When we think of air pollution we just think it can cause some damage to our lungs.
Today, scientists have proven its far from the truth.
You will be shocked to know, air pollution which is known to claim 1 of every 9 deaths worldwide has a deeply negative impact on all parts of our body including the brain.
This article provides insights into the neurological problems caused by short- and long-term exposure to toxic air pollutants.
Numerous studies have established the relationship between contact with severely polluted air and the escalating rates of disease morbidity and deaths, typically caused by neurological disorders.
Before we explore more about how air pollution can impact one’s brain, a brief about what air pollution is.
Air pollution occurs when unwarranted volumes of deadly gases, particulates, and organic compounds enter the air.
Air pollution has been proved to have a devastating effect on the health of both humans and animals, alike. Based on the 2014 report issued by the World Health Organization, about 7 million people died, worldwide, due to air pollution in 2012.
The principal pollutants that affect air quality are gases like carbon dioxide, sulphur oxides, nitrogen oxides, carbon monoxide, and volatile organic compounds. Ammonia, chlorofluorocarbons, toxic metals, ammonia, and radioactive pollutants also contribute to air pollution.
Air pollution can progressively lead to the development of respiratory and cardiovascular complications, eye and skin irritation, neuropsychiatric disorders, and can even cause long-term diseases like cancer.
So, how can air pollution impact our brain and nervous system? The next section uses scientific studies to find it out.
Table of Contents
Neurological / Nervous System Problems Caused by Air Pollution
Extensive research has proved that air pollution is a risk factor for the development, exacerbation, and relapse of neurological disorders. Increased inflammation in the brain is one of the major reasons for the development of diseases of the central nervous system.
Air pollutants, such as ozone and particulate matter, cause oxidative damage leading to neurodegeneration and Alzheimer’s. Similarly, exposure to oxidative pollutants can also cause Parkinson’s disease and cerebrovascular stroke. The development and relapse of multiple sclerosis have also been linked with inhalation of gaseous particles that cause neuroinflammation. Air pollution is also marked as a risk factor for the neurodevelopmental disorders, such as autism.
1. Air Pollution Increases the Risk of Alzheimer’s disease
Alzheimer’s disease (AD), or Alzheimer’s, is a chronic neurodegenerative disorder that affects the central nervous system (CNS).
In 2015 alone, there were roughly 29.8 million people diagnosed with AD across the globe.
A majority (~70%) of the Alzheimer’s patients end up with dementia (complete loss of mental abilities). The earliest symptom is recurrent short-term memory loss.
Patients steadily experience disorientation (often get lost) as well as problems in communicating. Mood swings and behavioral problems also cause concern as patients become highly dependent on caregivers for day-to-day activities.
Other common symptoms of cognitive impairments include confusion, poor judgment, inability to make decisions, language disturbance, withdrawal, and paranoia.
A conclusive diagnosis of Alzheimer’s often requires a proper clinical assessment to confirm the presence of two characteristic features of the disease.
These include aggregates of the amyloid protein known as amyloid plaques as well as aggregates of tau proteins forming the neurofibrillary tangles.
Genetics plays a major role in the development of the disease and direct relatives of a patient have a cumulative lifetime risk of around 15%-30%.
Several other precursors and risk factors include a history of head trauma, depression, hypertension, and even environmental factors like pollution.
How does air pollution increase the risk of Alzheimer’s disease?
A 2012 review by the University of Nevada studied the role of air pollution in increasing the risk of developing Alzheimer’s.
The review stressed on the chronic oxidative damage caused by agents like ozone, nitrogen dioxide, and particulate matter (PM), which together promote the pathogenesis of the disease.
Another conclusive review that provided a link between the development of Alzheimer’s and increasing air pollution was carried out by the Lyon Neuroscience Research Center.
It was established that ozone pollution plays a major role in the neurodegeneration that is a hallmark of AD. Several experimental studies on rodents have shown that inhalation of ozone can adversely affect the CNS and bring about neuronal loss.
In 2013, the Rush Institute for Healthy Aging along with the Harvard School of Public Health conducted a study on the effect of air pollution on an elderly female population.
They concluded that a prolonged exposure to regularly experienced levels of PM2.5 (particulate matter with a diameter of 2.5µm) and PM2.5-10 (diameters within 2.5-10 µm) caused a severe cognitive decline in the elderly participants.
Air pollutants, such as ozone and PM2.5, increase the risk of developing Alzheimer’s by stimulating oxidative damage, neurodegeneration, and cognitive deficits.
2. Parkinson’s disease
Named after Dr James Parkinson who described the disease as ‘shaking palsy’, Parkinson’s disease (PD) is a progressive neurodegenerative disease marked by both motor (movement-related) as well as non-motor features.
The term ‘parkinsonism’ is a syndrome used to designate the motor characteristics of PD, which include bradykinesia (slowness of movement), tremor-at-rest, and muscular rigidity.
The motor complications of PD are ascribed to the loss of dopamine (a chemical messenger) neurons, whereas the presence of the specific non-motor symptoms also denotes the loss of other nerve cells.
While PD is the most typical cause of parkinsonism, an array of secondary causes also exists, including PD-like diseases and drug-induced causes.
Research suggests that the causative changes linked with PD may well start before the commencement of motor features and might be accompanied by a number of non-motor exhibitions, such as sleep disturbances, depressive mood disorders, and cognitive deficits. Parkinson’s is one of the most prevalent neurodegenerative disorders.
Several risk factors and genetic mutations are associated with the development of PD. These include air pollution which brings about oxidative stress through the formation of free radicals and a number of environmental toxins .
How does air pollution cause Parkinson’s Disease?
A 2017 review published in the journal, Reviews on Environmental Health, established that long-term exposure to air pollutants (ozone, carbon monoxide, sulphur dioxide, nitric oxide, and PM2.5) causes severe inflammation in the brain along with excessive oxidative stress, both of which are involved in the development and progression of Parkinson’s disease.
In a pilot study (small-scale research project) in Mexico City, which is one of the world’s most polluted metropolitan areas, a majority of the children exhibited abnormal lesions in their pre-frontal white matter i.e., abnormalities in the nerve endings found at the pre-frontal cortex of the brain.
As the pre-frontal cortex (front part of the brain) is affected by the inhalation of particulate matter (PM), individuals might expect a decline in cognitive functions and also experience problems with gait (manner of walking).
Exposure to air pollutants causes inflammation and oxidative damage in the brain along with affecting the pre-frontal cortex, all of which increase the risk of developing Parkinson’s.
3. Cerebrovascular Stroke
Cerebrovascular (relating to the blood vessels of the brain) disorders and stroke are significant causes of morbidity and mortality in children.
According to reports, they are amongst the top 10 causes of childhood death and are probably on the rise. Neonatal (newborn) stroke is quite common, with an occurrence of almost 63 per 1,00,000 live births.
An ischemic stroke happens if the flow of oxygenated blood is blocked by a portion of the brain. Without the required supply of oxygen, the brain tissue begins to die within a few minutes.
A hemorrhagic stroke is caused when a rupture in the cerebral arteries cause sudden bleeding in the brain and damages brain tissue.
Restricted blood flow in the brain is caused due to arterial stenosis (extreme narrowing). Atherosclerosis (arterial plaque formation) is one of the chief reasons behind the narrowing of the lumen of blood vessels which upsets the normal circulation of blood.
It also promotes the arterial obstruction or embolisms when the atherosclerotic plaques disintegrate and form clumps or clots.
Risk factors include viral infections, hypertension, as well as anemia. According to statistical reports, almost 1/3rd of the cases of childhood stroke occur due to infections.
Recently, degraded ambient air quality has also been reported as a risk factor for cerebrovascular complications.
How does air pollution cause Stroke?
A 2015 systematic review and meta-analysis by the University of Edinburgh stated that gaseous and particulate pollutants have a definite association with the number of hospital admissions and mortality due to stroke.
Both PM2.5 exhibited a particularly strong association with hospitalization due to cerebrovascular fatalities like a stroke.
It was inferred that inhalation of air pollutants cause damage to the arteries of the cerebral circulation, particularly by increasing arterial stenosis (narrowing).
This is brought about by oxidative stress and inflammation which accelerates plaque formation in the blood vessels, thereby, narrowing their diameters. Carotid artery stenosis is considered to be a major risk factor for ischemic strokes.
Particulate matter pollution brings about arterial stenosis, which is one of the major reasons behind cerebrovascular strokes.
4. Multiple Sclerosis
Multiple sclerosis (MS) is a long-lasting autoimmune neurological disease that affects the central nervous system (CNS).
MS targets the myelinated axons (nerve endings sheathed in myelin protein) in the CNS, degrading the myelin and the axons to severe extents.
The course of the disease is wide-ranging and random. In most patients, the disease is initially marked by incidents of adjustable neurological shortcomings and gradually followed by progressive and irreversible damage to the nervous tissue.
While the exact cause remains unknown, researchers have observed that it often involves a complex combination of genetic predisposition along with a non-genetic trigger, such as a pathogenic infection, metabolic disorder, or environmental factors like air pollutants, that come together to bring about an autoimmune condition wherein the immune cells attack the CNS.
How does air pollution cause multiple sclerosis?
In a 2017 hospital study carried out by the C. Mondino National Neurological Institute, it was found that increasing levels of air pollutants are associated with heightened inflammatory activities that promote MS.
It was found that PM2.5 and PM10 levels played a role in increasing the inflammation in the brains of MS patients who had participated in the study.
In another hospital study conducted by the Iran University of Medical Sciences, it was established that air pollution might also be a potential risk factor for the relapse of MS.
This phenomenon is quite alarming as exposure to excess levels of air pollutants, such as nitrogen dioxide and carbon monoxide, can cause a relapse in patients who had been recuperating from this debilitating disease.
It was noted that MS is triggered by inhaling gaseous particles which act as oxidizing agents and bring about neuroinflammation i.e., inflammation of the neurons.
As a result of this, immune cells attack the nervous tissue causing further degeneration and neuronal loss.
Multiple sclerosis can also be triggered by air pollution as pollutants cause neuroinflammation, which promotes the immune-mediated destruction of nerve cells.
Autism is a part of a group of neurodevelopmental abnormalities known as pervasive developmental disorders (PDD).
These disorders have three characteristic core deficits: diminished communication decreased reciprocal social interaction and stereotypical, repetitive patterns of behaviors or interests.
ASD is more frequent in boys with a male-to-female ratio of 4:1.
The prevalence of autism and its related disorders is on the rise across the globe. In the past few decades, it has alarmingly risen from 4 per 10000 to 6 per 1000 children.
The causal factor behind the development of autism and the other ASDs is still not clear.
However, it often occurs as a part of other conditions, such as fragile X syndrome, phenylketonuria, and rubella infections.
Various environmental factors such as toxic pollutants have also been implicated as potential causative agents in autism.
A 2018 study conducted by the Hebrew University of Jerusalem and Hadassah Ein Kerem studied the effects of traffic air pollution on children born between the years 2005-2009.
It was found that increased exposure to an environment with heightened levels of nitrogen dioxide lead to increased incidence of autism spectrum disorders in the children.
The risk was particularly elevated around 26 weeks after birth, particularly if the mothers were exposed to pollutants during the last trimester of their pregnancies.
The inhaled gaseous particles often affect the development of the brain and lead to increased risk of developing autism.
Inhalation of gaseous pollutants during pregnancy often results in neurodevelopmental deficits in the child leading to autism.
What can we Conclude?
To summarize, it can be said that air pollution causes several neurological problems.
It plays a major role in the development of Alzheimer’s as particulates stimulate oxidative nerve damage and cognitive impairments. Pollutants, such as PM2.5, also cause inflammation in the pre-frontal cortex leading to Parkinson’s.
Oxidative damage of the arteries and carotid arterial stenosis brought about by particulates increases the risk of ischemic stroke.
Neuroinflammation caused by agents like nitrogen dioxide and carbon monoxide cause the relapse of multiple sclerosis.
Finally, inhaling toxic pollutants during pregnancy enhances the risk of developmental problems like autism in the children.