Is Autism Really on the Rise?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

In 1943, a famous paper was published in which a child psychiatrist at Hopkins described a series of children with so-called “fascinating peculiarities.” He thought these characteristics formed “a unique ‘syndrome’” he called autism, which seemed rare at the time. But, who knew how many were out there undiagnosed?

What causes it? Autism is currently “considered…a multi-factorial disorder resulting from [both] genetic and non-genetic risk factors…” Yes, it can run in families, but “genetic factors [may] account for only 10 to 20% of…[autism] cases.” This is based in part on the fact that you can have identical twins, with identical DNA—the same genes, and one identical twin may have autism, and the other not. So: “While genetic susceptibility may be a key contributor to [these autism spectrum disorders], it may…just ‘load the gun’ so to speak, with prenatal, perinatal, and…postnatal environmental exposures [some kinds of exposures during, around, or after pregnancy] being the events that ‘pull the trigger’ and may [actually] give rise to [the disease].”

This is good news. I mean, 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 as a medical condition was first described, the prevalence of autism has apparently exploded from like “1 in 5000 individuals to 1 in 68…” now—more than 1% of the population. That would be like a 7,000% increase. And, indeed, you’ll see graphs like this: showing an exponential increase in the prevalence of autism, from like no diagnosed cases in the early 1900s, to the prevalence shooting through the roof in the 80s and 90s.

And so, that immediately gets you thinking: what happened around that time that could account for the explosion? But, wait a second. Of course, there were no diagnosed cases in the early 1900s; it didn’t even have a name until 1943. As Kanner said in the original paper, there’s probably more cases out there, but they just hadn’t been looking. So, this isn’t a graph of the prevalence of autism; it’s a graph of the prevalence of autism diagnoses, and that depends on what diagnostic criteria you’re using, and whether you’re out there looking for it or not.

“Put another way, historical prevalence estimates for autism…[and its rarity] might well have been underestimates of the true prevalence” back then; may have just been missing lots of cases. The “[i]ncreased recognition among doctors” and society at large, the “broadening of the diagnostic concept over time” and different studies using different criteria may account for [much] of the apparent increase in prevalence, although this [can’t] 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 is that, while we may never really know what the prevalence was a half century ago, we do have decent data over the last few decades that really does point to a considerable increase in the true prevalence.

So yeah, maybe there wasn’t actually a “22…-fold increase” in autism in the 80s and 90s; maybe there was actually only an “8…-fold increase.” So yeah, we may quibble whether the increase was 800%, or closer to 2,000%, but the bottom line seems to be autism rates are really increasing. And so, the question legitimately then turns to why—which we’ll explore, next.

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Image credit: Michał Parzuchowski via Unsplash. Image has been modified.

Motion graphics by Avocado Video

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