Does Air Pollution Cause Lung Cancer?
by Dr. C.H. Weaver M.D. 12/2018
According to the World Health Organization (WHO) the answer is yes. The WHO has classified air pollution as a human carcinogen (like tobacco smoke, asbestos and arsenic) and is calling it a leading cause of cancer deaths globally. (1)
For years, air pollution has been linked to a variety of ailments. Some compounds, such as diesel exhaust, have already been labeled as carcinogens. (2) But this is the first time that air pollution, in its entirety, has been classified as a carcinogen.
Air pollution is a broad term used to refer to a complex mix of particulates in the air. Air pollution can be caused by transportation, power generation, industrial or agricultural emissions and residential heating and cooking. The composition and levels of air pollution vary over space and time—but the International Agency for Research on Cancer (IARC), a scientific working group of the WHO, was tasked with evaluating the air that everyone breathes, rather than focusing on specific pollutants. As such, they concluded that air pollution poses a risk to anyone exposed to it.
The IARC reviewed thousands of studies on air pollution and found that exposure to air pollution increased the risk of lung cancer and bladder cancer. Depending on the level of exposure, the risk may be equivalent to breathing secondhand tobacco smoke. The group concluded that air pollution is a leading environmental cause of cancer deaths.
Research has indicated that exposure to air pollution has risen dramatically in some parts of the world, including Asia, South Asia, North Africa, Mexico, Central America, and eastern North America.
The agency concluded that air pollution is carcinogenic to humans, which is the highest of the agency’s four-level classification system. They note that both air pollution and particulate matter (a component of air pollution) will now be classified among its Group 1 human carcinogens.
What Does the Research Show?
Lung Cancer Risk and Traffic-related Air Pollution
Researchers report a modest association between air pollution resulting from traffic and risk of lung cancer. These findings were recently published in the journal Cancer Epidemiology, Biomarkers & Prevention. (3)
Researcher are trying to determine which air pollutants may be associated with lung cancer. Air pollutants include byproducts of fossil fuel combustion, exhaust from motor vehicles and diesel engines, and emissions from power plants and industrial centers.
A Danish study evaluated lung cancer risk in relation to levels of traffic-related air pollution as measured by concentrations of nitrogen oxides. The study involved 679 people with lung cancer and 3,481 people without lung cancer. Average exposure to nitrogen oxides was estimated based on residential address. The analysis accounted for other known or potential lung cancer risk factors such as smoking, educational level, body mass index, and alcohol consumption.
The researchers reported a modest association between traffic-related air pollution and lung cancer risk (37% increase in risk for every100 μg/m3 increase in nitrogen oxides).
Exposure to Air Pollution Increase Risk of Lung Cancer & Cardiopulmonary Disease
According to an article published in the Journal of the American Medical Association, evidence suggests that long-term exposure to air pollution may increase an individual’s risk of death by lung cancer, cardiopulmonary disease and other illnesses.
Some of the most damaging air pollution is caused by the burning of fuel, which results in fine particles (particulate) and sulfur oxide. Breathing high levels of fine particulate and/or sulfur oxide versus “clean” air on a day-to-day basis has been associated with an increased risk of illness. However, the long-term side effects of breathing polluted air have not been conclusively explored.
Researchers recently conducted a study evaluating the relationship between air pollution (fine particulate and sulfur oxide) exposure and death due to lung cancer, cardiopulmonary disease and other illnesses. Participants completed a risk factor questionnaire investigating age, sex, race, weight, height, smoking history, education, marital status, diet, alcohol consumption and occupational exposures. Air pollution data for metropolitan areas throughout the United States was also investigated. Over a 16-year period, researchers assessed risk factor data including metropolitan air pollution data, participant vital status and cause of death for approximately 500,000 adults. Exposure to air pollution was associated with an increased risk of death due to lung cancer, cardiopulmonary disease and other illnesses. For each unit of increase in exposure to fine particulate air pollution, the risk of death increased by 8% for lung cancer, 6% for cardiopulmonary disease and 4% for other illnesses.
These results indicate that long-term exposure to air pollution may increase an individual’s risk of death by lung cancer, cardiopulmonary disease and other illnesses. (4)
Reducing Air Pollution Improves Health
A study of air quality in six US cities reported that fine particulate air pollution is linked with death from cardiovascular disease and possibly lung cancer, and that the overall death rate decreases when pollution decreases. These results were published in the American Journal of Respiratory and Critical Care Medicine. (5)
Fine particulate air pollution is pollution that consists of tiny particles no larger than 2.5 µm (a µm is one millionth of a meter) in diameter. These very small particles tend to cause more health problems than larger particles because they can penetrate further into the lungs. Sources of fine particulate air pollution include combustion from motor vehicles and power generation.
Several previous studies have linked high concentrations of fine particulate air pollution with an increased risk of death. To explore the extent to which reductions in air pollution reduce death rates, researchers evaluated information from the Harvard Six Cities Study.
This study assessed the levels of fine particulate air pollution in six US cities: Watertown, MA; Kingston and Harriman, TN; St. Louis, MO; Steubenville, OH; Portage, Wyocena and Pardeeville, WI; and Topeka, KS. Study participants from each city were enrolled into the study between 1974 and 1977, and their health status has been assessed over time.
Air pollution levels and death rates were assessed for two different time periods: 1974-1989 and 1990-1998.
- During both time periods, higher levels of fine particulate air pollution were linked with a higher overall death rate as well as a higher rate of death from cardiovascular disease. There was also some suggestion of an increased risk of death from lung cancer.
- Air pollution levels dropped over time in all six cities. The decline in pollution was most dramatic in those cities that had the highest levels at the start of the study.
- Overall death rates dropped as air pollution improved. The decline in the overall death rate appeared to be due to a decline in deaths from cardiovascular and respiratory disease.
- As air pollution improved, there was no evidence of a decline in lung cancer deaths. Lung cancer is likely to be less reversible than cardiovascular or respiratory disease. In addition, lung cancer takes many years to develop, and may not be as responsive to recent changes in exposure.
The researchers conclude that “These findings suggest that the mortality effects of long-term air pollution may be at least partially reversible over periods of a decade.”
Straif K, Cohen A, Samet J, et al. IARC Scientific Publication No. 161.
Raaschou-Nielsen O, Bak H, Sørensen M, et al. Air Pollution from Traffic and Risk for Lung Cancer in Three Danish Cohorts. Cancer Epidemiology, Biomarkers & Prevention. 2010; 19(5):1284-91.
(Journal of the American Medical Association, Vol 287, No 9, pp 1132-1141, 2002)
Laden F, Schwartz J, Speizer FE et al. Reduction in Fine Particulate Air Pollution and Mortality: Extended Follow-Up of the Harvard Six Cities Study. American Journal of Respiratory and Critical Care Medicine. 2006. 173:667-672.