Environmental influences may be risk factors for autism. Research into this area is ongoing, and no true consensus exists.

There is no known cause of autism. Researchers believe that there is a significant genetic component to the disorder, but many other factors, such as environmental exposure, have been shown in studies to contribute to autism spectrum disorder.

What Are Environmental Factors?

STAT News explains that in autism diagnoses and therapy, the term environmental factors is often used incorrectly.

In a colloquial sense, environment can refer to natural settings and the contamination thereof by pollutants, which is itself a factor in the development of autism spectrum disorder (ASD). However, scientists and doctors use the term environmental factor to mean anything that produces a biological or behavioral response that cannot be strictly attributed to genetic factors (that is, it is not already present in a person’s DNA).

In this context, environmental factors can mean anything — from food and drink, to air quality, to anything that comes in contact with the skin — that causes a biological or behavioral response. 

The Language of Epidemiology

Similarly, the terms risk and cause are frequently misunderstood. A cause is a catalyst that leads to the development of a disease or a condition. Risk factors, on the other hand, are elements that act together that increase the possibility that a disease or condition will develop.

In epidemiology, researchers have put down very specific criteria to establish whether something is a cause, a risk factor, or neither. When it comes to environmental factors causing autism, no one environmental factor has satisfied the criteria for causing autism. This has led researchers to conclude that environmental factors have to work in tandem, having some interaction with genetic factors, to lead to the development of autism. 

Environmental Factors & Autism

Many environmental factors have been linked to the likelihood that a child will be diagnosed with autism. Among them:

  • Older age of the mother or the father at the time of birth is a risk factor, according to the Acta Psychiatrica Scandinavica journal.
  • Having one autistic child increases the risk that a second child will also have the disability, but the exact degree of risk is not clear, writes JAMA Pediatrics.
  • Increased levels of air pollution during pregnancy (PLOS ONE), in combination with genetic factors (Epidemiology), is a potential risk factor.
  • The Developmental Neurobiology journal wrote that extreme illness or infection during pregnancy, such as those caused by reactions to bacterial or viral infections, can be an environmental factor in the development of autism. Vaccinations can prevent some of these infections, writes Frontiers in Human Neuroscience
  • Other environmental factors that could be at play include obesity during pregnancy, premature birth or the child having low weight at birth, and other complications. The Journal of Psychiatric Research suggests that interactions with certain genes can elevate the risks for delayed neurological development.

The Annual Review of Public Health notes that if a child is exposed to any one of these (or other) environmental risk factors in utero, it increases the chances of developing autism as much as four times the baseline rate.

Environmental Factors & Genetics

Autism develops as the result of a complex interaction between any number of genetic and environmental factors. More than a dozen genes have been identified as having a part to play in the development of autism spectrum disorder, but the full scope of the environmental factors remains elusive.

Why are the environmental factors for autism so difficult to pin down? One reason is that all the studies that have looked at the environmental factors are affected by so-called confounding factors, variables that make it difficult to isolate causal relationships between those factors and the development of autism.

For example, some research (like this from the BMJ journal) has indicated that a mother who takes antidepressants during pregnancy might put her offspring at “increased risk” for developing autism spectrum disorder. Other research (like this study published in Clinical Epidemiology) found “no significant association between prenatal exposure to antidepressant medication and autism spectrum disorders in the offspring.”

Still with medications, some research has connected in vitro exposure to valproate, which is used to treat epilepsy and bipolar disorder, to an increased risk of autism as well as other birth defects. This has led to some countries, like France, banning the prescription of certain forms of valproate to pregnant women or women who want to become pregnant.

As a result, research that has examined the role of environmental factors in the development of autism spectrum disorder do not demonstrate cause and effect.

Challenges of Measuring Environmental Factors

Additionally, even the established relationships between environmental factors and autism remain unclear. While children who have older fathers are more likely to develop autism than children who have younger fathers, it is unknown whether it is the advanced paternal age itself that leads to the increased risk.

It is also difficult to track or measure environmental factors. Parents might forget what they were exposed to, or they might not even be aware of key elements in their environment. On the other side of the scale, parents might attribute their child’s autism to an environmental factor that has nothing to do with it.

Parental, Prenatal & Perinatal Factors

Some environmental risk factors for autism are well established. The most well-known of these are correlated to gestation or birth.

The Autism journal noted that abnormal bleeding during pregnancy or high blood pressure can increase the risk of autism. Other related factors can include complications arising from cesarean delivery or preterm birth. Maternal diabetes has also been associated with autistic symptoms, according to the Pediatrics journal.

Although these factors are well documented, the mechanisms behind these connections are still not fully understood.

Researchers have looked at the immune system of expectant mothers to determine the risk of autism. Serious illnesses and infections (specifically bacterial infections, says the Journal of Autism and Developmental Disorders) have been implicated in an increased risk of autism in offspring. “Several maternal autoimmune disorders were correlated with autism,” adds the Epidemiology journal.

There is abundant evidence that exposure to air pollution during gestation, the third trimester, or early in the child’s life can significantly increase their risk of developing autism. However, air pollution has many components, and it is not fully known which of those components has a role to play in the development of autism.

A number of suspected risk factors have been ruled out. While there are connections between maternal immune conditions and autism, standard vaccinations administered during pregnancy, like those for influenza and whooping cough, do not increase the risk of autism.

Vaccines & Smoking as Factors

Similarly, childhood vaccinations also do not cause autism. The research that claimed to show a causal link between the two was fraudulent and later retracted. Despite many claims to the contrary over social media and from dubious channels, there is no credible research that supports a connection.

Smoking during pregnancy was once thought to contribute to the risk of autism. While smoking is itself generally unhealthy (and can cause other birth defects, like some forms of delayed development), the Pediatric and Perinatal Epidemiology journal writes on the topic of smoking during pregnancy, that “no associations were observed for childhood autism and Asperger’s syndrome.”

What should parents, prospective parents and caregivers do about environmental factors that can lead to autism? When a high risk for autism has been established, families should consult with a doctor, a pediatrician, or even a genetic counselor for recommendations.

In most cases, following general recommendations of staying healthy and getting vaccinations (for the mother) will be helpful to control that risk.

The Vaccine Controversy

Are vaccines one of the environmental causes for autism? The answer is a clear no, but despite overwhelming evidence, the controversy continues.

The myth comes from 1998, when an accredited British gastroenterologist named Andrew Wakefield tested 12 children, some of whom had autism spectrum disorders, others who didn’t. A report based on his study (published in The Lancet) found a possible link between the measles virus and autism.

The report claimed that the measles-mumps-rubella (MMR) vaccine resulted in everything from tissue damage to a weakening of the immune system. “Many children seem to develop autism” after receiving the vaccine, Wakefield and his team noted.

Children with autism often present with gastrointestinal problems. Wakefield theorized that the MMR vaccine released toxins from the intestines into the bloodstream, which would then travel to the brain.

The report itself made no mention of a causal connection between vaccination and autism, but Wakefield made public statements wherein he called for the suspension of the vaccine. These statements were what fueled the hysteria surrounding vaccinations, which Wakefield called a “moral issue.”

In 2000, Wakefield repeated these claims on American television, claiming vaccinations were behind what he called “an epidemic of autism.” This ignited what had been a fringe anti-vaccination movement in the United States, giving it mainstream attention.

Fatal Flaws & Conflicts of Interest

In 2004, British journalists discovered that Wakefield had a conflict of interest when he worked on his study for The Lancet, receiving over £400,000, which he had not disclosed. The UK General Medical Council  investigated and charged Wakefield with dishonest and professional misconduct.

The day before this news broke, the editor of The Lancet released a statement that called Wakefield’s research “fatally flawed,” and said that the conflict of interest, had it been known, would have led to the report being rejected.

Ten of the 12 co-authors of the paper withdrew their names from the article. Explaining their retraction, they clarified that although the paper did not establish any causal link between the vaccine and autism (because the data was insufficient), the “major implications for public health” were enough for them to disavow the original interpretation of the study’s results that The Lancet had published.

Further investigations revealed that Wakefield had applied for a patent on a “single-jab measles vaccine before his campaign against the MMR vaccine.” Additionally, contrary to what he wrote in the Lancet, the first page of Wakefield’s application for the patent explicitly claimed that the MMR vaccine “results in […] pervasive developmental disorder including autism in some infants.”

Wakefield denied any wrongdoing and claimed to be the victim of mistreatment from the medical and scientific communities. In 2010, the General Medical Council found him guilty of all charges of professional misconduct, accused him of acting with “callous disregard” for the well-being of the children in his study, and of “[bringing] the medical profession into disrepute.”

He was removed from the United Kingdom’s medical register, which is the most serious penalty the council could impose. The move ended Wakefield’s ability to legally practice medicine in the country. That same year, The Lancet officially retracted Wakefield’s original article.

‘This Damaging Vaccine Scare’

In 2011, the BMJ journal published an article where it reported gross inconsistencies in Wakefield’s Lancet article, including that the parents of the 12 children in the study were recruited by people campaigning against the MMR vaccine. The editors of the BMJ wrote that Wakefield was neither incompetent nor mistaken, but “a fraud.”

“Clear evidence of falsification of this data,” they wrote, “should now close the door on this damaging vaccine scare.”

However, the belief that there is a link between autism and vaccines persists. In 2009, the U.S Court of Federal Claims ruled in three test cases that “vaccines do not cause autism,” specifically shooting down any claimed link between the MMR vaccine and autism spectrum disorder. Yet, as Discover Magazine noted over a decade ago, “these rulings have done little to quell the angry debate.”

The myth continues to be spread by celebrities and politicians, on social media, and by conspiracy theorists and bad faith actors. There has been repeated rejection by doctors and researchers, but in spite of that — perhaps even because of it — a movement for vaccine skeptics has arisen. Outbreaks of measles have occurred in the United States, in Australia, and across Europe, driven primarily by a fear of vaccines and parents refusing to allow their children to be vaccinated.

The problem has escalated to the point where a number of European countries have made child vaccinations mandatory and imposed fines on parents who do not vaccinate their children.

In 2019, the World Health Organization classified the vaccine skepticism (also known as vaccine hesitancy) as one of the major threats to global health.

The Cost of Vaccine Skepticism

Discover suggested that the emotional toll that autism can take on a family has led well-meaning people to desperately look for causes or solutions. Even as the rate of autism diagnoses increases, the origins and mechanisms of autism itself remain elusive. The Annual Review of Public Health calls autism spectrum disorders “complex, lifelong, neurodevelopmental conditions of largely unknown cause.”

With this in mind, Discover suggests that it is not surprising that desperate parents and caregivers could latch onto Andrew Wakefied’s discredited theories, notwithstanding the medical support of vaccines.

The effects of this can be deadly. As recently as February 2020, a 4-year-old boy died from the flu in Colorado after his mother was advised by an anti-vax Facebook group (with over 178,000 members) to give her son vitamins, botanicals, fruits and vegetables, and not the prescription Tamiflu from the child’s doctor. As the boy’s condition worsened, one member of the group told the mother to “boil thyme on the stove.” 

The thread was removed from the Facebook group after news of the boy’s death broke. The owner of the group blamed the hospital for “[never] offering any real treatments.”

To this day, Andrew Wakefield continues to campaign against the use of vaccines, maintaining the validity of his research and conclusions.

Ongoing Research

While it is clear that vaccines are not a cause of autism, other environmental factors could potentially contribute to the onset of the disorder, such as exposure to toxins.

This is a critical area of autism research. Studies are ongoing to identify environmental risk factors and how these tie into genetic risk for autism.

In the coming years, we will hopefully learn more about how environmental factors play into autism. This research could then aid prevention, intervention, and treatment efforts.