Here’s how air pollution harms our bodies

The days after Diwali are marked by uncontrolled levels of PM2.5 and 10 in the thick, rancid air over our cities. It’s time for a ready reckoner

Both short-term and long-term exposure to air pollution can lead to a host of diseases and even premature death. And it is not just sick persons, high pollution levels in the air can have adverse health impacts on healthy people too.

In India, air pollution was responsible for 1.67 million deaths in 2019(HT Photo/Raj K Raj)

The World Health Organisation (WHO) describes air pollution as the presence of one or more contaminants, or particulate matter (such as PM 2.5 or PM 10), in the atmosphere in the form of dust, fumes, gas, mist, odour, smoke or vapour, and in quantities and for durations that can be injurious to human health. The main pathway of exposure to air pollution is through the respiratory tract. Breathing in these pollutants leads to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout our body, impacting the lungs, heart, and brain among other organs and ultimately leading to disease. It also leads to death.

Pollution was responsible for nine million deaths in 2019 – equivalent to one in six deaths worldwide — according to a report published in The Lancet Planetary Health last year. It added that 75% of these were due to air pollution specifically. That’s 6.67 million people worldwide, dead due to air pollution (both household and ambient). Of them, 4.5 million died due to ambient (atmospheric) pollution, up by 300,000 since 2015 and by 1.3 million since 2000.

In India, air pollution was responsible for 1.67 million deaths in 2019 — 17.8% of all deaths in the country, the largest number of air-pollution-related deaths of any country in the world. The majority of these deaths, 980,000, were caused by ambient PM2.5 pollution. Another 610,000 were due to household air pollution, according to the report. The world’s highest ambient PM2.5 levels — on a population-weighted average — are seen in India.

“There is suggestive evidence also linking air pollution exposure with increased risk for adverse pregnancy outcomes (i.e. low-birth weight, small for gestational age), other cancers, diabetes, cognitive impairment and neurological diseases,” a WHO document on the health impact of air pollution reads.

Pollutants with the strongest evidence for public health concern include particulate matter (PM), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2) and sulphur dioxide (SO2). Fine particulate matter are especially important source of health risks, as these very small particles can penetrate deep into the lungs, enter the bloodstream, and travel to organs causing systemic damage to tissues and cells.

“When we say PM 2.5 or 10, it’s just the particle size that we are talking about and the kind of damage depends on what creates the particle such as firecrackers, fuel combustion, stubble burning etc. The particulate matter formed due to diesel or kerosene burning can even cause lung cancer,” said Dr GC Khilnani, former head of the pulmonology department, AIIMS, Delhi.

The damage starts with inflammation of the airway, and the finer the particulate matter, the deeper it penetrates. Young lungs are vulnerable as they breathe at twice the rate that adults, which makes them inhale larger amounts of harmful pollutants, and it does more damage to the lungs of children under eight years of age as their lungs are still developing.

“Ultrafine particles of 0.1 microns or less do maximum damage. These penetrate the lung and reach the bloodstream, and once in blood, these can reach anywhere — the brain, the heart, kidneys etc. Even perfectly healthy persons can experience short-term symptoms such as breathing issues, sore throat or red eyes,” he added.

What makes the condition worse is high moisture levels in the air combined with a drop in temperature around a particular time of the year when levels peak making it conducive for viruses and bacteria also to thrive in the atmosphere and making people prone to catching infections.

The WHO says nearly every organ in the body is impacted by air pollution. Due to their small size—respirable size— some air pollutants are able to penetrate into the bloodstream via the lungs and circulate throughout the entire body leading to systemic inflammation and carcinogenicity. Particulate matter (PM) of 2.5 and 10-micron size is considered respirable size and can travel down to the lowest part of the lung.

Exposure to high levels of particulate matter can lead to reduced lung function, respiratory infections and aggravated asthma from short-term exposure. Whereas long-term or chronic exposure to fine particulate matter increases a person’s risk for diseases with a longer onset, like some noncommunicable diseases including stroke, heart disease, chronic obstructive pulmonary disease and cancer.

The specific disease outcomes most strongly linked with exposure to air pollution include stroke, ischaemic heart disease, chronic obstructive pulmonary disease, lung cancer, pneumonia, and cataracts (household air pollution only).

Breathing in heavily polluted air can cause irreversible damage to the artery.

“When these fine particles that lungs aren’t able to filter reach the bloodstream, they get attached to the blood vessel walls, i.e. the arteries. Over a period of time, clots form inside the vessel and they lead to blockages. There’s a sudden narrowing of the blood vessels that can eventually lead to a heart attack,” said Dr Upendra Kaul, chairman, cardiology, Batra Hospital & Medical Research Centre.

This can lead to an unstable angina, which means that blood and oxygen flow to the heart is not enough, which causes a heart attack. In patients who already have blockages, exposure to pollutants tends to accelerate the process. Respiratory diseases can also cause damage to the heart.

“Chronic bronchitis also leads to heart disease though of a different kind. It’s called cor pulmonale, or enlargement of the heart,” added Dr Kaul.

What happens to the brain

The brain is also not spared from the adverse effects of pollution.

“When the heart malfunctions, it automatically also affects the brain functioning as blood or oxygen flow is restricted to the brain which can lead to stroke. Also, inhaling pollutants emits certain chemical responses within the body that can also cause stroke over a period of time,” said Dr Deepak Aggarwal, professor, neurosurgery, AIIMS.

Since pollutants affect a person’s immunity it can also cause autoimmune disorders.

“Exposure to pollutants can also lead to a condition called vasculitis, meaning inflammation of blood vessels that leads to thickening, weakening, narrowing or scarring of the vessels. This could also lead to stroke,” he added.

What happens to the mind

Recent studies have also shown the impact that air pollution can have on a person’s mental health.

Clara G Zundel, postdoctoral research fellow in psychiatry and behavioural neurosciences, Wayne State University, in a World Economic Forum report said, “People who breathe polluted air experience changes within the brain regions that control emotions, and as a result, they may be more likely to develop anxiety and depression than those who breathe cleaner air.”

A 2022 study conducted on a group of people from the United States and Denmark found that exposure to air pollution is significantly associated with an increased risk of psychiatric disorders including depression, schizophrenia, bipolar disorder and personality disorder.

Doctors said that prolonged exposure to such high levels of pollution raises mental health concerns and worsens symptoms among patients already diagnosed with such illnesses.

Dr Om Prakash, professor of psychiatry and deputy medical superintendent at the Institute of Human Behaviour and Allied Sciences (IHBAS), said that severely polluted days, as are frequently recorded in the national Capital during winter months, can force people to stay indoors for long durations, which can indirectly trigger feelings of anxiety, worthlessness and hopelessness even among healthy adults.

“During high pollution days, a lot of our daily activities are restricted, which includes something as basic as going for walks or going grocery shopping. While a day or two is fine, Delhi and the neighbouring towns often record extremely high pollution levels for days together and that can have an indirect impact on a person’s mental health,” Dr Prakash said.

He added that for people with preexisting conditions, pollution months can cause worsening of depression and anxiety symptoms. These months become critical for patients because there can be tendencies to skip medicines and routine doctor visits.