Before speculating about the reason for the “explosive” increase in autism, one has to make sure the explosion is real. 

In 1943, a famous paper was published in which Leo Kanner, a child psychiatrist at Johns Hopkins, described a series of children with “fascinating peculiarities.” He thought that these characteristics form a unique syndrome,’ not heretofore reported, which seems to be rare enough, yet is probably more frequent than is indicated by the paucity of observed cases.” He called the syndrome autism. 

What causes autism? It is now broadly considered to be a multi-factorial disorder resulting from genetic and non-genetic risk factors and their interaction.” Autism spectrum disorder (ASD) can run in families, but genetic factors may account for only 10 to 20 percent of cases. This is based partly on the fact that you can have identical twins with identical DNA—the exact same genesand one twin may have autism, but not the other. “While genetic susceptibility may be a key contributor to ASDs, it may conceptually just load the gun so to speak, with prenatal, perinatal, and/or postnatal environmental exposures”—that isenvironmental exposures during, around, or after pregnancy—“being the events that pull the trigger and may give rise to the disease.  

This is good news for those that want to reduce the number of cases. The larger the role these non-genetic factors play in causing autism, the more modifiable the risk factors may be, potentially open[ing] up avenues for the primary prevention ofautism in the first place.  

Since autism was first described as a medical condition in 1943its prevalence has exploded from 1 in 5000 individuals to 1 in 68.2”—now more than 1 percent of the population, about a 7,000 percent increase. As you can see at 1:48 in my video Is Autism Really on the Rise?data do indeed show an exponential increase from virtually no diagnosed cases in the early 1900s to the prevalence of autism shooting through the roof in the 1980s and 1990s. What happened around that time that could account for the explosion? Hold on. It makes sense that there weren’t any diagnosed cases in the early 1900s; it didn’t even have a name until 1943. But, aKanner said in the original paper, there probably were more cases out there, but they just hadn’t been looking. So, the early data we have do not show the prevalence of autism; they show the prevalence of autism diagnoseswhich are dependent on the diagnostic criteria you are using and whether you’re even looking for ASD or not. 

Put another way, historical prevalence estimates for autism and the broader autism spectrum might well have been underestimates of the true prevalence.” Perhaps a lot of cases were missed“Increased recognition [among doctors and society at large], the broadening of the diagnostic concept over time and methodological differences across studies may account for most or all of the apparent increase in prevalence, although this cannot be quantified. So, before we start speculating about the reason for the explosive increase, maybe we should first make sure the explosion is real. The bottom line? While we may never really know what the prevalence of autism was a half century ago, we do have decent data over the last few decades that do point to a considerable increase in the true prevalence.  

Maybe there wasn’t actually a 22-fold increase in autism in the 1980s and 1990s. Maybe there was actually only an eightfold increase. We may quibble over whether the increase was 800 percent or closer to 2000 percent, but it seems that autism rates truly are increasingso the question legitimately turns to why? 

This is an important concept. When we talk about the prevalence or incidence of disease, we are talking about the prevalence or incidence of diagnosis. So, if criteria change or if we just look harder, artefactual changes can be created in disease rates. 


Autism was first described in a paper published in 1943 by Leo Kanner, a child psychologist at Johns Hopkins, who identified “fascinating peculiarities” in a series of children that he thought formed a unique “syndrome.”
Today, autism spectrum disorder (ASD) is considered to be a multi-factorial disorder with genetic and non-genetic risk factors. 

The more significant the role non-genetic factors may play in causing ASD, the more “modifiable” the risk factors may be, which could potentially allow for prevention of the disorder in the first place.  
It appears that the prevalence of autism has “exploded” since it was first described in 1943 with about a 7,000 percent increase, but early data do not show the prevalence of autism—only the prevalence of autism diagnoses, which are dependent on the diagnostic criteria being used, as well as whether or not ASD is even being investigated. 
We may never know what the prevalence of autism was a half century ago, but data from the last few decades point to a considerable increase in the true prevalence.  
It’s important to differentiate between the prevalence or incidence of disease and the prevalence or incidence of diagnosis.

Look for my video The Role of Pesticides and Pollution in Autism. And, if you missed any of my other videos on preventing and treating ASD with diet—and are interested in preventing and treating autism, that is, and I am well aware that not everyone is!see: 

Fever Benefits for Autism in a Food

Fighting Autism Brain Inflammation with Food 

Best Foods for Autism 

Autism and Casein from Cow’s Milk 

Does A2 Milk Carry Less Autism Risk? 

Gluten-Free, Casein-Free Diets for Autism Put to the Test 

Are Autism Diet Benefits Just a Placebo Effect? 

DoubleBlind Clinical Trial of Diet for Autism 

Pros and Cons of Gluten-Free, Casein-Free Diets for Autism 

The Role of the Gut Microbiome in Autism
Flashback Friday: The Best Foods for Fighting Autism and Brain Inflammation 

In health, 

Michael Greger, M.D. 

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: 

2019: Evidence-Based Weight Loss 

2016: How Not To Die: The Role of Diet in Preventing, Arresting, and Reversing Our Top 15 Killers 

2015: Food as Medicine: Preventing and Treating the Most Dreaded Diseases with Diet 

2014: From Table to Able: Combating Disabling Diseases with Food 

2013: More Than an Apple a Day 

2012: Uprooting the Leading Causes of Death