Does Air Pollution Cause Lung Cancer or Affect Survival?

woman standing outside in air pollution, a risk factor for lung cancer

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Air pollution has now been declared a cause of lung cancer after years of suspecting it may be a risk factor. In addition, particle pollution in the air appears to reduce survival in those who already have the disease. The degree of risk can vary significantly depending on where a person lives and works, the type of air pollution, and the size of particles. Even if you live in an area where pollution levels are higher, there are ways that you can reduce risk. Learn more about the role pollution plays in lung cancer in different regions of the world, the underlying mechanisms, and what you should know to protect yourself.

Importance

The importance of studying potential causes of lung cancer other than smoking cannot be understated. At the current time, roughly 20% of women who develop lung cancer have never touched a cigarette, and lung cancer is more likely to be diagnosed in non-smokers (those who have quit or who never smoked) than in smokers. Of great concern is that, while lung cancer has been decreasing overall, it is increasing in never smokers, especially young women.

Effect on Lung Cancer Risk

The type of air pollution referred to as particulate matter was classified as a human carcinogen according the the International Agency for Research on Cancer (part of the World Health Organization) in 2013. In this classification it's thought that particulate matter, rather than specific components of the air, are of most importance in lung cancer; it was air pollution as well as particular matter that were named as carcinogens, not specific compounds in the air. That said, some chemicals such as sulfur and nickel compounds may be of particular concern.

How Much Does it Raise Risk?

The role that air pollution plays in lung cancer risk varies with several factors. Overall, Global Burden of Disease Project data estimated that in 2010, air pollution resulted in 3.2 million deaths globally, 223,000 of which were due to lung cancer.

Geographical Differences

Globally, air pollution as a risk factor for lung cancer appears to be greatest in low and middle income countries that have large populations. In the U.S., it's been estimated that air pollution is responsible for roughly 5% of lung cancers in men and 3% of these cancers in women.

The estimate is higher in the U.K, where it's estimated that 10% of lung cancers are due to air pollution. This is true even though the level of air pollution in the U.K. is much lower than many other regions of the world.

Urban vs. Rural

Studies of geographical differences in the risk of lung cancer reveal that lung cancer is more common in urban areas and less common in rural areas, and this is to be expected.

Other Cancers Associated With Air Pollution

Air pollution as now been implicated not only as a cause of lung cancer, but a cause of bladder cancer as well.

Other Risks of Air Pollution

In addition to lung cancer, air pollution has been implicated in heart disease, asthma, COPD, and the chance of dying overall.

Effect of Air Pollution on Lung Cancer Survival

It appears that both ozone and particle pollution may affect survival with lung cancer in people who have already been diagnosed. Researchers looked at over 300,000 people with lung cancer in California between 1988 and 2009. Increased levels of air pollution (NO2, ozone, PM10, and PM2.5) were associated with poorer survival. The effect of air pollution on survival was most notable in people with early stage non-small cell lung cancer, particularly lung adenocarcinoma.

Defining Air Pollution

It's clear that air pollution is an important risk factor for lung cancer, but what exactly is it in air pollution that causes the damage that can lead to cancer?

There are two primary types of outdoor air pollution:

  • Ozone
  • Particle pollution: It's thought that particle pollution is most important as far as being a risk factor for lung cancer. Air born particles can be comprised of both chemical and biological matter and include both solid and liquid particles.

Sources

Sources of the compounds found in air pollution include vehicle exhaust, coal burning for heat or cooking, forest fires, diesel exhaust, power plants, wood stoves, and emissions from industrial and agricultural sources. Components can include both inorganic (metals) and organic chemicals, soil, and dust.

Particle Size and Risk

The size of particles in air pollution is very important in their role in cancer. It is the small particles (those less than 2.5 microns in diameter and less) that are of most concern. These particles cannot be seen by the human eye.

Larger particles are usually trapped in the mouth or nasal passages, or by cilia (the tiny hair like structures) in the larger airways. From there, they can be removed by coughing.

Mechanisms That Could Lead to Cancer

Cancer begins when a series of mutations in the DNA in a cell lead that cell to grow out of control.

Inflammation is thought to contribute to cancer. Any time a cell divides there is a small chance that a mistake will occur (a mutation or other alternation) in the DNA of the cell. Inflammation can lead to increased cell division. Studies have also shown that exposure to air pollution can cause "oxidative stress," that is, damage to the cells of the body caused by oxidation.

Many components in air pollution may directly damage DNA, causing the mutations and other genetic changes that can start a cell on the pathway to become a cancer cell.

Reducing Your Risk

As with many of the other risk factors for lung cancer, there are ways that people can reduce their risk.

Knowing Your Risk

The first step in reducing risk is to understand if you are at risk. Fortunately, the Environmental Protection Agency offers a tool called AirNow. With this tool, you learn about the air quality in your area based on your zip code.

Guidelines put for by the World Health Organization define the following as the upper limits of exposure based on particle size:

PM2.5 : 10 μg/m3 annual mean 25 μg/m3 24-hour mean

PM10 : 20 μg/m3 annual mean 50 μg/m3 24-hour mean

Reducing Outdoor Exposures

Choosing an area to live that has better air quality is one way to lower lung cancer risk, but is not always possible. And choosing a region to live based on air pollution levels alone overlooks many other important factors, such as the reduced stress associated with living in an area where you have strong social support. But even if you must live in an area with low air quality, hope is not lost. Some ways you can reduce your exposure include:

  • Avoiding outdoor exercise when air pollution levels are high
  • Choosing good areas to exercise (for example, you may wish to avoid running along congested highways with high levels of diesel exhaust)
  • Staying indoors (or working out at a health club) with windows close and the air conditioner running when the air quality index is elevated
  • Avoiding the tendency to idle in cars
  • Refraining from burning garbage

Reducing Indoor Exposures

Indoor air pollution is of concern as well, and can be even more dangerous that outdoor air pollution. Ways you can reduce your exposure include:

  • Switching from wood burning to gas fireplaces (if it's in your budget)
  • Refraning from burning anything other than properly aged wood in your fireplace (never burn garbage or paper containing ink)
  • Skip the wood stove
  • Purchasing some good houseplants: Research at NASA has found that several types of houseplants absorb a substantial amount of indoor air carcinogens

A Word From Verywell

Air pollution as a risk factor for lung cancer deserves in depth study. Unfortunately, the inaccurate belief that lung cancer is a smoker's disease has inhibited research into other causes. Perhaps with the increased public knowledge that lung cancer not only can and does occur in never smokers, but is actually increasing, will prompt the studies needed to evaluate other causes such as air pollution to a greater degree. Considering the number of people exposed to air pollution, even a small increase in risk translates to a very large number of cancers worldwide each year.

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Article Sources

  1. Eckel S, Cockburn M, Shu Y, et al. Air Pollution Affects Lung Cancer Survival. Thorax. 2016. 71(10):891-898. doi:10.1136/thoraxjnl-2015-207927

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