Dr. Martin Myers, director of the National Network for Immunization Information and a pediatrics professor at the University of Texas at Galveston, explains that “This myth was originally created by a couple of mothers of autistic children who read about methyl mercury poisoning and thought it sounded like autism.”

Methyl mercury is different from ethyl mercury, or thimerosal, which, until 2002, had been used to preserve vaccines.  Today, the only common immunizations that contain thimerosal are Fluzone and Fluvirin, which also come in versions without thimerosal.

Thimerosal has been replaced by alternative preservatives; single-dose vaccines are also used, eliminating the need for preservatives.  One version of the diphtheria-pertussis-tetanus (DPT) vaccine has a trace of thimerosal.

Although myths to the contrary persist, no evidence has been found that links ethyl mercury in vaccines to autism.

Research conducted by the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health in Baltimore shows that thimerosal is excreted from children’s bodies far faster than is methyl mercury.  Dr. Neal Halsey, director of the Institute, states that the investigation of thimerosal in vaccines in 1990s came about not because of a concern about autism, but the concern that, “if by chance children got multiple thimerosal-containing vaccines, they might have enough mercury exposure that it might exceed the EPA guidelines.”

Dr. Halsey explains that the association between vaccines and autism, while incorrect, is understandable because symptoms may begin around the time of vaccinations.

Halsey states that organizations such as Autism Speaks are “not explaining that there will be coincidental timing of people recognizing the early signs of autism at the same time vaccines are given, so it’s an impossible task to try to keep doing research that addresses concerns that parents raise about bad things that are temporally associated with autism.”

The bottom line is that, while methyl mercury (such as that found in some fish and in now-recalled antiseptics Mercurochrome and Merthiolate) may cause problems in children in high doses, there is no causal connection between vaccines and autism.

For more information, see this article from the Pittsburgh Post-Gazette. Find mercury content of vaccines here.

According to Maureen Swanson, MPA, the director of the Healthy Children Project at the Learning Disabilities Association of America, “Researchers are finding harmful effects at lower and lower levels of exposure. They’re now telling us that they don’t know if there’s a level of mercury that’s safe.”

Evidence suggests a clear connection between toxins and children’s school performance.  Lead poisoning, for instance, lowers IQ and shortens attention spans.  While it is unknown exactly what the impact of many toxins may have on children’s developing neurological systems, groups such as the Autism Society of America, the Learning Disabilities Association of America, and the American Association on Intellectual and Developmental Disabilities (formerly the American Association on Mental Retardation) have teamed with dozens of other organizations to form the Learning and Developmental Disabilities Initiative, whose goal is to protect children from pollutants that can adversely affect brain development.

Chemicals used in pesticides, particularly a class called organophosphates, have been associated with hormonal disruption and cancer.  Although Dursban, the brand name of a chemical pesticide used on school grounds, has been banned in the United States, it may still be present in the environment.  Other now-banned chemicals such as organochlorines, found as recently as 2003 in head lice medication and dioxin, found in pesticides, and other chemicals may still be entering the environment and causing problems for children.

Polychlorinated biphenyls (PCBs), some of which are a form of dioxin, have been banned in the United States for years.  However, they are still found in the environment. Research has found that low-level exposure to PCBs in utero leads to poor reading comprehension, memory problems, and low IQ in children.

Flame retardants and plasticizers, such as bisphenol A (found in dental sealants, pacifiers, and baby bottles) cause health problems for children as well.  According to Elise Miller, MEd, executive director of the nonprofit Institute for Children’s Environmental Health and national coordinator of the Learning and Developmental Disabilities Initiative, “We all have bisphenol A in our bodies now.”  Bisphenol A can affect both the neurological and reproductive systems and appears to accumulate more around the fetus than in the mother’s blood.
Miller states that “Of the tens of thousands of chemicals that have been introduced into the environment in the last half-century, most have not been tested for human health problems—and only 15 have been thoroughly tested for neurotoxicity.” There is much debate among researchers as to how these chemicals affect children, and there has not been much research on the effects of how these chemicals might act in combination with one another.

However, as Miller states, “We all have hundreds of chemicals in our bodies today that didn’t exist a few decades ago. And we’re seeing increases in learning and developmental disabilities as well as many other chronic diseases. Currently, one in six children under the age of 18 have [sic] some kind of learning, or developmental, or behavioral disorder.”

Debate swirls around whether the increase in children affected is an actual increase and how much is due to factors like more accurate diagnoses, but Miller states that people who have worked with children for years are seeing an increase in the numbers of those affected by learning disabilities or behavioral issues.

Although the research may not be clear on many points, one thing is certain:  toxins in the environment affect children more than adults.  For instance, in a home with radon, an adult’s exposure level is half that of a 6-month-old.  Children have a higher metabolic rate and consume more fluids, food, and air than adults do, and spend far more time on the floor and in the dirt than children do.

Because children are still growing, their systems are more vulnerable than adults’ systems are.  Baby food and school busses have been found to contain pesticides and high levels of diesel exhaust respectively.  Children also put non-food items into their mouths, increasing their exposure to toxins.

Efforts to reduce lead exposure have been successful; in 1971, the government banned lead paint, and later, lead in gasoline and food cans, significantly reducing exposure.

However, lead has accumulated in soil and there are still lead paints in older housing.  Questions about potential lead paint exposure are standard in pediatricians’ offices, and in New York State, every child must be tested for lead at ages 1 and 2.

Research into autism and environmental exposure is ongoing.  An emerging area of research is studying whether there is a confluence of genetics and exposure that triggers autism. Swanson states that “We know autism has a strong genetic component [to autism], but researchers are now studying whether the increase in autism rates might be linked to a combination of genetic susceptibility and environmental factors. Several major research centers are looking into this, and study results already suggest it’s not just environmental factors and it’s not just genetics—it’s probably a nexus of both.”

Read more about environmental toxins and child development from Social Work Today here.

Vaccinations have been modified in light of increasing autism diagnoses. Mercury in vaccines was thought to trigger autism, but Dr. Karp states that, while 95 % of mercury was removed from vaccines in 2002, autism rates have continued to rise.  Similarly, a popular idea was that the measles, mumps, and German measles (MMR) shot caused autism, but recent Dutch and Japanese studies have found no differences in autism risk for those children who did and did not receive the immunization.

There is no clinical evidence linking autism and vaccinations. Dr. Karp states that, in light of these “dozens of studies examining over a million children [that have] failed to find any credible association between shots and autism,” he knows of “no plausible pathophysiologic pathway to link vaccines to autism.”

Regarding the rise in incidence of autism, Karp argues for promotion of childhood disease registries that will help to determine the true incidence of autism.  Changes in how delays are labeled may make it appear that more children are being diagnosed with autism, but a recent California Department of Heath study has provided evidence for an actual rise in incidence.

Karp states as well that “The National Children’s Study will establish over 100 study centers across the United States to test the blood of 100,000 newborns for scores of synthetic chemicals,” which may shed some light on causes of autism.

The Autism Society reports that “it is generally accepted that [autism] is caused by abnormalities in brain structure or function.”  Brain scans of children with autism show differences in the shape and structure of the brain as compared to normally developing children.  So is there a genetic component to these differences in brain shape and structure?

Some families have a pattern of autism, and some children, it appears, are born with susceptibility toward the disorder.  Research is being conducted on whether some genes may interfere with brain development that results in autism.

In 2007, Autism Speaks published preliminary results from the largest-ever genome scan that indicated that there may be a link between genetics and autism.  The study focused on a specific group of neurons called glutamate neurons and the genes that affect their development and function.  The findings suggested that these neurons have a crucial role in ASDs.

Autism Speaks chief scientist Andy Shih stated that “By combining cutting edge CNV analysis with the more traditional linkage and association [analyses], the scientists now have a promising new experimental framework to look for autism susceptibility genes.”  Shih went on to state that the “findings from the AGP linkage scan confirm the value and contribution of multidisciplinary collaboration to advancing autism research.”
The identification, then, of these genes may provide insight into the causes of autism, in turn providing new ways of diagnosis and treatment for those affected by it.

While pin-pointing a specific gene that causes autism may be a long way off – if it is ever located – any ongoing research that will help identify autism’s underlying causes will ultimately result in more effective treatments and interventions.

A medical test for autism still does not exist, and diagnosis is made based on observation of symptoms.  While research on a genetic link to autism is promising in terms of diagnosis and treatment, the ability to determine a genetic link to autism in utero brings with it its own set of moral and ethical debates.

To read more about the autism genome project click here.

Regardless of the cause in the increase in diagnoses, there is no medical test that can rule out ASD nor has one single cause been identified.  No cure is available, but effective treatments and interventions exist.

Many theories as to causation exist as well, however, including genetics, the environment, and the role of thimerosal, a preservative formerly used in childhood vaccines, particularly the measles-mumps-rubella (MMR) vaccine. (Thimerosal has not been routinely used as a preservative since 2001).

Any quick Internet search of autism will bring up results that point to a connection between autism and vaccines, as well as a number of results that dispel a connection between the two.  With so much information available, and some of it from seemingly credible sources, it may be difficult for parents to determine what is fact and what is fiction.

While it is true that individuals with autism may have difficultly metabolizing heavy metals and other environmental toxins, no link has been found between vaccines and autism.

The Centers for Disease Control and Prevention states that “evidence from several studies examining trends in vaccine use and changes in autism frequency does not support such an association.”  The CDC goes on to state that a scientific review by the Institute of Medicine (IOM) concluded that “the evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism.”

The CDC supports the conclusion reached by the Institute of Medicine, and the prevailing belief among autism experts is that not only is there no correlation between vaccines and autism, but that not vaccinating children against preventable childhood diseases is dangerous.

Furthermore, it is important for parents to remember that vaccines undergo extensive testing by the Federal Drug Administration before being approved for use and continue to undergo review and testing while in use.

While parents are justifiably concerned about preventing autism, the lack of a causal connection between childhood vaccines and autism should ease their minds.  Research continues and discoveries are being made daily as to the causes of this complex disorder, but parents should heed the advice of the American Academy of Pediatrics and the CDC and be sure their children obtain vaccines against preventable childhood diseases.

Heavy metals such as mercury are more prevalent in our environment today than they have been in the past.  Individuals who have ASD or are at risk for developing it have a decreased ability to detoxify and metabolize these toxins.

Not only are heavy metals more prevalent; the incidence of autism is on the rise as well.  University of California-Davis researchers have reported that the incidence of autism has risen in California from 205 in 1990 to more than 3000 in 2006.  Over the past 15 years, nationwide autism diagnosis rates have also risen dramatically.  This increase has led researchers to “start looking for the environmental culprits responsible for the remarkable increase in the rate of autism in California,” according to Irva Hertz-Picciotto, epidemiology professor at University of California-Davis, who led the study.

Many researchers believe there may be a connection between a pregnant woman’s exposure to chemical pollutants, metals and pesticides in particular, and the alteration of a developing baby’s brain structure that triggers autism.

Chemicals in the environment that alter how the brain grows include mercury, polychlorinated biphenyls (PCBs), bromated flame retardants, pesticides, and lead.  Exposure to PCBs has decreased in recent decades, but exposure to other chemicals such as insecticides and flame retardants has risen.

One study has found that mothers of children with ASDs were twice as likely to use pesticide-containing pet flea shampoos; another study has found a link between compounds used in vinyl and cosmetics and an increase in autism.  Hertz-Picciotto reports that products like antibacterial soaps can change immune systems and therefore harm to brain.

Also potentially altering the immune system could be a new infectious microbe (a virus or bacterium) to which infants and fetuses might be exposed.  Autism rates in the 1970s increased due to the rubella virus.

In short, according to Hertz-Picciotto, causes of autism could be “in the microbial world and in the chemical world.”

Research regarding the link between vaccines and autism, however, has not been proven by research.  The Centers for Disease Control and Prevention has conducted numerous studies on the safety of vaccines and the link between thimerosol, a preservative used in vaccines.  The studies have found the there is no association between autism and vaccines.

Read more about the UC Davis study here.