Environmental Causes & Risk Factors Of Autism

Do you want to know what the most common environmental factors are that cause autism? Read on to find out.

steven zauderer
Steven Zauderer
September 20, 2023
min read

Overview Of Environmental Risk Factors For Autism

Autism is characterized by a set of impairments in communication, social development, and performing repetitive behaviors (stimming). Early theories focused on finding a single cause of autism. Some thought genetics were to blame, while others focused on finding a single environmental cause.

The problem with these theories that focused on finding a single cause of autism is that they seemed to explain some cases of autism, but not all of them.

You could find children who had autism but did not have the risk factor under study and vice versa. Now, we know that autism is the result of an interplay between genetics and environmental factors that can activate those genes.

Genetic factors are a factor in many cases of autism, but some children can develop autistic characteristics without the genetic components.

Recent statistics found that the prevalence of autism is nearly 1 out of every 59 individuals. Hundreds of genes have been implicated in the development of autistic traits.[1]

Some of the gene sequences associated with autism are inherited, while others appear to be spontaneous mutations. One of the challenges is that genes only account for 10-20% of the cases.[1] Two people with the same genetic factor for autism can have different levels of severity, and one might not have any significant autistic traits at all.

Despite the discovery of hundreds of gene sequences that were associated with autism, it seemed that this did not explain a majority of the cases.

It seemed as if just having the gene was not enough, but something had to turn it on. This is where the scientific branch called "epigenetics" comes into play.

Epigenetics is the study of how the environment works to "turn on" certain genes associated with conditions such as autism. It also studies how genes and environment play a role in other conditions, including heart disease, diabetes, and many others.

The field of epigenetics sheds new light on the complex causes of autism and how environmental factors can increase or lower a person's risk of being on the spectrum.

Environmental Risk Factor Qualifications

When many people think of an "environmental" risk factor, they think of pesticides, herbicides, and the many pollutants in the world around us.

From a research standpoint, anything that alters the risk of having a condition that is not encoded in the person's DNA is considered an environmental risk.

We are only beginning to understand what causes one of the many genes associated with autism to turn on.

Results of studies of environmental risk factors associated with autism have inconsistent results, at best.[2] It is now understood that certain environmental factors might place a person at greater risk of developing autism, but it is no guarantee. Just as with genetic factors, a person can be exposed to certain environmental risk factors and not develop autistic traits.

Established Environmental Risk Factors

Now, it is believed that environmental risk factors account for an increased risk of having a child with autism by up to 40-50%. Some risk factors associated with autism have more support than others do. A few of the ones that have a stronger correlation with autism include:

  • Premature birth
  • Birth close to an older sibling
  • Mother with diabetes
  • Children with older fathers
  • High blood pressure during pregnancy
  • Maternal use of certain drugs
  • Complications during pregnancy

Others factors correlated with autism include a bad case of influenza or hospitalization during pregnancy.[2] Autoimmune diseases and other immune responses also seem to play a role.[2] Taking certain medications, such as Valproate, during pregnancy also seem to increase the risk of autism.[2]

Maternal use of antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) has also been associated with increased autism rates.[2] It might also be noted that the psychological state of the mother during pregnancy can also affect the risk of autism, including feelings of isolation and a breakdown in relationships.[3]

It must be stressed that these factors do not mean your child will be born with autism, but they have shown a strong correlation in studies. The timing of environmental risk factors, the severity of the exposure, and the length of exposure all seem to affect whether an environmental factor will result in having an autistic child. Some of these factors can be reduced, while others cannot.

Other Factors Being Investigated

Other factors that are currently under investigation as potential contributing factors to autism include the quality of maternal interactions with the newborn, smoking and alcohol consumption, and obesity during pregnancy.[3] Post-birth nutritional factors are also under investigation, particularly the role of calcium and protein intake.[4]

Exposure to certain chemicals and substances during pregnancy and early childhood is also being investigated as a potential cause. These include inorganic mercury, heavy metals, and thimerosol used in vaccines. Other factors that are being investigated are exposure to hormone disruptors, such as polychlorinated biphenyls (PCBs) and phthalates.[4]

People with autism sometimes have problems with abnormal sleep patterns. Now, the role of melatonin and other neurotransmitters produced by the pineal gland is being studied as a potential factor.[5] Exposure to organophosphate pesticides, such as diazinon and chlorpyrifos, is another potential factor.[5]

One of the challenges of research into the causes of autism is that many of the factors associated with the development of autism also correlate with other conditions, such as birth complications. Also, it is difficult to find a study group that only has one risk factor. Many children with severe autism have been exposed to more than one risk factor, making isolating a single cause difficult.

Ruled Out Risk Factors

Autism was first identified by Leo Kanner in 1943. Kanner observed that many autistic children had highly intelligent parents and characterized them as not being "warm-hearted." This developed into what became known as the "Refrigerator Mother" theory and placed the blame on mothers who did not show adequate affection toward their children.

Fortunately, this theory was quickly abandoned and scientists began to focus on more plausible causes. Nearly 23 years later, the first epidemiological study found a prevalence of autism in 4.5 out of 10,000 people. It was then that serious research into environmental factors began.

Early studies led to a connection between certain vaccines and the development of autism. These vaccines included the influenza vaccine and those against whooping cough. These studies were found to be fraudulent, and no support has ever emerged to support these factors as a cause.[2]

Serious investigation into the role of genetics began to emerge in the mid-1980s. By the year 2000, the search for a single genetic factor was in full swing. This search for an "autism gene" resulted in many genetic factors being associated with autism, and the blame could not be placed on an "autism gene."

Environmental Factors that Lower the Risk of Autism

Just as some environmental factors have emerged that seem to raise the risk of having an autistic child, others have been found to reduce the risk. These include taking vitamin D and vitamin B-9 (folic acid). Zinc deficiency also correlates with the development of autism.[5]

What Should Parents and Prospective Parents Do?

Now, we know that it is unlikely we will ever isolate a single cause of autism, whether genetic or environmental. Many factors have a strong correlation with autism. The mechanisms of how these factors lead to the development of autism are not understood clearly.

What this means for parents and parents-to-be is that we need to focus on the things that can be controlled. One of the common themes found throughout the research is that the physical and emotional health of the mother plays a role in the development of autism.

Not all of the factors can be controlled, but it is important to work with your health professionals and identify risk factors that apply to you.

If you are pregnant, it is important to eat healthy foods, exercise, and avoid stress to the extent possible. The evidence is not definitive on the role of nutrition in autism, but what has been discovered so far makes a good case for taking prenatal vitamins.[2] Good prenatal care can help eliminate or reduce many environmental factors for autism.

Nothing can guarantee that you will not have a child with autism or predict that you will. If your child has autism, the best thing you can do is to work on building a good network of professionals and support. While it is tempting to try to "blame" something, spending time on this will not result in the best outcomes for your child or you.

Perhaps the most important advice is to make sure you have good information and try not to listen to the many myths out there about the causes of autism.

Take a common sense approach and use reliable sources for research, such as peer-reviewed journals. The best advice is to remember that we now know genes do not create your destiny, and staying healthy can help reduce your risk of your child developing autism or many other life-altering conditions.







steven zauderer

CEO of CrossRiverTherapy - a national ABA therapy company based in the USA.

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