Friday, March 31, 2023

Air Pollution: A mental health alert

A study has linked increased levels of NO2 in the air to au­tism and schizophrenia in children. UNICEF has estimated that air pollution is a major contributor to the an­nual deaths of six lakh children under five years globally.

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Today 92 percent of the world’s population lives in places where fine particulate matter (PM2.5) levels exceed WHO guidelines for healthy air. Air pollution and tobacco together are responsible for up to 20 million premature deaths each year. And outdoor air pollution, according to WHO, caused more than 4.2 million deaths globally in 2016. While in adults, higher air pollution levels are associated with increased cardiovascular and respiratory illnesses, a new study has found that in children, it could lead to schizophrenia.

The fallout of more pollution can be seen in various studies. For example, in a 2012 meta-analysis, published in the Journal of the American Medical Asso-ciat­ion (JAMA), short-term exposure to a variety of air pollutants (carbon mon-oxide, nitrogen dioxide and sulphur dioxide) was associated with an increased risk of heart attack—between 0.6 to 4.5 percent. In a study published in the New England Journal of Medicine, it was found that there was an increased mortality rate of 13 percent for every 10 mcg/m3 rise in PM2.5. Even a short-term increase in levels of particulate matter in air can be associated with a rise in mortality.

UNICEF has estimated that approximately 300 million children live in regions where air pollution exceeds standards by at least six-fold, and it is the major contributor to the deaths of six lakh children under the age of five annually. Therefore, improved air quality can benefit all children, not only those with lung disease.

As if physical health was not enough reason to improve air quality, now a study published in JAMA has shown that children who grow up in areas with heavy air pollution are at greater risk of getting mental illnesses too. The study assessed genetic data from iPSYCH—a project to find the basis and treatment of the most common and serious mental illnesses, including autism, bipolar disorder and depression. The researchers, including those from Aarhus University in Denmark, combined the iPSYCH data with information on air pollution from the country’s Department of Environ­mental Science. According to the study, children who are exposed to a high level of air pollution while growing up have an increased risk of developing schizophrenia. For each 10 mcg per cubic metre (g/m3) increase in the daily average of air pollution, the risk of schizophrenia increased by a fifth. Children who are exposed to an average daily level above 25 g/m3 have an approximately 60 percent greater risk of developing schizophrenia compared to those who are exposed to less than 10 g/m3, the UN requirement for air pollution levels.

Air pollution is also associated with an adverse effect on infant brain development, lung development and function (including asthma), and mortality rates of children. The researchers said the lifetime risk of developing schizophrenia is approximately two percent in people, but for those exposed to the highest level of air pollution, it is three percent.

And it was nitrogen dioxide (NO2), a key component of air pollution and smog, that was primarily responsible for it. NO2 forms when fossil fuels such as coal, oil, gas or diesel are burnt at high temperatures. This and other nitrogen oxides in outdoor air contribute to particle pollution and to chemical reactions that make ozone. It is one of six widespread air pollutants that have national air quality standards to limit them in outdoor air. NO2 can also form indoors when fossil fuels like wood or natural gas are burned.

A study published last year in JAMA Psychiatry showed psychotic experiences were significantly more common among adolescents with the highest exposure to NO2, nitrogen oxides (NOx) and PM2.5, even after adjusting for known risk factors for psychosis. NO2 and NOx together accounted for 60 percent of the association between living in an ur­ban setting and experiencing psychosis during adolescence.

Schizophrenia, incidentally, is a syndrome consisting of symptoms of psychosis that impact development and cognitive functioning. This includes hallucinations or delusions and disorganised speech. It can lead to impairments in cognition, including attention, memory and executive functions.

A diagnosis of schizophrenia is based on the presence of such symptoms, coupled with social or occupational dysfunction, for at least six months in the absence of another diagnosis that would better account for the presentation. Childhood schizophrenia starts prior to the age of 13. Thirty to 50 percent of patients diagnosed with childhood-onset schizophrenia had premorbid features of autism.

The risk of developing schizophrenia is also higher if you have a higher genetic liability for the disease. According to an article in the December issue of the Quarterly Review of Biology, our genes have evolved significantly since our an-ces­tors moved out of the forests. One of them is MARCO which provides the blueprint for production of a molecular hook used by immune cells in our lungs. The cells use this hook to clear away bacteria and particles, including silica dust. The human version of the MARCO gene is distinctively different from that of apes.

Gary Perdew, a molecular toxicologist at Penn State University, and his colleagues found evidence of smoke-driven evolution in another gene, AHR. This gene makes a protein found in cells in the gut, lungs and skin. When toxins get snagged to the protein, cells release enzymes that break down the poisons. Compared to other species, the human version produces a weaker response to toxins, perhaps because AHR protein is not the perfect protector—the fragments it leaves behind can cause tissue damage.

A child’s physiology and behaviour put him at an increased risk for many toxins. Attention concerning environmental exposure for children previously centred around lead and second-hand cigarette smoke. But now there is in-creasing awareness about the potential health effects of other exposure, including chemical allergens and irritants (formaldehyde resins), indoor and outdoor air pollutants, pesticides and other toxins.

In India, it’s time to file cases against the government for not being able to give us a clean environment. Living in an air pollution-free environment is our fundamental right under Article 21.

—The writer is President, Confederation of Medical Associations of Asia and Oceania, and Heart Care Foundation of India

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