How Real Is the Rise in Autism Rates?

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Before debating the possible reasons for the “explosive” increase in autism, we need to know if the explosion is real.

In a famous paper published in 1943, Leo Kanner described a series of children with “fascinating peculiarities.” The child psychiatrist at Johns Hopkins University wrote 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 multifactorial disorder resulting from genetic and non-genetic risk factors and their interaction. Although autism spectrum disorder (ASD) can run in families, genetic factors may account for only 10 percent to 20 percent of all cases. Indeed, despite identical twins having identical DNA — the exact same genes — 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 is, environmental exposures during, around, or after pregnancy may be “the events that ‘pull the trigger’ and may give rise” to the disease.

For those who want to reduce the number of cases of ASD, this is good news. 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 of…autism” in the first place. 

Since autism was first described as a medical condition in 1943, its prevalence “has exploded from 1 in 5,000 individuals to 1 in 68.2” — now more than 1 percent of the population, which is an increase of about 7,000 percent. As you can see at 1:48 in my video Is Autism Really on the Rise?, data show an exponential increase from virtually no diagnosed cases in the early 1900s to the prevalence of autism skyrocketing in the 1980s and 1990s. What could account for the explosion? Certainly, it makes sense there weren’t any diagnosed cases in the early 1900s since it wasn’t even named until 1943. But, as Kanner said in the original paper, there probably were more cases out there. They just hadn’t been looking for them. So, that early data do not show the prevalence of autism. Instead, they show the prevalence of autism diagnoses, which are dependent not only on the diagnostic criteria being used, but on whether or not you’re even looking for ASD.

“Put another way, historical prevalence estimates for autism and the broader autism spectrum might well have been underestimates of the true prevalence.” A lot of cases may have been 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 begin speculating about the reasons for the explosive increase in ASD cases, perhaps we should 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 pointing 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 only an eightfold increase. Even if we quibble over whether the increase was 800 percent or closer to 2,000 percent, it appears that autism rates truly are increasing. So, 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. If criteria change or if we simply look harder, artifactual changes can be created in disease rates.

This content was first published on NutritionFacts.org.

Tags: parenting, wellness, autism

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Written By

Dr. Michael Greger

A founding member and Fellow of the American College of Lifestyle Medicine, Michael Greger, MD, is a physician, New York T... See Full Bio

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