Cancer And Inner-City Pollution: Is There A Link?

Air pollution is a major contributor to the global burden of disease, with 99% of the world's population breathing unhealthy air. Outdoor air pollution, particularly particulate matter (PM) in outdoor air, has been linked to lung cancer incidence and mortality. Epidemiological evidence on the link between outdoor air pollution and other types of cancer is more limited, although adverse associations have been reported in an increasing number of studies.

Outdoor air pollution is caused by emissions from industry, power generation, transportation, and domestic burning. It includes gaseous pollutants such as sulfur dioxide, nitrogen dioxide, carbon monoxide, and volatile organic compounds, as well as PM, which can be directly emitted or formed in the atmosphere from primary pollutants. PM, especially fine particulate matter (PM2.5), can penetrate deep into the lungs and enter the bloodstream, leading to serious health effects.

While air pollution is a significant risk factor for lung cancer, the relative risk of cancer from air pollution is small compared to other factors such as smoking. In the UK, for example, outdoor air pollution causes about 10% of lung cancer cases, while smoking accounts for about nine times more cases. However, it is important to note that air pollution also has other adverse health effects, including respiratory and heart diseases.

To reduce the cancer risk from air pollution, regulatory measures, such as the World Health Organization's air quality guidelines, have been put in place. Additionally, individual actions, such as reducing vehicle emissions by walking, wheeling, or cycling, can contribute to lowering air pollution levels.

Outdoor air pollution and lung cancer

Outdoor air pollution is a major contributor to the global burden of disease, with 99% of the world's population breathing unhealthy air. It is a significant and far-reaching threat to public health, with evidence suggesting a link to cancer, stroke, respiratory and cardiovascular diseases, and other health issues.

Outdoor air pollution is caused by fine particulate matter (PM) – tiny airborne particles known as PM2.5 that are 2.5 micrometres in diameter or smaller. These particles are a mix of solid particles and liquid droplets that can penetrate deep into the lungs and even enter the bloodstream. PM is emitted from various sources, such as coal- and natural gas-fired plants, cars, agriculture, wildfires, wood-burning stoves, unpaved roads and construction sites.

There is substantial evidence from studies of humans and experimental animals, as well as mechanistic evidence, to support a causal link between outdoor air pollution, and especially PM, with lung cancer incidence and mortality. It is estimated that hundreds of thousands of lung cancer deaths annually worldwide are attributable to PM air pollution.

The International Agency for Research on Cancer (IARC) has classified outdoor air pollution and PM in outdoor air pollution as Group 1 human carcinogens for lung cancer. Evidence suggests that exposure to particle pollution can cause changes in airway cells that trigger lung cancer. Studies have shown that these changes are visible in about half of people with lung cancer who have never smoked.

The IARC has also classified household burning of coal and biomass fuel as Group 1 and Group 2A human carcinogens for lung cancer, respectively. Household burning of solid fuels, both coal and biomass, contribute significantly to high levels of outdoor air pollution, and thus to the burden of disease, in low- and middle-income countries.

In addition to lung cancer, there is some evidence to suggest that outdoor air pollution may be associated with other types of cancer, including bladder cancer and breast cancer. However, the epidemiological evidence for these links is more limited.

Outdoor air pollution may also be associated with poorer cancer survival, although further research is needed.

Indoor air pollution and lung cancer

Indoor air pollution is a significant contributor to lung cancer risk, especially among non-smoking women.

Indoor air pollution is caused by fine particulate matter, which is a mix of solid particles and liquid droplets that can penetrate deep into the lungs and even enter the bloodstream. Sources of indoor air pollution include coal- and natural gas-fired plants, cars, agriculture, wildfires, wood-burning stoves, unpaved roads, and construction sites.

In a study of Chinese women, those who cooked more than twice a day had a three-fold increased risk of lung cancer compared to those who did not cook regularly. The use of solid fuels for cooking and heating was also associated with a higher risk of lung cancer.

In addition, housing characteristics related to poor ventilation, such as single-story homes, less window area, no separate kitchen, and no ventilator, were associated with an increased risk of lung cancer.

Furthermore, indoor air pollution exposure was found to be correlated with higher levels of particulate matter, particularly during the winter months. Higher levels of particulate matter, especially smaller particles, were associated with an increased risk of lung cancer.

Air pollution and respiratory diseases

Air pollution is a major contributor to the burden of disease worldwide. It is estimated that seven million deaths were attributable to the joint effects of household and ambient air pollution. Exposure to air pollution can lead to respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma, as well as lung cancer.

The impact of air pollution on respiratory health

Air pollution can affect all parts of the body, including the lungs, heart, and brain. It can irritate the airways and increase respiratory symptoms such as coughing, phlegm, and wheezing. Studies have also linked particle pollution exposure to a variety of respiratory health effects, including respiratory infections, decreased lung function growth in children, and chronic loss of pulmonary function in adults. People with pre-existing respiratory conditions, such as asthma or COPD, are particularly vulnerable to the detrimental effects of air pollutants.

The role of particulate matter in respiratory diseases

Particulate matter (PM) is a major component of air pollution and includes solid particles or liquid droplets suspended in the air, such as dust, dirt, and smoke. PM can be divided into larger particles, such as dust and soot, and smaller "fine" particles, known as PM10 and PM2.5, which can reach the airways and breathing sacs in the lungs. Ultrafine particles, or nanoparticles, are the smallest fraction of PM and can cross into the bloodstream. These particles can carry toxic chemicals linked to cancer.

The impact of air pollution on lung cancer

Air pollution, particularly PM, has been linked to an increased risk of lung cancer incidence and mortality. Studies have found that exposure to air pollution can cause changes in airway cells that trigger lung cancer. Additionally, air pollution has been associated with poorer lung cancer survival and may interfere with cancer treatments.

Reducing the impact of air pollution on respiratory health

To reduce the harmful effects of air pollution, individuals can take measures such as reducing the time spent outdoors when air quality is poor, wearing masks, and using air cleaners indoors. For those with respiratory conditions, it is especially important to monitor air quality and take extra precautions. Additionally, on a broader scale, interventions such as transitioning to cleaner energy sources, promoting active transportation, and regulating industrial emissions can help improve air quality and reduce the impact of air pollution on respiratory health.

Air pollution and heart disease

Air pollution is a significant contributor to the global burden of disease, with 99% of the world's population breathing unhealthy air. It is a major risk factor for cardiovascular disease, which is the leading cause of death in the United States.

Cardiovascular disease is a general term for conditions that affect the health of the heart or blood vessels. The traditional risk factors for cardiovascular disease include male sex, older age, increased blood pressure, high total cholesterol, low HDL, and smoking. However, other factors such as diabetes and exposure to air pollution have also been found to contribute to the development of cardiovascular disease.

Research has shown that exposure to air pollution, particularly outdoor particle pollution, can exacerbate existing cardiovascular disease and increase the risk of cardiovascular events such as heart attacks, strokes, arrhythmias, and heart failure, especially in susceptible individuals such as the elderly or those with pre-existing medical conditions.

Fine particulate matter (PM2.5), which includes pollutants such as dust, dirt, soot, and smoke, can increase the risk of cardiovascular events. Short-term exposure to elevated levels of PM2.5 can trigger cardiovascular disease-related heart attacks and death, while long-term exposure can lead to increased risk of cardiovascular mortality and decreased life expectancy.

Sources of fine particle pollution include power plants, factories, automobiles, and wildfire smoke. These particles can remain in the atmosphere for days to weeks and can travel long distances, affecting air quality in cities and other areas far from the original source.

Preventative Measures

To reduce the risk of cardiovascular disease from air pollution, individuals can take precautions such as staying indoors during periods of low air quality, using air filtration systems, and consulting with healthcare professionals to understand local risks and resources.

On a broader scale, interventions to reduce air pollution exposure can include urban planning that prioritises active transportation (e.g., walking and cycling), the development of cleaner energy sources, and the implementation of policies to reduce vehicle emissions.

Air pollution, particularly fine particulate matter, has been linked to an increased risk of cardiovascular disease and related events. Addressing air pollution through individual, community, and regional interventions can help reduce the burden of cardiovascular disease and improve heart health.

Air pollution and pregnancy

Air pollution is a significant threat to public health, with 99% of the world's population breathing unhealthy air. This is especially true for pregnant women and neonates, who are particularly vulnerable to the effects of air pollution due to their unique physiology. During pregnancy, physiological changes such as increased oxygen consumption, minute ventilation, and cardiac output increase the amount of pollutants inhaled and circulated, leading to higher levels of exposure.

Air pollution has been linked to various adverse health outcomes in pregnant women and their developing babies. Studies have found that exposure to air pollution can increase the risk of maternal hypertensive disorders, postpartum depression, placental abruption, low birth weight, preterm birth, infant mortality, and adverse lung and respiratory effects. Pollutants can cross the placenta, affecting the health of the placenta itself and disrupting the baby's development.

The specific effects of air pollution depend on several factors, including the timing and duration of exposure, the specific pollutant, and individual vulnerability. Certain groups, such as those with low income or from minority groups, may also face additional risk factors that can intensify the effects of air pollution.

While the exact mechanisms by which air pollution causes adverse health effects are not fully understood, oxidative stress, epigenetic modifications, and immune dysfunction are thought to play a role. Comprehensive efforts are needed to address the health challenges posed by air pollution, including policies and actions to reduce air pollution and protect vulnerable populations.

To reduce the impact of air pollution during pregnancy, individuals can take measures such as evacuating to safer areas during periods of high air pollution, wearing face coverings when using cleaning products or paint, and avoiding going outside during very polluted times. Simple protection strategies, such as staying indoors, wearing face coverings outdoors, and using air filters, can help reduce the harmful effects of air pollution on pregnancy outcomes.

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