The Effects Of Air Pollution And Neurodegenerative Disorders

Introduction

In recent years, the detrimental effects on human health from the rise in air pollution have been becoming increasingly apparent. Through research, new emerging evidence is suggesting a probable linkage between exposure to air pollution and health consequences, specifically with neurodegenerative disorders. 

There are multiple types of neurodegenerative disorders, such as Alzheimer's disease, Amyotrophic lateral sclerosis (ALS), and Parkinson's disease. They are generally characterised by progressive degeneration of the nervous system, which can deteriorate associated cognitive and motor functions. 

Understanding the potential link between air pollution and neurodegenerative disorders is of high importance for public health efforts aimed at mitigating the burden of these debilitating conditions on a community and individual level. 

Neurodegenerative disorders

Neurodegenerative disorders can be classified as a group of conditions with a gradual decrease in the function of the nervous system, especially in the brain and spinal cord. Due to the nature of the disorders, it leads to the gradual deterioration of neurons and their connections. According to a research article published in 2019, neurological disorders have been the leading cause of disability, and second leading cause of death worldwide.¹

Common neurodegenerative disorders include:

• Alzheimer's disease
• Parkinson's disease
• ALS 
• Lewy body dementia
• Huntington's disease

Depending on the anatomical area affected and the nature of the disease, symptoms and signs may vary:

• If the brain is primarily affected by the degeneration of neurons, then dementia-related symptoms can be exhibited which include confusion, memory loss and behavioural changes
• If the myelin, or the sheath covering the nerve, gets affected then symptoms related to demyelination can be seen such as numbness, pain and muscle spasms
• If a specific area of the brain responsible for producing dopamine is affected, then it can result in the reduction of dopamine leading to Parkinson-like symptoms such as slowed movements, shaking and balance-related issues

The causes of these disorders are multifactorial with a strong disposition related to genetic and lifestyle factors. However, there is also a role of environmental pollutants, particularly air pollution, that has gained attention.

Air pollution and neurotoxicity

Air pollution is a complex mixture of multiple matter, gases, and chemical pollutants that are emitted from various sources such as vehicle exhaust, industrial emissions, and combustion processes. Constant exposure to these air pollutants can result in carcinogenic effects while also penetrating the central nervous system, leading to neurotoxic (damaging the neurons) effects and contributing to neurodegeneration. 

When air pollutants are inhaled, they are transported around the body in the blood and cross the blood-brain barrier, a selective layer protecting the brain from substances circulating in the blood. The contact of air pollutants with the brain can affect its functioning and eventually lead to neurodegeneration. 

There are heavy metals such as lead, mercury, and arsenic which are air pollutants. They particularly have neurotoxic properties and can accumulate in the brain over time. These metals can interfere with neuronal function, disrupt neurotransmitter signalling, and promote the formation of oxidative stress, leading to eventual cognitive impairment.

Epidemiological evidence

Apart from general concern, there is epidemiological evidence linking air pollution to neurodegenerative disorders in recent years, providing valuable insights into the association between environmental exposures and neurological health outcomes. 

Air particulate matter (PM) is a mixture of many chemical species including solids and small droplets of liquid. Particles vary widely in size, shape and chemical composition, and may contain inorganic ions, metallic compounds and organic compounds. These particles are characterised by their individual diameter for air quality regulations. Those with a diameter of 10 microns or less (PM10) are inhalable into the lungs and can result in deterioration in health.

A study published by the European Journal of Public Health involving more than 24,000 subjects, showed that there is an increased risk of neurodegeneration, specifically with particular matter 10 pollution.² Furthermore, another study explored and concluded that PM 2.5 also has been shown to cause neurodegeneration, specifically increasing the chance of Alzheimer's and Parkinson's disease.³

Research in this area is relatively preliminary but there is strong leading evidence that exposure to air pollution during periods of development may increase the risk of neurodegenerative diseases later in life.

Biological mechanisms

The biological mechanisms involve complex interactions between environmental pollutants and the central nervous system.

Airborne pollutants can trigger inflammatory responses in the brain. Inhalation of pollutants can activate the release of pro-inflammatory proteins such as cytokines. Prolonged exposure to air pollutants may lead to chronic inflammation, consequently leading to neurological dysfunction and neurodegeneration.⁴

Oxidative stress is another pathway that can contribute to neurodegeneration. Air pollutants contain oxidative stress-inducing compounds that can overwhelm antioxidant defences in the brain. Prolonged oxidative stress leads to damage of the cellular components such as lipids, proteins, and DNA and ultimately neurological deterioration.⁵

Finally, air pollution can compromise the blood-brain barrier, which is a selective barrier that controls the passage of molecules between the bloodstream and the brain. Exposure to pollutants can disrupt the anatomy on a cellular level allowing pollutants to enter the brain easily. Through this dysfunction it can allow for the infiltration of inflammatory cells and neurotoxic substances into the brain, exacerbating neuroinflammation and neuronal damage.⁵

Public and clinical health support

The growing evidence linking air pollution to neurodegeneration highlights the importance of implementing policies and regulations aimed at reducing air pollution levels. Governments need to implement stricter emission standards and clean air initiatives as well as promote sustainable transportation and energy sources to mitigate environmental pollution and protect neurological health.

Through public awareness campaigns and educational initiatives, awareness can be raised about the adverse effects of air pollution on neurological health and encourage individuals to take steps to reduce their exposure. Providing up-to-date information about the sources of air pollution, the health risks associated with exposure, and practical strategies for minimising exposure can encourage individuals to make informed choices.

Furthermore, routine screening for air pollution exposure and assessment of environmental risk factors may help identify individuals at increased risk of neurodegeneration, especially in areas that have concentrations of air pollution. Identifying modifiable risk factors and finding methods of minimising them can also help with the incidence of neurodegenerative disorders. 

A multidisciplinary approach that integrates and involves the public health, clinical care, environmental science, and community sectors is essential for developing effective strategies. Communication on the community front with the healthcare and government workers can allow them to develop strategies such as screening clinics, education, incentives to reduce emissions and providing general support. 

From a scientific perspective, continued research is needed to better understand the mechanisms underlying air pollution-induced neurodegeneration, while identifying susceptible populations, and evaluating the effectiveness of current interventions. Different forms of research can provide insights into the long-term effects of air pollution exposure on neurological outcomes and inform evidence-based interventions and policies.

FAQs

How can I reduce my exposure to air pollution and protect my neurological health?

There are multiple ways to limit exposure to air pollution. Avoid outdoor activities during times of high pollution and if going outside use face masks. While inside, usage of indoor air purifiers can help on a community level by advocating for cleaner air policies. Apart from this, maintaining a general healthy lifestyle through diet and exercise can also maximise neurological health. 

Are certain populations more vulnerable to the neurological effects of air pollution?

Certain populations, specifically what are normally considered vulnerable populations, such as older adults, children, and individuals with pre-existing health conditions, may be more susceptible. Workers who are more prone to exposure to smog, smoke and other air pollutants may also be at a higher risk for neurodegenerative disorders.

Summary

Neurodegenerative disorders represent a significant public health challenge with continuous evidence suggesting a strong linkage between exposure to air pollution. Air pollution contains neurotoxic components such as fine particulate matter, heavy metals, and volatile organic compounds, which can infiltrate the brain, induce inflammation, and oxidative stress, and disrupt neuronal function.

Through various kinds of studies, there have been associations shown between long-term exposure to air pollution and increased risk of neurodegenerative diseases, highlighting the importance of addressing environmental factors in the prevention and management of these debilitating conditions for both the current and future generations. Understanding this linkage and biological mechanisms underlying air pollution-induced neurodegeneration can help in the implementation of interventions to reduce air pollution exposure and mitigate the burden on individuals and society.