The environment as a risk factor for developing autism or ADHD

Brain development is the process through which neurons form and mature, and it is divided into six stages: proliferation, migration, differentiation, synaptogenesis (the formation of synapses, the connections between neurons), myelination, and apoptosis. This process begins during pregnancy and continues until the end of adolescence.

Exposure to environmental factors during this period can lead to altered brain development and affect cognition , such as: decreasing IQ, or increasing the risk of developing different disorders such as autism or attention deficit hyperactivity disorder (ADHD).

Air pollution

Several studies have observed an association between exposure to certain concentrations of particulate matter (PM2.5) and a diagnosis of autism. Connections have also been found between exposure during pregnancy and throughout childhood and a decline in cognitive function (related to IQ, which is an individual's ability to process information) and neurobehavioral problems. Specifically, childhood exposure has shown that children attending schools with high levels of traffic-related pollution exhibited slower cognitive development over the course of a year, as well as other cognitive impairments related to pollution received during their commute to and from school, or short-term attention spans (within the last 24 hours).

Finally, since specific effects have been observed in certain areas of the brain, it is believed that these could help explain the reason for the cognitive effects observed.

Detection and diagnosis of autism spectrum disorder

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Metals

In this section, it is important to note that lead, methylmercury, and arsenic are recognized neurotoxic compounds, and therefore, have been found to severely disrupt the nervous system and cause brain damage. Findings regarding the impact of low concentrations of methylmercury during pregnancy have been highly controversial, as cognitive and neuropsychological effects have been observed in some cases, while no associations have been found in others. This may be because fish, the main source of methylmercury, also contains essential fats that are beneficial for brain development. Regarding neurobehavior, prenatal and childhood mercury exposure is associated with autism and ADHD.

In the study of the effects of lead, there is more variety, and it is difficult to distinguish whether the impact stems from prenatal exposure or exposure during the first years of life. There is a much larger body of research studying childhood exposure, showing a link to cognitive function, the risk of ADHD, and other behavioral problems in adulthood.

Regarding cadmium, there is evidence of its impact on cognitive development and behavioral disorders, but few studies regarding ADHD.

Finally, arsenic exposure has been associated with a decrease in IQ, impaired cognitive development, and some neurobehavioral disorders. Interestingly, one intervention study observed that reducing arsenic concentrations in the drinking water of a group of children led to an improvement in a type of memory called working memory.

Persistent organic pollutants

In 2015, a review was published that compiled the evidence from the last ten years on the association between exposure during pregnancy and the first years of life to PCBs and alterations in neuronal development and behavioral disorders.

Pesticides

Regarding neurodevelopment, exposure to pesticides is one of the exposures with the most evidence and of the highest quality, since it is known that some of the components of pesticides are neurotoxic, that is, they have the ability to seriously alter the functions of the nervous system.

Prenatal exposure has been linked to reduced IQ scores and other measures of mental and psychomotor development in children. Regarding exposure during the first years of life, there are few studies, and many of them present inconsistent results.

Chemicals present in personal hygiene products and plastics

As previously mentioned, phthalates and BPA are among the chemicals found in personal hygiene products and plastics. Studies on phthalate exposure during pregnancy have shown that exposed children may exhibit reduced psychomotor development, and those exposed during childhood may have a lower IQ. There are still uncertainties regarding the link between phthalates and the development of autism spectrum disorder. Regarding BPA, there are inconsistencies about the impact of exposure on neurons, whether biological sex plays a role, and whether prenatal or childhood exposure is the determining factor. Associations have been observed with executive or cognitive functions.

ADHD, a common disorder in the child population

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Noise

In the case of noise, most studies examine exposure during the first years of life and its relationship to neurodevelopment. The majority of evidence regarding this exposure establishes a link with long-term memory, reading comprehension, and behavioral disorders such as emotional distress or hyperactivity, although in some cases the evidence is inconsistent or insufficient.

Green spaces

Most studies have also assessed childhood exposure to green spaces and its impact on neurodevelopment. Exposure to these natural and/or green environments has been observed to have beneficial effects on children's attention span and cognition. However, these studies are very preliminary, and the evidence is limited, so further research is needed to clearly determine the beneficial effect of these environments.

This is an original article from the 1 3rd FAROS Report The environment and its impact on maternal and child health: what are we facing.