as possible," said Francine Laden from the Harvard School of Public Health, who was not involved in the research.
Though smoking is the number one cause of lung cancer, about 10% of people who develop lung cancer have never smoked.
"Lung cancer in people who have never smoked is an important cancer. It's the sixth leading cause of cancer in United States," said Michelle Turner, the lead author of the study and a graduate student at the University of Ottawa.
Zip codes
Previous estimates of how many non-smokers get lung cancer range from 14 to 21 out of every 100,000 women and five to 14 out of every 100,000 men.
The fine particles in air pollution are thought to be a risk factor for lung cancer, but researchers had not clearly distinguished their impact from that of smoking.
In this study, Turner and her colleagues analysed data on more than 180,000 non-smokers that had been collected over a period of 26 years. During the study period, 1,100 people died from lung cancer.
The participants lived in all 50 states and in Puerto Rico, and based on their zip codes, the researchers estimated how much air pollution they were exposed to – measured in micrograms of particles per cubic meter of air.
Fine particles
Pollution levels in different locations ranged from a low of about 6 mcg/m3 to a high of 38 mcg/m3. The levels dropped over time, however, from an average of 21 in 1979 - 1983, to 14 in 1999 - 2000, producing an overall average pollution level of 17mcg/m3 across the study period.
After adjustment for other cancer risk factors, such as second-hand smoke and radon exposure, the researchers found that for every additional 10 mcg/m3, a person's risk of lung cancer rose by 15% to 27%.
The increased risk for lung cancer associated with pollution is small in comparison to the 20-fold increased risk from smoking. And the study doesn't prove that the pollution caused the cancer cases, but there's lots of evidence that exposure to fine particles increases cardiopulmonary mortality, Turner told Reuters Health.
Indoor pollution
Fine particles in air pollution can injure the lungs through inflammation and damage to DNA, Turner's team writes in its report, published online in the American Journal of Respiratory and Critical Care Medicine.
Previous research has suggested similar conclusions. A study in China, for example, found an increased risk of lung cancer attributed to indoor air pollution from burning coal and wood to heat homes (see Reuters story, December 7, 2009). And several European studies have linked levels of soot and vehicle exhaust to lung cancer in non-smokers.
Laden noted that the pollution levels associated with the increased risk of cancer in the current study are not uncommon in the US
"These levels are within the (regulatory) standards," Laden told Reuters Health. "We're not talking about people who live in a really polluted place with no pollution control."
(Reuters Health, October 2011)
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