Dec 03 2013
Elsevier has announced that they are retracting the infamous Seralini study which claimed to show that GMO corn causes cancer in laboratory rats. This is to the anti-GMO world what the retraction of the infamous Wakefield Lancet paper was to the anti-vaccine world. At least this retraction only took one year.
The Seralini paper was published in November 2012 in Food and Chemical Toxicology. It was immediately embraced by anti-GMO activists, and continues to be often cited as evidence that GMO foods are unhealthy. It was also immediately skewered by skeptics and more objective scientists as a fatally flawed study.
The study looked at male and female rats of the Sprague-Dawley strain of rat – a strain with a known high baseline incidence of tumors. These rats were fed regular corn mixed with various percentages of GMO corn: 0 (the control groups), 11, 22, and 33%. Another group was fed GMO corn plus fed roundup in their water, and a third was given just roundup. The authors concluded:
The results of the study presented here clearly demonstrate that lower levels of complete agricultural glyphosate herbicide formulations, at concentrations well below officially set safety limits, induce severe hormone-dependent mammary, hepatic and kidney disturbances. Similarly, disruption of biosynthetic pathways that may result from overexpression of the EPSPS transgene in the GM NK603 maize can give rise to comparable pathologies that may be linked to abnormal or unbalanced phenolic acids metabolites, or related compounds. Other mutagenic and metabolic effects of the edible GMO cannot be excluded.
Sounds pretty scary. Now let’s look at the multiple criticisms:
The biggest criticism of the study is the combination of two features – the small sample size and lack of statistical analysis. The entire study is premised on comparing various dose groups with control groups that were not exposed to GMO or Roundup. And yet, the authors provide no statistical analysis of this comparison. Given the small number of rats in each group, it is likely that this lack of statistical analysis is due to the fact that statistical significance could not be reached.
In other words – the results of the study are uninterpretable. In the retraction statement Elsevier wrote:
Ultimately, the results presented (while not incorrect) are inconclusive, and therefore do not reach the threshold of publication for Food and Chemical Toxicology.
The retraction reads like a long excuse for the editorial failure of the journal, and is disappointing. But at least they ultimately reached the correct conclusion – this paper should never have been published. It slipped through the cracks of peer-review.
If you look at the survival curves for the various groups, I think you will see that the results are all over the place. This is a typical scatter of data with no clear pattern. In the male groups, the GMO and Roundup groups tended to do better, if anything. In the female groups they did worse, but there is no clear dose-response effect evident. Inconclusive is being polite – the data do not show anything, especially absent any statistical analysis.
The study has also been criticized for their choice and treatment of animals. Choosing a strain with a very high background rate of tumor is asking for lots of noise in the data. In fact, a study of the strain found:
The total tumor incidences were 70 to 76.7% and 87 to 95.8% in males and females, respectively.
Further, many scientists charged that the rats were not treated ethically. It is standard practice in such studies to establish an endpoint, such as tumor number and size, at which point the animal with be euthanized. In this study the rats were allow to die of their tumors. The more cynical critics of the study speculate that this was done in order to generate graphic images in order to have the intended effect on public opinion.
The Seralini study suffers from small sample size, lack of statistical analysis, ambiguous results, a questionable selection of rat strain which maximizes noise in the data, and dubious ethical treatment of the animals for possible dramatic effect. At this point anyone referencing this study as support for their position that GMO has health risks sacrifices their credibility.
It helps that the study has now officially been withdrawn, but references to the study in anti-GMO literature are spread across the internet. The damage is done.
The study is similar in quality to the Carman pig stomach study – which was also worthless but presented as evidence that GMO is bad. This study also took a random scatter of data and then hunted for any possible illusion of a signal in the noise.
Meanwhile, systematic reviews of the research show no evidence for any health risk from GMO foods.
The bigger issue with the Seralini study, however, is peer-review itself. I do not expect any system to be perfect, and it is reasonable for journals to publish articles that are in the gray zone so that the community can do post-publication peer-review. I do not, however, think the Seralini study was in the grayzone, as the retraction acknowledges.
Rather than apologizing for the process, as the Elsevier retraction statement does, I would prefer this be used an an opportunity to tighten the peer review process. Given the proliferation of journals and competition for the public’s attention, we need a movement to increase quality control in science publication.
This should be especially true in a controversial area where a study is likely to have political ramifications. This study should have been given closer scrutiny prior to acceptance. For example, the raw data could have been requested for review prior to publication. A cynical critic might suspect that the journal was more concerned with headlines and its impact factor than with strict quality control.
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