The global increase in air pollution represents an increasingly concerning environmental risk factor for neurodevelopmental disorders, particularly autism spectrum disorder (ASD). Recent epidemiological studies have revealed compelling associations between exposure to specific air pollutants, including fine particulate matter (PM), nitrogen oxides (NO, NO2), sulfur dioxide (SO2), and ozone (O3), and increased risk of ASD.
Autism spectrum disorder (ASD) is a complex condition that affects neurodevelopment, often manifesting as difficulties in communication, repetitive behaviors, and challenges in social interactions.
Although the exact cause of ASD is not yet fully understood, researchers know that it results from an interplay of genetic and environmental factors.
Recently, air pollution has emerged as a possible environmental risk factor that may play a significant role in the development of ASD.
Air pollution consists of small particles and toxic gases emitted by industries, vehicles, forest fires, and other human processes. Some of the most harmful components include fine particles called PM2.5 (smaller than 2.5 micrometers in diameter), nitrogen oxides (NOx), ozone and volatile organic compounds.
These substances are so small that they can be inhaled deep into the lungs and enter the bloodstream, spreading throughout the body.
Illustration of the link between air pollution and ASD. Source: Shashank Kumar Ojha and Haitham Amal
In recent years, scientific studies have suggested that exposure to air pollution, especially during pregnancy and early childhood, can have detrimental effects on the developing brain. The developing nervous system is extremely sensitive to chemicals, and exposure to toxins at the wrong time can alter critical processes, such as the formation of neural connections.
Research has shown a growing association between exposure to air pollution and an increased risk of ASD. Studies conducted around the world have looked at large populations and found that children exposed to high levels of pollutants during pregnancy or early childhood are more likely to be diagnosed with autism.
One proposed mechanism is inflammation: pollutants can cause inflammation in the mother’s body during pregnancy, affecting the intrauterine environment. This can alter the development of the baby’s brain. In addition, pollutants can cross the placenta, directly exposing the fetus to toxins that can interfere with the healthy growth of brain cells.
Another factor is oxidative stress. Air pollutants can trigger the production of free radicals, unstable molecules that damage cells and tissues. The brain, because it is highly dependent on oxygen, is especially vulnerable to this damage.
Epigenetic modifications and disruption of the glutamatergic/GABAergic neurotransmitter system have also been identified.
The timing of exposure appears to be crucial, with greater vulnerability during prenatal development and early childhood, when critical neurodevelopmental processes such as neuronal migration, synaptogenesis, and myelination occur.
But is it possible to avoid this risk? Although we cannot completely eliminate exposure to air pollution, some measures can reduce the risks. Pregnant women, for example, can avoid exercising outdoors on days of high pollution and use air purifiers at home.
Public policies aimed at reducing pollutant emissions, such as regulating industries and promoting the use of electric vehicles, are also essential to protect vulnerable populations.
Despite the evidence, scientists emphasize that the relationship between air pollution and ASD is still not fully understood. It is not a determining factor, but rather an additional risk.
Autism is a multifactorial disorder, and air pollution is just one piece of the puzzle, which includes genetic predisposition, other environmental factors, and complex interactions between these elements.
Future studies will continue to explore how different types of pollutants affect the developing brain and how we can mitigate these effects. This field of research is crucial to better understanding the causes of ASD and developing strategies to prevent new cases.
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Air pollution: an emerging risk factor for autism spectrum disorder
Shashank Kumar Ojha and Haitham Amal
Brain Medicine (2024), 1–4; Published online: 12 November 2024
Abstract:
The global surge in air pollution poses an increasingly concerning environmental risk factor for neurodevelopmental disorders, particularly autism spectrum disorder (ASD). Recent epidemiological studies have revealed compelling associations between exposure to specific air pollutants, including fine particulate matter (PM), nitrogen oxides (NO, NO2), sulfur dioxide (SO2) and ozone (O3), and increased ASD risk. While the rising global ASD prevalence, now affecting 1%–1.5% of the population, partially reflects expanded diagnostic criteria and enhanced screening, mounting evidence points to the critical role of gene–environment interactions in ASD etiology. Air pollutants can trigger multiple pathogenic mechanisms, including neuroinflammation, oxidative/nitrosative stress, epigenetic modifications, and glutamatergic/ GABAergic neurotransmitter system disruption. The timing of exposure appears crucial, with heightened vulnerability during prenatal development and early childhood when critical neurodevelopmental processes, such as neuronal migration, synaptogenesis, and myelination occur. Research priorities should focus on how air pollutants affect brain development in genetically susceptible individuals, especially during pregnancy and early childhood. Better ways are needed to identify individuals at the highest risk and develop practical protective measures. Given the rising global pollution levels, this knowledge will help shape meaningful public health policies to protect future generations from environmental factors that may contribute to ASD.
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