Article image

Air pollution increases the risk of all cancers, not just lungs

Although air pollution has long been established as a major risk factor for lung cancer (and an association with breast cancer risk has also been emerging), few studies have examined its effects on prostate, colorectal, and endometrial cancer risk. 

Now, a cohort study of millions of Medicare beneficiaries led by Harvard T.H. Chan School of Public Health has found that chronic exposure to fine particulate air pollutants (PM2.5) and nitrogen dioxide (NO2) may increase the risks of non-lung cancers – such as colorectal and prostate cancers – in older adults. 

Studying how air pollution causes cancers

The analysis revealed that even low levels of air pollution exposure may make people susceptible to developing these cancers, in addition to breast and endometrial cancers.

“Our findings uncover the biological plausibility of air pollution as a crucial risk factor in the development of specific cancers, bringing us one step closer to understanding the impact of air pollution on human health,” said lead author Yaguang Wei, a research fellow in Environmental Health at Harvard. “To ensure equitable access to clean air for all populations, we must fully define the effects of air pollution and then work towards reducing it.”

How the research was conducted 

The experts analyzed data from national Medicare beneficiaries aged 65 or older, collected between 2000 and 2016. All the participants were cancer-free for at least the first decade of the study period. 

The researchers created separate cohorts for different types of cancer – breast, colorectal, prostate, and endometrial – with between 2.2 million and 6.5 million subjects in each cohort. They conducted separate analyses to investigate the impact of air pollution on cancer risk for various subgroups. They used various factors including age, sex (for colorectal cancer only), race/ethnicity, BMI, and socioeconomic status. 

To estimate individual exposures to air pollution, the scientists developed a predictive map of PM2.5 and NO2 concentrations across the U.S. and linked it to beneficiaries’ residential ZIP codes.

What the researchers discovered 

The analyses revealed that chronic exposure to PM2.5 and NO2 increased the risk of developing colorectal and prostate cancers. However, they did not link to the risk of endometrial cancer.

In the case of breast cancer, NO2 exposure was associated with an increased risk, while the connection with PM2.5 was inconclusive. This is most likely due to variations in the chemical composition of PM2.5, which is a complex mixture of liquid and solid particles.

However, when the investigation was restricted to areas where air pollution levels were significantly below national standards and the composition of PM2.5 remained stable, their effect on breast cancer risk was higher.

Moreover, a greater risk of endometrial cancer was associated with exposure to both pollutants, even at lower pollution levels.

Disproportionate risks

In the analyses of risk by subgroups, the scientists found that communities with higher average BMI are likely to face disproportionately higher risk of all four cancers from exposure to air pollution from NO2, while Black Americans and those enrolled in Medicaid may be more susceptible of developing prostate and breast cancer, respectively, from PM2.5 exposure.

According to the researchers, even communities with seemingly clean air were not immune to cancer risk. Substantial associations between exposures to the two pollutants and the risks of developing all four cancers were identified even at pollution levels below the recently updated World Health Organization guidelines (which are lower than current U.S. standards).

U.S. air pollution standards are inadequate

“The key message here is that U.S. air pollution standards are inadequate in protecting public health,” concluded senior author Joel Schwartz, a professor of Environmental Epidemiology at Harvard. 

“The Environmental Protection Agency recently proposed stricter standards for PM2.5, but their proposal doesn’t go far enough in regulating this pollutant. Current NO2 standards are also woefully inadequate. Unless all of these standards become much, much stricter, air pollution will continue to result in thousands of unnecessary cases of multiple cancers each year.”

More about air pollution and cancers

Air pollution involves the presence of harmful substances or particulates in the Earth’s atmosphere. These pollutants, including both anthropogenic (human-generated) and natural compounds, can cause environmental degradation and serious health problems in both human and non-human populations.

Types of Air Pollutants

Air pollutants can be classified into two broad categories: primary and secondary pollutants. Identifiable sources directly emit primary pollutants. Secondary pollutants form in the air when primary pollutants interact or react with each other.

Primary Pollutants

Sources, which can be either natural or anthropogenic, directly emit these pollutants. They include substances like sulfur dioxide (SO2), carbon monoxide (CO), nitrogen oxides (NOx), particulate matter (PM), and volatile organic compounds (VOCs).

Secondary Pollutants

Secondary pollutants form in the atmosphere through complex chemical reactions involving primary pollutants. These include ozone (O3), which forms when sunlight reacts with nitrogen oxides and volatile organic compounds. Reactions with sulfur dioxide and nitrogen oxides respectively produce sulfates and nitrates, which are also secondary pollutants.

Sources of Air Pollution

Air pollution arises from both natural and human activities:

Natural Sources

Volcanic eruptions, wildfires, and dust storms contribute to air pollution by releasing gases and particulates into the atmosphere. Biological sources, such as pollen, mold, and bacteria, also contribute to air pollution.

Anthropogenic Sources

Human activities generate a significant portion of air pollution. These activities include industrial processes, fossil fuel combustion, vehicle emissions, deforestation, and agricultural practices.

Effects of Air Pollution

Health Effects

Long-term exposure to air pollution can cause chronic respiratory diseases, cardiovascular diseases, and lung cancer. Short-term effects can include irritation of the eyes, nose, and throat, shortness of breath, and allergic reactions.

Environmental Effects

Air pollution can lead to environmental degradation through acid rain, eutrophication, depletion of the ozone layer, and climate change. It can also harm wildlife, reducing biodiversity.

Economic Effects

The health problems caused by air pollution lead to increased healthcare costs. Additionally, air pollution can negatively impact tourism, outdoor recreational activities, and agricultural productivity.

Air Pollution Management

Managing air pollution requires coordinated efforts at local, national, and global levels:

Emission Control

This involves regulating and reducing the emission of pollutants through legislation, industrial process improvements, vehicle emission standards, and the promotion of cleaner fuels and renewable energy sources.

Air Quality Monitoring

Continuous monitoring of air quality helps identify pollution sources, enforce regulations, and inform the public about air quality conditions.

Public Awareness and Education

Raising public awareness and educating people about the causes and effects of air pollution can encourage actions that reduce personal emissions, such as using public transportation, recycling, and conserving energy.

Air pollution poses a significant threat to global health, ecosystems, and economies. However, through diligent efforts in emission control, air quality monitoring, and public education, it is possible to reduce the impacts of air pollution and promote a cleaner, healthier environment. The challenges posed by air pollution are pressing, but with a united global effort, they are not insurmountable.

The study is published in the journal Environmental Epidemiology.


By Andrei Ionescu, Staff Writer

Check us out on EarthSnap, a free app brought to you by Eric Ralls and

News coming your way
The biggest news about our planet delivered to you each day