Air Pollution And Lung Cancer: What's The Link?

Air pollution is a significant threat to public health, with 99% of the world's population breathing unhealthy air. It has been linked to several diseases, including lung cancer. In fact, nearly half of lung cancer cases in people who have never smoked are estimated to be related to air pollution.

Outdoor air pollution is a mixture of tiny dust-like particles and substances in the air that have the potential to negatively impact health. It can be artificial, such as fumes from vehicles or factories, or natural, such as wind-blown dust, radon, and ozone.

Research has shown that exposure to air pollution can lead to changes in airway cells that trigger lung cancer. These changes have been visible in about half of people with lung cancer who have never smoked.

The World Health Organization (WHO) has classified outdoor air pollution as a Group 1 human carcinogen for lung cancer, and efforts to reduce air pollution and mitigate its health effects are ongoing worldwide.

Outdoor air pollution and lung cancer

Outdoor air pollution is a major contributor to the global burden of disease, with most of the world's population residing in places where air pollution levels exceed the World Health Organization's (WHO) health-based air quality guidelines. Outdoor air pollution poses a significant public health challenge as it affects everyone and has numerous adverse health effects, including an increased risk of lung cancer.

Evidence suggests that exposure to outdoor air pollution, particularly fine particulate matter (PM2.5), increases the risk of developing lung cancer. PM2.5 refers to tiny particles in the air, such as soot, smoke, dust, and liquid droplets, that are small enough to penetrate deep into the lungs and even enter the bloodstream. These particles come from various sources, including vehicle exhaust, coal-fired power plants, industrial sources, wildfires, and wood-burning stoves.

Research has shown that outdoor air pollution can cause changes in airway cells that trigger lung cancer. Studies have found that these changes are visible in a significant proportion of people with lung cancer who have never smoked. The World Health Organization (WHO) has concluded that particulate matter in outdoor air is a cause of lung cancer.

The risk of lung cancer from outdoor air pollution is particularly high in low- and middle-income countries, where populations are often exposed to high levels of air pollution. Additionally, certain groups, such as children, the elderly, people with lung and heart disease, and people who work or exercise outdoors, may be at higher risk of developing lung cancer from outdoor air pollution.

To reduce the risk of lung cancer from outdoor air pollution, individuals can limit their activity outdoors when pollution levels are high and avoid exercising along heavily trafficked roads. On a larger scale, interventions such as reducing vehicle emissions, transitioning to cleaner energy sources, and increasing green spaces can help mitigate the impact of outdoor air pollution on lung cancer risk.

Indoor air pollution and lung cancer

Air pollution is a significant threat to public health, with 99% of the world's population breathing unhealthy air. It is a known cause of lung cancer, with nearly half of lung cancer cases in people who have never smoked estimated to be related to air pollution. Indoor air pollution, caused by second-hand smoke, burning wood or coal, radon gas, and other sources, is a key contributor to this risk.

Sources of Indoor Air Pollution

Indoor air pollution is caused by a variety of sources, with second-hand smoke from cigarettes, cigars, and pipes being a key contributor in the UK. Burning wood and coal for heating or cooking also adds to indoor air pollution. Radon gas is another important source of indoor air pollution that can increase the risk of lung cancer.

Health Risks of Indoor Air Pollution

Indoor air pollution has been linked to an increased risk of lung cancer, as well as other serious health conditions such as heart and lung diseases. Even passive smoking, or exposure to second-hand smoke, can cause lung cancer. The smoke from cigarettes can spread throughout a home and stay in the air for hours, putting everyone in the household at risk.

Reducing Indoor Air Pollution

To reduce indoor air pollution, it is recommended to avoid smoking indoors or, better yet, to quit smoking altogether. Using cleaner sources of energy for heating and cooking, such as switching from wood or coal to electricity or natural gas, can also help improve indoor air quality.

Global Efforts to Address Indoor Air Pollution

The World Health Organization (WHO) has developed action plans and issued global Air Quality Guidelines to address indoor air pollution. These guidelines include recommendations such as transitioning to cleaner energy sources, improving indoor ventilation, and reducing the use of solid fuels for cooking and heating, especially in low- and middle-income countries where indoor air pollution is a significant issue.

Air pollution and DNA damage

Air pollution has been linked to DNA damage, which is a prerequisite for most mutations and cancers. Outdoor air pollution has been found to cause DNA damage, and hundreds of studies have shown that the particulate and volatile fractions of outdoor air are mutagenic.

A few studies have used the single-cell gel electrophoresis (comet) assay to assess DNA damage associated with outdoor air pollution. By incorporating personal monitors, studies have shown that outdoor workers have higher levels of systemic DNA damage associated with levels of particulate matter and ozone.

Recent studies have confirmed that exposure to inhaled particles in outdoor air is associated with an increased risk of lung cancer. While the levels of ozone in outdoor air have also been associated with an increased risk of lung cancer and DNA damage, the causal nature of this relationship is unclear.

Air pollution has been found to cause oxidative stress, which can damage lipids, proteins, and DNA. Oxidative stress induced by reactive oxygen species (ROS) may increase the oxidation of 5-methylcytosine (5-mC) to 5-hydroxymethylcytosine (5-hmC). Global generation of 5-mC may also be decreased by air pollution-induced reductions in DNA methyltransferase (DNMT) expression.

Children and teens exposed to high levels of traffic-related air pollution have evidence of a specific type of DNA damage called telomere shortening. As the exposure to polycyclic aromatic hydrocarbons (PAHs) increases, telomere length decreases in a linear fashion. Children and teens with asthma are exposed to higher PAH levels than those without asthma.

Preventative Measures

Reducing air pollution prevents lung cancer and promotes overall health. Some preventative measures include:

• Increased green spaces
• Cleaner energy sources
• Active transportation (walking and cycling)

Air pollution and inflammation

Air pollution is a mix of solid particles and liquid droplets, including soil, dust, soot, and smoke. These particles are known as particulate matter or PM. They are emitted from sources such as coal- and natural gas-fired plants, cars, agriculture, wildfires, and wood-burning stoves.

Particulate matter can be harmful to our health. Bigger particles can irritate the eyes, nose, and throat, but our body's natural defenses help us to cough or sneeze them out. However, smaller particles are more dangerous. They can get trapped deep in the lungs and even enter the bloodstream, causing health issues.

While the precise way in which these particles cause cancer is still being researched, studies in mice suggest that air pollution may create an inflamed environment in the lungs, encouraging the proliferation of cells with existing cancer-driving mutations. This inflammation caused by particulate matter, rather than genetic mutations, may be the trigger for tumor growth.

In 2013, the World Health Organization (WHO) reviewed all the available science and concluded that particulate matter causes lung cancer. Furthermore, the Lancet Commission on pollution and health established that air pollution causes up to 29% of all lung cancer deaths.

Therefore, it is important to reduce exposure to air pollution and take steps to limit our contributions to local pollution sources.

Air pollution and epigenetic changes

Air pollution is a serious threat to human health, causing a range of diseases including lung cancer. Air pollution can induce epigenetic changes, which are linked with the etiology of various human diseases.

Epigenetic modifications

Epigenetics is the process where changes occur in gene functions without changing their underlying DNA sequences. DNA methylation and histone modifications are two key processes that alter gene functions without changing the DNA sequences. Micro-RNAs and non-coding RNAs (ncRNAs) also play a critical role in gene expression and contribute to epigenetic control.

Air pollution and DNA methylation

Emerging evidence suggests that air pollutants modulate epigenetic states, ranging from DNA methylation to miRNAs expression. Epithelial cells from the aerodigestive tract of heavy smokers exhibit aberrant methylation of multiple genes associated with the pathogenesis of lung cancer. DNA methylation pattern in the genome also gets altered upon exposure to certain pollutants. Direct exposure to PM2.5 also induces methylation of the p16 promoter (a tumour-suppressor gene) in alveolar epithelial cells as well as in the lungs of mice.

Air pollution and histones

The effect of air pollution on histone modification is well established. PAH exposure also induces histone modifications in mice. Cigarette smoke exposure is also associated with an increased expression level of DNMT1 and a decreased level of DNMT3B. Exposures to PM10 and DEP may cause an imbalance between histone acetyltransferase (HAT) and HDAC expression levels, as well as increase histone H4 acetylation in the promoter region of the specific genes, thereby generating inflammatory responses in human bronchial epithelial (HBE) cells.

Air pollution and miRNA

MicroRNAs are capable of regulating post-transcriptional gene expression and are thought to play a critical role in mediating biological responses to air pollution. A diverse class of ncRNAs, such as snoRNAs, miRNAs, siRNAs, exRNAs, piRNAs, and long ncRNAs, can influence transcription and translation processes and play significant roles in health and diseases.

Air pollution and non-coding RNA

Long non-coding RNAs (lncRNAs) are already emerging as potential regulators of air pollution-associated diseases. A recent work has shown that cigarette smoke extracts and PM2.5 treatment alter the expression level of a particular lncRNA, lung cancer progression-association transcript 1 (LCPAT1), in lung cancer cells. An experiment reveals that lncRNA LOC101927514 is linked with the PM2.5-induced inflammation in bronchial 16HBE cells that are used as a respiratory inflammation model. RNAi inhibition of lncRNA LOC101927514 reduces inflammation induced by PM2.5.

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