Air Pollution: A Silent Killer?

Air pollution is a major environmental and health risk, causing millions of deaths each year. It is the presence of one or more 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, but it can also enter the bloodstream and circulate throughout the body. This can lead to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells, impacting the lungs, heart, brain and other organs, and ultimately leading to disease.

Both short- and long-term exposure to air pollution can lead to a wide range of diseases, including stroke, chronic obstructive pulmonary disease, lung cancer, aggravated asthma, lower respiratory infections, heart disease, neurological disorders, gastrointestinal disorders, and kidney disease.

Cardiovascular diseases

Air pollution has been linked to an increased risk of cardiovascular diseases, with short- and long-term exposure to particulate matter being associated with a higher risk of heart attacks, strokes, arrhythmias, and heart failure in susceptible people. Cardiovascular disease is a general term used to describe conditions affecting the health of the heart or blood vessels.

Traditional Risk Factors

Traditional risk factors for cardiovascular disease include male sex, older age, increased blood pressure, high total cholesterol, low HDL, and smoking.

Air Pollution and Cardiovascular Disease

Fine particulate matter, with diameters of less than 2.5 micrometers, can increase the risk of cardiovascular events. Research has found that exposure to increased concentrations of fine particulate matter over a few hours to weeks can trigger cardiovascular disease-related heart attacks and death. Longer-term exposure can lead to an increased risk of cardiovascular mortality and decreased life expectancy.

Sources of Fine Particulate Matter

Sources of fine particulate matter include power plants, factories, automobiles, and wildfire smoke. These particles can be found year-round and contribute to air quality problems in many major cities. Some particles can remain in the atmosphere for days to weeks and can travel hundreds or thousands of miles, influencing the air quality of regions far from the original source.

Populations at Risk

Populations at an elevated risk of experiencing the adverse health effects of air pollution include the elderly, people with underlying coronary or pulmonary disease, people of lower socioeconomic status, and people with diabetes.

Mechanisms Linking Air Pollution and Cardiovascular Disease

The putative biological mechanisms linking air pollution to heart disease involve direct effects of pollutants on the cardiovascular system, blood, and lung receptors, and/or indirect effects mediated through pulmonary oxidative stress and inflammatory responses. Direct effects may occur via agents that readily cross the pulmonary epithelium into the circulation, such as gases, and possibly ultrafine particles, along with soluble constituents of fine particulate matter.

Inhalation of air pollutants induces pulmonary oxidative stress and inflammation, with exposure to fine particulate matter producing an inflammatory response in the lungs and an increase in blood factors that affect coagulation. Oxidative stress occurs after exposure to ultrafine carbon black and diesel exhaust particles, ambient fine particulate matter, and cigarette smoke.

Health Effects of Air Pollution

Air pollution has been linked to an increased risk of the following cardiovascular diseases:

• Myocardial infarction
• Stroke
• Heart failure
• Arrhythmia
• Sudden death
• Ischemic heart disease
• Congestive heart disease
• Atherosclerosis
• Hypertension

Neurological disorders

Air pollution is a major global public health problem, and it is the single largest environmental health risk in Europe. It is a risk factor for all-cause mortality and specific diseases, including stroke, ischaemic heart disease, chronic obstructive pulmonary disease, lung cancer, pneumonia, and cataract.

Air pollution can also cause neurological disorders, including neural inflammation, neurodegeneration, and cerebrovascular barrier disorder. The mechanisms underlying the neurological diseases induced by various components of air pollutants remain unclear, but there is a growing body of evidence that links air pollution to an increased risk of neurological and psychiatric disorders such as cognitive decline, dementia, anxiety, depression, schizophrenia, and attention deficit hyperactivity disorder.

A recent study found that air pollution was significantly associated with an increased risk of hospital admissions for several neurological disorders, including Parkinson's disease, Alzheimer's disease, and other dementias, in a long-term study of more than 63 million older U.S. adults. The study, which was the first nationwide analysis of the link between fine particulate (PM2.5) pollution and neurodegenerative diseases in the U.S., found that for each 5 microgram per cubic meter of air (μg/m3) increase in annual PM2.5 concentrations, there was a 13% increased risk for first-time hospital admissions for Parkinson's disease and Alzheimer's disease and related dementias. This risk remained elevated even below supposedly safe levels of PM2.5 exposure, according to current U.S. Environmental Protection Agency standards.

The specific disease outcomes most strongly linked with exposure to air pollution are still being studied, but the available evidence suggests that air pollution can cause various neurological conditions and diseases.

Gastrointestinal disorders

Air pollution is a major threat to health and climate across the globe. It 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 injurious to human health. The main pathway of exposure from air pollution is through the respiratory tract. However, air pollutants can also be ingested from food, which can be easily contaminated.

Air pollution has been linked to various gastrointestinal disorders, including inflammatory bowel disease (IBD), appendicitis, irritable bowel syndrome (IBS), and enteric infections in infants. It is thought that air pollution changes the gut microbiome, leading to inflammation and an immune response. The gut microbiome is made up of billions of bacteria, and while there is no clear answer as to what a healthy gut microbiome looks like, it is widely accepted that environmental factors, such as diet, can alter it.

A study by Gilaad Kaplan, an associate professor at the University of Calgary, analysed data from over 900 cases of IBD in the UK over three years. Kaplan found that Crohn's disease was more commonly found in young people with higher exposures to nitrogen dioxide. Kaplan has also found links between air pollution and appendicitis and abdominal pain.

Another study found that exposure to particulate matter (PM) can trigger the onset of gastrointestinal disease. Mice were given a high oral dose of PM for up to 14 days, and another group was fed PM for 35 days. The mice exposed to PM for a shorter time had altered immune gene expression, evidence of inflammation, and heightened immune response in the small intestine, as well as increased gut permeability. The mice exposed for 35 days showed signs of inflammation in the colon and changes in their gut microbiome.

Ingested particulate matter has also been found to alter the gut microbiome composition and function. A study on IL-10−/− mice (whose colitis development depends on the gut microbiome) showed that particulate matter in their food led to significant changes in the relative amounts of Bacteroidetes, Firmicutes, and Verrucomicrobia. These changes in microbial abundance correlated with changes in short-chain fatty acid production, with increased concentrations of branched-chain fatty acids isobutyrate and isovalerate in the cecum.

Particulate matter has also been found to increase intestinal permeability, which has been associated with a number of diseases, including IBD and celiac disease. Intestinal inflammation has been linked to several chronic diseases in Western countries, including asthma, type 1 and 2 diabetes, and atherosclerosis.

Prevention and Management

To mitigate the impact of air pollution on digestive health, it is crucial to reduce exposure to environmental pollutants. This includes avoiding areas with high pollution levels, especially during peak times, and using masks and air purifiers when necessary. Maintaining good indoor air quality and regular physical exercise are also recommended. Consuming a balanced diet rich in fibre, antioxidants, and essential nutrients can strengthen the digestive system and boost immunity.

Respiratory problems

Air pollution is a major health concern, posing a serious threat to respiratory health. The respiratory tract is the main pathway of exposure to air pollution, and the inhalation of pollutants can lead to a range of respiratory problems, including:

Inflammation and Oxidative Stress

Fine particulate matter, such as PM2.5, can penetrate deep into the lungs and enter the bloodstream, causing systemic inflammation. Air pollutants can irritate the airways, leading to inflammation of the lungs and oxidative stress in cells throughout the body. This inflammation increases the responsiveness of the airways to irritants, such as allergens and gaseous pollutants, and may reduce lung function.

Immunosuppression

Constant exposure to air pollution can compromise the body's immune system, making it more susceptible to respiratory infections and diseases.

Mutagenicity and Carcinogenicity

Air pollution has been linked to the development of lung cancer. Ultrafine particles can carry toxic chemicals that are carcinogenic, and exposure to these pollutants can lead to cellular damage and increase the risk of cancer.

Respiratory Symptoms

Breathing polluted air can cause a range of respiratory symptoms, including shortness of breath, coughing, wheezing, and chest pain. It can also trigger asthma flare-ups and increase the risk of lung infections, such as bronchitis and pneumonia.

Chronic Respiratory Conditions

Long-term exposure to air pollution can lead to the development of chronic respiratory conditions, such as asthma and chronic obstructive pulmonary disease (COPD). Children exposed to air pollution are at an increased risk of developing asthma and COPD later in life. Additionally, air pollution can aggravate existing respiratory conditions, leading to more frequent hospitalizations and emergency department visits.

Cancer

Air pollution has been linked to lung cancer, with studies showing that exposure to air pollution increases the risk of developing lung cancer. 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.

According to the World Health Organization (WHO), 99% of the world's population breathes unhealthy air, and air pollution is now estimated to cause nearly seven million deaths per year. While smoking is a much bigger cause of lung cancer, air pollution is still a significant contributor, causing around one in ten cases in the UK.

In addition to lung cancer, there is also evidence to suggest a link between air pollution and breast cancer. A study by the National Institutes of Health found that living in an area with high levels of particulate air pollution was associated with an 8% increase in breast cancer incidence. This is a relatively modest increase, but significant given that air pollution is a ubiquitous exposure. The study also found that particulate matter pollution (PM2.5) was associated with a higher incidence of estrogen receptor-positive (ER+) breast cancer, suggesting that PM2.5 may affect breast cancer through an underlying biological pathway of endocrine disruption.

Furthermore, a study by researchers in Hong Kong and Birmingham, UK suggested that air pollution is associated with an increased risk of mortality for several types of cancer, including breast, liver, and pancreatic cancer. The study found that for every 10 micrograms per cubic meter (µg/m3) of increased exposure to PM2.5, the risk of dying from any cancer rose by 22%. For breast cancer, the mortality risk was 80% higher.

While more research is needed to fully understand the link between air pollution and cancer, the evidence suggests that air pollution is a significant risk factor for certain types of cancer, including lung and breast cancer.

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