Air Pollution: Diseases And Disorders

Air pollution is a pressing issue that affects the health of millions of people worldwide. It is caused by a range of sources, from natural occurrences such as wildfires, dust storms, and volcanic eruptions to human activities like the burning of fossil fuels, industrial processes, and agriculture. The presence of contaminants in the atmosphere, including dust, fumes, gases, and smoke, can have detrimental effects on human health. Fine particulate matter, which is the most harmful type of air pollutant, can cause systemic damage as it penetrates deep into the lungs and enters the bloodstream, affecting almost every organ in the body. The health impacts of air pollution include respiratory issues, cardiovascular problems, brain disorders, and an increased risk of cancer. Vulnerable groups, such as children, the elderly, and those from lower socio-economic backgrounds, are more susceptible to the adverse effects of air pollution.

Particulate matter, carbon monoxide, and other pollutants

Particulate matter refers to a mixture of many chemical species composed of solids and aerosols. These particles vary in size, shape, and chemical composition and may contain inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the Earth's crust. The size of the particles is defined by their diameter for air quality regulatory purposes. Those with a diameter of 10 microns or less (PM10) are inhalable and can induce adverse health effects. Fine particulate matter, or particles that are 2.5 microns or less in diameter (PM2.5), are a subset of PM10 and are the main cause of reduced visibility (haze).

PM2.5 is associated with the greatest proportion of adverse health effects related to air pollution, both in the United States and worldwide. Short-term exposure to PM10 has been linked to the worsening of respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD), often leading to hospital visits. Long-term exposure to PM2.5 has been linked to premature death, particularly in those with chronic heart or lung diseases, and reduced lung function growth in children. The effects of long-term exposure to PM10 are less clear, but several studies suggest a link to respiratory mortality.

Carbon monoxide (CO) is another significant air pollutant. While very high levels of CO are unlikely to occur outdoors, elevated levels can be dangerous, especially for those with heart disease. People with heart disease already have a reduced ability to get oxygenated blood to their hearts, and elevated CO levels can further decrease oxygen delivery, leading to chest pain or angina.

Other common air pollutants include nitrogen oxide and sulphur dioxide, which are emitted through human activities such as burning fossil fuels, vehicle exhaust fumes, and emissions from agriculture and industry. These pollutants can aggravate breathing conditions, increase the risk of asthma attacks, and lead to more hospital admissions. Prolonged exposure to these pollutants has been linked to serious health conditions, including cancer, heart attacks, and strokes.

Respiratory diseases, including asthma and COPD

Air pollution is the presence of contaminants in the atmosphere, such as dust, fumes, gas, mist, odour, smoke or vapour, in quantities that can be harmful to human health. The main pathway of exposure from air pollution is through the respiratory tract, which can lead to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body, impacting the lungs, heart, and brain, among other organs.

Respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD), are among the most common health issues caused by air pollution. These diseases affect the airways and other structures of the lungs, causing restricted airflow and breathing problems.

Asthma is a respiratory condition characterised by reversible airway obstruction, meaning that the narrowing of the airways can be treated with inhaled medicines. Common symptoms of asthma include coughing, wheezing, and difficulty breathing. Asthma can be managed and controlled with long-term treatment, and by avoiding triggers such as smoke, fumes, dust, pollen, animal fur, and feathers.

COPD, on the other hand, is a progressive disease, meaning it usually worsens over time. It is characterised by fixed airway obstruction, which does not completely reverse with treatment. COPD causes damage to the lungs and a buildup of phlegm, resulting in symptoms such as chronic cough, breathlessness, and fatigue. While COPD cannot be cured, quitting smoking, and avoiding exposure to air pollution and second-hand smoke are crucial steps to slow down the progression of the disease and improve quality of life.

Both asthma and COPD are included in the broader category of Chronic Respiratory Diseases (CRDs), which also include occupational lung diseases and pulmonary hypertension. CRDs are caused by risk factors such as tobacco smoke, air pollution, occupational chemicals and dusts, and frequent lower respiratory infections during childhood. These diseases are not curable but can be managed through various treatments to improve breathing and reduce symptoms.

It is important to note that the impact of air pollution on respiratory health is not limited to these two conditions. Short-term exposure to air pollutants can lead to reduced lung function, respiratory infections, and aggravated asthma symptoms. Long-term exposure increases the risk of more severe health issues, including stroke, heart disease, lung cancer, and other non-communicable diseases.

Cardiovascular diseases, including stroke and heart disease

Air pollution is the presence of one or more contaminants in the atmosphere, such as dust, fumes, gas, mist, odour, smoke or vapour, in quantities and durations that can be harmful to human health. The World Health Organization (WHO) reported that ambient air pollution was responsible for 3.7 million deaths in 2012, representing 6.7% of total deaths worldwide.

Cardiovascular disease is a general term used to describe conditions affecting the health of the heart or blood vessels. It is the leading cause of death in the United States, with most deaths occurring in people over 65 years of age. One in three Americans has heart or blood vessel disease. The main risk factors for cardiovascular disease are male sex, older age, increased blood pressure, high total cholesterol, low HDL (high-density lipoprotein) and smoking. However, other factors such as diabetes and air pollution exposure have also been found to contribute to the development of cardiovascular disease.

Short-term exposure to air pollution can increase the risk of heart attack, stroke, arrhythmias and heart failure in susceptible people, such as the elderly or those with pre-existing medical conditions. The risk of death is greater from long-term exposure. Studies have shown that as PM10 levels increase by 10 μg/m3, there is a corresponding increase in hospitalisation for ischemic heart disease and congestive heart failure. Fine particulate matter, such as PM2.5, is a common and critical pollutant of both ambient and household air pollution, leading to negative health impacts. These fine particles can enter the bloodstream via the lungs and reach other organs, causing systemic damage to tissues and cells.

Current science suggests that air pollution aids the development and progression of atherosclerosis, a plaque buildup in the artery walls that causes heart disease. For those with heart disease, this buildup can result in blood clots that block the flow of blood and lead to a heart attack or stroke.

Neurological diseases, including cognitive impairment and depression

Air pollution is a pressing ecological issue that negatively impacts human health in numerous ways. Beyond its established links to respiratory and cardiovascular diseases, emerging evidence suggests that air pollution significantly affects the nervous system, increasing the risk of neurological disorders. This includes cognitive impairment and depression, which are the focus of this discussion.

Cognitive Impairment:

The impact of air pollution on cognitive function is an area of growing concern. Studies have found a correlation between exposure to fine particulate matter, specifically PM2.5, and cognitive decline. Inhalation of PM2.5 can interfere with mitochondrial structure and function, leading to reduced ATP production and subsequent neurodegeneration. This can result in conditions such as dementia and Alzheimer's disease (AD). Lo et al. discovered that long-term exposure to ambient air pollution, particularly O3, was significantly associated with cognitive impairment in elderly individuals. Furthermore, air pollution has been linked to impaired brain development in children, with potential long-term consequences for cognitive abilities.

In addition, air pollution can affect cognitive function by disrupting the insulin signaling system, leading to neural hyper-insulinemia, glucose resistance, and amyloid beta accumulation. Glucose resistance is associated with memory loss and hippocampal cell atrophy, further contributing to cognitive decline. Moreover, exposure to certain pollutants, such as manganese, has been linked to progressive cognitive impairment and memory impairment in adults.

Depression:

Air pollution has also been implicated in the onset and progression of depressive disorders. Studies have found associations between exposure to PM2.5, PM10, and nitrogen dioxide (NO2) and higher levels of depression. The mechanism underlying this relationship may be related to the ability of these pollutants to increase reactive oxygen species, causing oxidative stress and inflammation in the brain, which can lead to neuron damage and disruptions in neurotransmitter systems. This, in turn, can increase susceptibility to depressive symptoms. Additionally, air pollution may exacerbate anxiety, which is often a contributing factor to depression.

The link between air pollution and depression is further supported by research showing a correlation between air pollution and increased cortisol levels. Cortisol is a stress hormone that plays a significant role in cognition and depression. When the hypothalamus and pituitary gland are stimulated by air pollution, it leads to increased secretion of cortisol, which can have detrimental effects on mental health, including the development of depressive disorders.

Cancer, including lung cancer

Air pollution is a significant and far-reaching threat to public health, with 99% of the world's population breathing unhealthy air, according to the World Health Organization (WHO). Fine particulate matter, including soil, dust, soot, and smoke, is a common and critical pollutant of both ambient and household air pollution, leading to negative health impacts. These particles are so small that they can penetrate deep into the lungs, enter the bloodstream, and travel to organs, causing systemic damage to tissues and cells.

In 2013, the International Agency for Research on Cancer (IARC) classified outdoor air pollution and particulate matter (PM) with an aerodynamic diameter of less than 2.5 microns (PM2.5) as carcinogenic to humans. This classification was based on a review of all the available scientific evidence, which concluded that particulate matter causes lung cancer. The IARC's 2013 review specifically implicated PM2.5, which is a mixture of environmental pollutants from transportation, power generation, and other sources.

The Lancet Commission on pollution and health established that air pollution causes up to 29% of all lung cancer deaths. Studies have shown that changes in airway cells that trigger lung cancer are visible in about half of people with lung cancer who have never smoked. This is particularly concerning as smoking rates continue to decline, and the proportion of lung cancers in people who have never smoked is expected to increase.

In addition to lung cancer, air pollution has been associated with an increased risk of several other types of cancer, including breast, liver, and pancreatic cancer. A study in Hong Kong and Birmingham, UK, followed 66,280 residents aged 65 or older from 1998 to 2011 and found that exposure to fine particulate matter was associated with an increased risk of mortality for these cancers.

Reducing air pollution can directly mitigate the risk of developing lung cancer, and the actions to do so, such as increasing green spaces and cleaner energy sources, can also lead to a range of other health benefits. However, it is important to note that the levels of exposure to air pollution have increased significantly in some parts of the world, mainly in low- and middle-income countries with large populations.

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