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Home » Glyphosate causes autism – another debunked vaccine myth

Glyphosate causes autism – another debunked vaccine myth

Another one of those pseudoscientific tropes from the anti-vaccine religion has reared its ugly Bigfoot head – glyphosate causes autism. And, of course, the anti-vaxxers believe that vaccines are filled with that nasty chemical, so by some weird transitive logic, they think that vaccines cause autism because of glyphosate.

Yeah, no.

Of course, the belief that “vaccines cause autism” has been thoroughly debunked by powerful, robust, repeated clinical and epidemiological studies. It is “settled science” (and read the link, so that you actually understand what is meant). Now we have the oft-repeated myth that glyphosate causes autism spectrum disorder (ASD). The evidence that supports that claim is fairly weak, possibly nonexistent.

Even if it did, and most scientists are highly skeptical of the claim, we still know that there is almost no glyphosate in vaccines. And once again, even if there were and even if glyphosate causes autism, we know that there is no link between vaccines and autism. None. 

A few years ago, Emily Willingham, Ph.D., whom I consider to be one of the leading ASD scientific experts on this planet, wrote a hysterical and scientifically skeptical article about all of the popular causes of ASD – Dr. Willingham noticed that there were new claims about what causes autism. Parents need to blame someone for their child’s neurodevelopment, so that’s how vaccines got into the crosshairs.

But let’s look at some of the science, and figure out if there’s any mechanism by which glyphosate causes autism.

All about autism 

I’m not going to give you a highly detailed dissertation on autism spectrum disorder (ASD), because it would go on for hundreds of thousands of words. ASD describes a range of conditions that are considered to be neurodevelopmental disorders. The official diagnosis and description has recently been revised and can be found in the fifth revision of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders 5th edition (DSM-5).

The DSM-5 redefined ASD to encompass the previous diagnoses of autism, Asperger syndrome, pervasive developmental disorder not otherwise specified (PDD-NOS), and childhood disintegrative disorder. These disorders are generally characterized by social deficits and communication difficulties, stereotyped or repetitive behaviors and interests, sensory issues, and in some cases, cognitive delays.

One of the enduring myths from some parents of autistic children is that their children are defective or inferior to others. There are even stories of parents and caregivers murdering autistic children – some people even excuse the murder because of the “difficulties” of raising an autistic child. 

But for most parents of children with ASD, they accept them with love. Autism can be treated and managed like other medical issues, and many of these children grow into adults with a high quality of life. No one claims it’s easy, but successful management and treatment of ASD have improved greatly over the years.

Causes of autism

Most real scientists accept that the likely cause of ASD is some combination of genetics and environment.  A recent study examined the causes of ASD, and researchers determined that about 81% of the cause is linked to genetics – that is, mutations from the parents are the main cause of ASD. There is also some evidence that prenatal complications may be related to ASD, but the data has not been widely accepted.

Yes, that means about 19% of the causes of ASD are related to environmental conditions.. Just so it’s clear to the reader, it does not mean if we removed genetics from the issue, then 19% of ASD cases are strictly related to the environment, like vaccines. What it does mean is that without the genetic predisposition, ASD may not arise. It’s complicated.

Despite what we know scientifically about autism, that hasn’t stopped people from claiming that vaccines, or GMO foods, or glyphosate are the “environmental trigger” which leads to autism. 

Photo by Kees Streefkerk on Unsplash.

Let’s talk about glyphosate

Again, I won’t try to bore you with a thousand pages about a chemical. 

Glyphosate (Bayer’s  Roundup and Ranger PRO) is a broad-spectrum systemic herbicide used to kill weeds, especially annual broadleaf weeds and grasses that are known to compete with commercial crops grown around the world.

It has several advantages over many herbicides in that it breaks down in the soil into non-toxic organic molecules, reducing or eliminating contamination of groundwater and lower soils. This is a large improvement over other types of herbicides. In other words, despite claims to the contrary, glyphosate does not remain in the environment for very long, generally between a few days to three months

Bayer (who acquired Monsanto but has deprecated the brand name) has developed genetically modified (GMO) corns that are resistant to glyphosate so that farms can apply the herbicide to kill the competitive weeds while not harming the crop. This allows farmers to suppress the weeds while allowing better production out of the grain crop. There is robust evidence that glyphosate has no effect on crop yield while reducing competing weeds at a lower cost than other modalities.

Whatever the benefits of glyphosate, GMOs and the herbicide are tied together in many minds – in fact, the anti-GMO forces are some of the most vehement pushers of the vaccine glyphosate causes autism trope. Additionally, there is a “chemophobia” amongst many people which target anything that doesn’t sound like it comes from mother nature (which produces literally trillions of chemicals, many of which are far more dangerous to humans than glyphosate).

Although some fear of “chemicals” can be justified, we need to remember a key point – the dose makes the poison In toxicology. There are doses of any “chemical” that can be safe or unsafe. Water, for example, can be toxic if consumed at certain doses – sure, the dose is high for water toxicity, but it exists at a level that might surprise you.

Of course, as a result of this chemophobia, and misinterpreted scientific research, there has been an ongoing effort by many people to claim that glyphosate causes cancer. This has led to a Monsanto bashing across the internet along with several lawsuits. There have been a few robust studies that dismiss any link between glyphosate and cancer in general.

Just to be clear, I am agnostic about Bayer (or Monsanto) – I only care about the published, robust, repeated scientific evidence whether glyphosate causes autism spectrum disorder.

The first glyphosate causes autism paper

Ignoring the horrible science pushed by people like the lunatic Stephanie Seneff, who has written papers that are published in low impact factor predatory (pay-for-play) journals, there are two reasonable studies that seem to point to a possible link between glyphosate and autism. But they’re both very weak studies. 

The first article, by Janie F Shelton, was published in the moderate impact factor journal, Environmental Health Perspectives. The authors attempted to outline an epidemiological correlation between agricultural pesticides (including glyphosate) and neurodevelopmental disorders.   

As I do with many studies that I analyze, I like to take a meta-view of the research. 

 The journal itself has an impact factor of 8.05, which is not low, but certainly is not in the upper tier of journals. In many academic environments, any article published in journals with an impact factor less than 10 may not merit consideration of tenure (although this guideline is not universally employed).

The authors of the article are mostly from the University of California-Davis, a top research university, which has a lot of focus in agricultural sciences. The first author is Janie F Shelton, who has published four articles about environmental pesticides and autism in which she was the primary author. That’s all she’s published so far.

In one of her previous articles, Dr. Shelton appeared to indicate that because mothers in the US have a higher burden of pesticides in the blood, there is some causal link with the higher rate of ASD in the USA. Amateur epidemiologists often make this mistake – look at one factor in a huge population, and assume that there is a causal link because you can show some spurious correlation.

The problem with this older study is that it probably cannot show even correlation, because population-level studies of ASD, which included a country as large as the USA, can be influenced by hundreds of known and unknown factors called confounders. Eyeballing numbers from a large population and trying to draw conclusions is almost impossible. You have to narrow your studies to levels where you can control for these confounders.

I wrote about this study in detail here – so I’m going to give you the 1000 meter view of Shelton’s research.

  1. Basically, this study is a case-control study, which is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case-control studies are extremely important in epidemiological research, but, in the hierarchy of evidence, it is of fairly moderate rank. Why? Because data from case-control studies tend to be observational rather than objective, like in double-blind clinical trials.
  2. Because California carefully tracks type, amount and date pesticide applications, the authors could examine how close the mothers of the subjects lived to where pesticides were applied. So, the authors could then find subjects who lived in areas that were relatively close to farms that had pesticides applied on a particular date.
  3. The study populations were: 486 with ASD, 168 with development delay (DD) and 316 neurotypical. Moreover, all of these study subjects were found in a small area within a two-hour drive of the University of California, Davis.

Let’s stick with my issue of confounding factors. The authors wrote:

Other potential confounders explored but found not to satisfy criteria for confounding based on inclusion in the DAG or the change in estimate criterion were: distance from a major freeway, maternal major metabolic disorders (diabetes, hypertension, and obesity), gestational age (days), latitude of residence, type of insurance used to pay for the delivery (public vs. private), maternal age, paternal age, and season of conception.

They seem to ignore all other environmental factors that would be important for this type of study. It’s possible that such a study would become complex, but that’s why it’s hard – so that we know the results will stand up to scrutiny and in-depth analysis. And that the data can be separated from other data so that we can have a reasonable conclusion.

Here are some other criticisms I have of Shelton’s study 

  • The study is missing evidence that the pesticides scattered beyond the target areas (according to wind patterns or whatever). Agricultural operations despise wasting pesticides and attempt to be accurate in the application. What convincing evidence did the authors present to make me, or any scientific reader, think that the pesticides actually landed near the subjects? That would be hardly any evidence at all. 
  • A study like this requires a fairly decent dose-response effect, one of the key factors in toxicology, to jump on board the glyphosate causes autism train. Or any pesticides causing autism train. 
  • The results were based on such small numbers, which left us with relative large statistical errors. If you looked at each result, it ranged from exposure reduced the risk of autism to exposure tripled the risk of autism. But in the end, given the size of the error, the increased risk seemed to be clinically small – you might think that a 58% increased risk is high, but with such small subject numbers and lack of analysis of confounding factors, it becomes difficult to determine if that 58% is important. In other words, the relative risk was so tiny that it could be overwhelmed by any of the ignored confounding factors.
  • The authors spent an inordinate amount of time discussing other animal studies, tying pesticides to neurodevelopmental disorders. Animal studies can be interesting but rarely do they lead to clinical importance. 
  • We have no evidence of blood levels of these pesticides in the mothers. Do we know if being closer to or farther from the site of the application had any influence over the blood level of the pesticide? We have no idea of whether these mothers actually absorbed enough pesticides to allow us to determine if we can actually show a correlation between these chemicals and ASD. 
  • Where is the causality? Even if this data made sense. Even if the size of the subject groups were 100X larger. Even if we could show blood levels. This study has done nothing to provide a physiologically plausible pathway between exposure and ASD, which would be the basis of causality. Now, if they did meet those conditions, I’d be substantially less skeptical of their conclusions.

The captivating Orac also did a review of this study, almost for the same reasons as I did – here comes ANOTHER cause of autism. His review of the data lead him to this observation:

The sine qua non of a good study demonstrating an association between an environmental exposure and a condition requires the actual verification and quantification of the environmental exposure under study in the cases. Sometimes this involves measuring the actual levels of the chemicals in question, either in the research subjects (ideally) to document exposure or in the places where they live and work.

In some respect, Shelton and her co-researchers took the lazy way for this study. It’s almost like what the so-called “vaccine researchers” do – they sat in front of a computer, dug up the California database for pesticide application, then look at ASD diagnoses in the same geographic area, then said, “voila, we have a correlation.”

The second glyphosate causes autism paper

In a study by Ondine S von Ehrenstein, from the University of California at Los Angeles, and published in BMJ, the authors used the same database used by Janie Shelton to examine which pesticides increased the risk ASD. They specifically examined whether glyphosate causes autism.

And they found that there is a 33% higher risk of ASD in areas with glyphosate applications. But just like the Shelton paper, there are still major issues:

  1. There appeared to be no discussion of confounders. For example, one could argue that individuals who live near farms where glyphosate is applied have different healthcare, or different nutrition, or different anything. Those factors must be a part of the statistical analysis of any decent epidemiological.
  2. Once again, we have no data on actual exposure, like blood levels.
  3. It’s population-level data again – there is no drill down to the individual.

I don’t get these type of studies. They work to scare us without giving us actual useful data to determine if we really should be scared.

To be fair, I wouldn’t want pregnant women to be exposed to pesticides, including glyphosate. It’s more from an abundance of caution rather than these two papers. However, I remain unconvinced that glyphosate causes autism spectrum disorder – and I’m very unconvinced that glyphosate in vaccines is actually an issue.

Simple math. Photo by Crissy Jarvis on Unsplash.

Is there glyphosate in vaccines?

Actually, there is glyphosate in vaccines. But let’s get back to real toxicology – what’s the dose, and does it have any biological importance?

The data comes from a “study” that has not been released for anyone to review, let alone being published in a peer-reviewed journal. This is like the garbage that comes from the Italian anti-vaccine group, Corvelva, In this case, a company called Microbe Inotech, which seems to be anti-Monsanto, claims to have the expertise to perform very sophisticated assays for glyphosate.

They claim that they found (again, without any supporting evidence) the following amounts of glyphosate in vaccines:

  • Influenza vaccine, 0.331 parts per billion (ppb)
  • MMR vaccine, 2.671 ppb
  • Pneumococcal vaccine, 0.107 ppb
  • Hepatitis B vaccine, 0.325 ppb
  • T Dap vaccine, 0.123 ppb

This is why we have peer-review. We don’t know what type of testing they did. We don’t know what kind of contamination was found in control samples. We don’t know which vaccines were tested. We don’t know the statistical values. We have nothing.

But there’s more. what do parts per billion mean in real life? Does this meet the standard of “the dose makes the poison”?

Vincent Iannelli, MD, wrote about the importance of these values in his Vaxopedia website:

Or you could think of a ppb as:

  • • one silver dollar in a roll stretching from Detroit to Salt Lake City,
  • • one sheet in a roll of toilet paper stretching from New York to London,
  • • one second in nearly 32 years, or
  • • one pinch of salt in 10 tons of potato chips
  • Michelle McGuire, a professor in the WSU School of Biological Sciences, and who did the studies that didn’t find glyphosate in US breast milk, says that she wouldn’t trust this new report on glyphosate in vaccines. According to Dr. McGuire, “unless the ELISA has been validated and optimized for the matrix of the vaccine, false positives are expected.”

Wait a minute, we can test for glyphosate in breastmilk. And the two studies that claim that glyphosate causes autism couldn’t expend the effort to check that to determine if the herbicide is actually in these women who gave birth to children with ASD?

Nevertheless, these are tiny amounts even if we are to assume that the amounts shown above are accurate. However, we have zero convincing data of what level of glyphosate would increase the risk of autism (if it even does, we need to remember that). 

Let’s say that the level of glyphosate in vaccines is 0.5 ppb, which converts to about 0.0000005 mg of glyphosate in one vaccine dose. So if that is injected in a 10 kg (about 22 pounds in the barbarian scale), it would be 0.00000005 mg/kg. That’s a tiny number. 

The acute oral LD50 for glyphosate in rats is 4320 mg/kg. In other words, using simple maths, the LD50 is about 86.4 billion (yes, billion) times more than in one vaccine. However, glyphosate is cleared quickly, so the tiny vaccine dose basically is gone from the blood within a few minutes. The dose from vaccines, if the “study” is accurate, is so tiny that falls way over to the right on a dose-response curve, at the point where there is no response. 


This is pretty simple:

  1. We have no evidence that vaccines cause autism. And we have no evidence that glyphosate causes autism.
  2. Even if we believe that glyphosate causes autism, we have no dose-response study that shows us at what level it might be linked to autism. That data is critical to determining if there are correlation and causation.
  3. The amount in vaccines, if the data are accurate (which is not supported by any unbiased evidence), is way below any amount that would have a biological effect. 
  4. Finally, we have a tremendous amount of evidence that vaccines are not linked to autism. So even if we had evidence that it did. Even if we had evidence that the amount in vaccines may cause autism. We know that vaccines are not linked to autism, so this is just not important.

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Michael Simpson

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