Is High Fructose Corn Syrup Responsible For A Dramatic Spike In Autism Rates?

A review of existing research published in Clinical Epigenetics last month has generated quite a stir of dramatic headlines like “New Study Links Autism To High-Fructose Corn Syrup” and “High Fructose Corn Syrup And Maternal Obesity: Autism Causes?”  Having a son in the autism spectrum disorder and working for the Corn Refiners Association made the news a real attention grabber for me and I’m sure for anyone else who is personally connected to autism.  It’s very important that we try to understand the variables that we can modify in our lives and environment to reduce risks of autism and other disorders and diseases.  But what happens when people think there’s a silver bullet and modify their lifestyles only to learn that the bullet was the wrong one?  That’s why integrity in science and the media is important, but we have some work to do there.

HFCS & Autism Research: Conclusions & Issues

Let’s first take a look at the research that drove the headlines.  Lead author Rene Dufault and colleagues looked at rising rates of special education services under the autism disability category, geographic gene expression patterns and geographic differences in diet and toxic substance exposure. They concluded:

“A comparison of autism prevalence between the U.S. and Italy using the Mercury Toxicity Model suggests the increase in autism in the U.S. is not related to mercury exposure from fish, coal-fired power plants, thimerosal, or dental amalgam but instead to the consumption of HFCS.”

Issue 1: Mercury

So they are concerned with mercury in HFCS. In this review, Dufault et al., make their mercury claims based on a paper they wrote that was never confirmed. That’s one of the problems.

Emily Willingham, Ph.D., science editor at The Thinking Person’s Guide to Autism, and editor at Double X Science described several concerns she has with the Dufault review in a post for Grist, “Why That Corn-Syrup-And-Autism Study Leaves Such A Sour Taste.” Here’s what she has to say about the mercury link:

“Unfortunately, their assertions of mercury intake via HFCS are also based on their own previous work testing for mercury in HFCS-containing foods, an extremely poorly executed study with gaps so large that even my nonmajors science classes easily identified them. Indeed, an independent assessment from a Duke toxicologist of actual samples of HFCS for mercury, done in response to that study, found ‘no quantifiable mercury in any of the samples tested’ [doc]. In other words, one of the cornerstones of the authors’ argument — mercury in HFCS — is arguably nonexistent.”

Issue 2: HFCS Consumption & Autism Rates

Here’s another problem. Dufault et al. suggest a correlation between rising HFCS consumption and rising rates of autism, but on closer look the data doesn’t really support the argument.  Again, Emily Willingham makes this critique come to life. She created a graph using HFCS consumption trends plotted with trends in autism rates.

From “Why that corn-syrup-and-autism study leaves such a sour taste” on Grist.org

So if the data supported the theory that rising HFCS consumption is directly linked to autism, it would seem that the two trends would increase together.  The chart above shows HFCS consumption peaking and then decreasing while autism rates continue to climb.  We know that correlation does not equal causation, but as Willingham points out:

"The authors don’t even have a fundamental mutual trend between autism and HFCS consumption rates on which to base the rest of their generally unsupported assertions. The house of cards on which the authors’ “model” relies lacks a foundation."

Issue 3: One Geographic Comparison is Not Representative of All

Another major hole in the argument made by Dufault et al. is the attempt to compare dietary habits and rates of autism in the U.S. and Italy to justify the theory that HFCS in the U.S. diet is contributing to rising rates of autism. Again, Willingham helps readers recognize that Italy is a poor example to use because the rates of autism in Italy are not understood very well:

“They take Italy as an example, claiming that Italians consume very little HFCS and, as a result, have low autism rates. What they don’t mention is that Italy has lacked a specific code for autism [PDF – see page 12] and any agreement on classification and diagnostic tools, which makes teasing out actual prevalence a little difficult

Pulitzer-prize winning science journalist, Deborah Blum, questioned the authors’ focus on HFCS as the distinguishing dietary component between the two countries:

“The study compares populations in the US and Italy, where far less corn sweetener is used, but it’s fair to wonder about other dietary differences between these two cultures.”

Do other countries where rates of autism are well documented support the Dufault et al. conclusions? Willingham provided several examples, but one is sufficient to make the point. Here’s what she shared about South Korea:

“A thorough South Korean study identified autism prevalences more than twice than in the latest U.S. data. Yet, 2005 data suggest that South Korean HFCS consumption is considerably less than that in the U.S.”

Responsible Science Reporting: Where’s the Perspective?

I am not a scientist or an academic researcher, but I do feel that it is fair of me to ask: Is it responsible to suggest that mercury in HFCS is a reason for rising rates of autism based on questionable mercury data and a single-country comparison? And then is it fair to present the conclusions of this study as definitive?

Fortunately there are science writers like Emily Willingham, Deborah Blum, and John Timmer, who are willing to take a closer look at the research and the reporting about the research to help put it into perspective.

To be fair, Willingham’s critique of the study was at the request of Grist editor Scott Rosenberg who took action in response to feedback received on the original write up of the Dufault paper by Tom Laskaway titled “New Study Links Autism To High-Fructose Corn Syrup,” in which he states:

“The blaring headline version of the new study’s conclusion would read: ‘High-Fructose Corn Syrup Causes Autism.’ And while that may be a bit of an overstatement, it’s not off by much.”

And there we have the makings of a silver bullet based on flawed research and sensational reporting.

No one can discount the impact of autism on our society or on those it touches. We do need to research and understand how variables in our environment and diets may affect people, especially those who may be more susceptible. I think it’s fitting to end on this quote from Blum from her post “On the corn syrup theory of autism:”

“But if we jump on the bandwagon of every one of these alternative theories and ideas, we do neither our readers or the science itself much service.  Instead, we may only add to misinformation.”