Does RoundUp cause cancer?

(Quick answer: probably not. See my update at the bottom of this post.)

For many years, environmental activists have been concerned about the herbicide glyphosate, which is the main ingredient in RoundUp®, the world's most widely-used weed killer. Since 1996, global usage of glyphosate has increased 15-fold, in part due to the widespread cultivation of "RoundUp Ready" crops, which are genetically modified to be resistant to RoundUp®. This allows farmers to use the herbicide freely, killing undesirable weeds without harming their crops.

RoundUp®'s manufacturer, Monsanto, has long claimed that glyphosate is safe, and they point to hundreds of studies that support their argument.

Nonetheless, a new study raises the question again.

First let's look briefly at another recent study. A bit more than a year ago, in November 2017, a large study in the Journal of the National Cancer Institute looked at nearly 45,000 glyphosate users (farmers and other agricultural workers who apply glyphosate to crops). These "users" have a much higher exposure to RoundUp® than ordinary people. That study concluded:

"no association was apparent between glyphosate and any solid tumors or lymphoid malignancies overall, including NHL [non-Hodgkin lymphoma]."

They did find, though, that there was a trend–not quite significant–towards an increased risk for one type of leukemia, AML. This trend appeared in users who had the highest exposure to RoundUp®.

In the new study, by a group of scientists from UC Berkeley, Mount Sinai School of Medicine, and the University of Washington, the authors (L. Zhang et al.) decided to focus exclusively on people with the highest exposures to glyphosate. They point out that including people with low exposure, who might have no increased risk of cancer, tends to dilute risk estimates. Statistically speaking, this is undeniably correct, but it also means that their results may only apply to people with high exposures, and not to ordinary consumers.

The punchline from the new study: people with the highest exposure to glyphosate had a 41% higher risk of non-Hodgkin lymphoma.

One caveat to this finding is that it's a meta-analysis, meaning the authors did not collect any new data. Instead, they merged the results from six earlier studies including over 65,000 people, and they focused on those with the highest exposure levels.

Meta-analyses can be prone to cherry-picking; that is, picking the studies that tend to support your hypothesis. However, I couldn't find any sign of that here. The authors include a frank assessment of all the limitations of their study, and they also point out that multiple previous studies had similar findings, although most found smaller increases in relative risk. In the end, they conclude:

"The overall evidence from human, animal, and mechanistic studies presented here supports a compelling link between exposures to GBHs [glyphosate-based herbicides] and increased risk for NHL."

A couple more caveats are important. First, this finding is all about relative risk. Non-Hodgkin lymphoma is one of the most common cancers in the U.S. and Europe, but the lifetime risk for most people, according to the American Cancer Society, is just 1 in 42 (2.4%) for men and 1 in 54 (1.9%) for women. A 41% increase in relative risk increases those numbers to 3.4% (men) and 2.6% (women).

Second, this higher risk only applies to people with very high exposure to glyphosate: primarily people who work in agriculture and apply RoundUp® to crops. Ordinary consumers (including people who eat "Roundup Ready" crops) have a far, far lower exposure, and dozens of studies have failed to show any increased risk of cancer for consumers. For most of us, then, this new study should not cause much concern, but for agricultural workers, it does raise a warning flag.

[Update 18 Feb 7:45pm] After I posted this article, the scientists at the Genetic Literacy Project pointed me to Geoffrey Kabat's piece about the Zhang et al. study. Kabat did a deep dive into the studies that Zhang et al.'s work is based on and uncovered a critical flaw in the study, one that I hadn't found. More than half of the "weight" of the meta-analysis by Zhang, and by far the largest number of cancer cases, come from a single study by Andreotti et al. published in 2018. That study reported risks for 4 different time points: 5, 10, 15, and 20 years. It turns out, as Kabat reports, that only the 20-year period showed any increase in risk of cancer. The relative risks of cancer at 5, 10, and 15 years were actually lower in the group exposed to glyphosate, and yet Zhang et al. didn't mention this fact.

Now, no one thinks that glyphosate lowers the risk of cancer, but Zhang et al. did not report that they had cherry-picked in this way. At a minimum, they should have reported what their findings would be if they used the other time periods. I suspect that they'd have found no increased risk of cancer–but this wouldn't make for such a catchy headline. This omission on their part is a serious flaw, indicating that they (and their results) might have been unscientifically biased.

The bottom line: even in those with very high exposures to glyphosate, the evidence that it causes any type of cancer is very weak. And for ordinary consumers, there's nothing to worry about.

Controversial GMO corn study being retracted over the authors' objections

Retractions are always interesting. When a scientific paper is retracted, it usually means the authors have found a serious error, and that the major conclusions are no longer valid. The error can be unintentional, but in some high-profile cases, the story is far more interesting.

Reading about a retraction is, for a scientist, kind of like reading about a celebrity divorce. You know something went wrong, and it just might be a bit scandalous.

Last year, I wrote a detailed takedown ("Does genetically modified corn cause cancer?") of a very poorly done scientific study by Gilles-Eric Seralini and colleagues, in which they claimed that genetically modified corn, Roundup Ready® corn, caused cancer in rats.  The study had many egregious flaws, and I explained a few of them after reading the paper.  Hundreds of other scientists criticized the study at the time, and six French science academies took the unusual step of issuing a joint statement that rejected the study's conclusions.

Among the many flaws, the study used far too few rats to make statistically valid conclusions, and it contained self-contradictory results, such as data showing that rats fed the highest amount of GMO corn lived longer than rats fed the lowest amounts.  They also used a strain of rats that is highly prone to cancer.  Basically, it was unconvincing junk science.

Last week, Retraction Watch reported that this paper is being retracted. Particularly interesting was the news that the retraction is being made by the editors of the journal, not by Seralini and his co-authors, who are pretty darned upset about it. The journal conducted a lengthy investigation (much too lengthy, I might add - they should have been able to act more quickly) and decided that the many flaws in the paper mean that its major findings are not valid.  It is very unusual for editors to force a retraction like this, especially when fraud is not involved. The journal, Food and Chemical Toxicology, issued a statement that said:

"A more in-depth look at the raw data revealed that no definitive conclusions can be reached with this small sample size regarding the role of either NK603 [RoundupReady corn] or glyphosate [Roundup] in regards to overall mortality or tumor incidence. Given the known high incidence of tumors in the Sprague-Dawley rat, normal variability cannot be excluded as the cause of the higher mortality and incidence observed in the treated groups."

In other words, the editors concluded that Seralini's results were not supported by the data. Together with the rest of their statement, it seems pretty clear the editors are admitting that they screwed up during the peer review process, and they never should have published the article.

Seralini is very unhappy.  So unhappy, in fact, that he's threatening a lawsuit, as Forbes contributor Jon Entine reported.

But is this grounds for retraction? Lots of bad science gets published, often due to sloppy peer review, and most of these papers aren't retracted. In this case, it's pretty clear that the high-profile nature of the paper played a role.  Seralini is part of an anti-GMO organization, CRIIGEN, which has used this paper as justification for an aggressive campaign to ban GMO crops in Europe and elsewhere.

As bad as this study is, and as much as I'd like to see it retracted, I'm not sure that the justification given by the editors of Food and Chemical Toxicology is sufficient for retraction. Maybe it's because their statement is too carefully worded - wimpy, in fact. If they just came out and stated clearly that the study's conclusions are erroneous, then they would have a much better case for forcing the retraction. But they don't quite say that.

Here's what they are trying to say: "we screwed up and did a shoddy job in the peer review process, and now we realize that we never should have published this piece of dreck. Now we want to retract it so that no one will associate our journal with this bad science."

I know some very good scientists who have retracted papers merely because they couldn't replicate the results, and they grew worried that something was wrong. That's how science should work: rather than publish something erroneous, most scientists will admit their errors and retract their findings, or at least issue a correction. Obviously, Seralini has no plans to do this. His intent on publishing this paper was to make a political point, not a scientific one, and he distorted his findings in the paper itself, overstating his results with insufficient statistical evidence, and more so in statements to the press.

Retractions are indeed interesting. I'm still not sure the journal did the right thing to retract this paper, but I know they never should have published it in the first place.

(And for those who don't have time to look at the controversy after the original study: no, genetically modified corn does not cause cancer. Not even a little bit.)

GM corn causes cancer in rats: a study in bad science

Last week a scientific paper appeared that reported that eating genetically modified (GM) corn causes cancer in rats.  Specifically, the scientists fed Roundup Ready® corn, or maize, to rats for two years, and reported that both females and males developed cancer and died at higher rates than controls.  

This is very surprising.  If GM corn causes cancer, why aren't Americans "dropping like flies," as one scientist asked?  We've been eating Monsanto's Roundup Ready® corn for over a decade, even if most of us aren't aware of it.  But our rates of cancer haven't increased more than Europeans, who eat far less GM corn.  Maybe the effect is limited to rats - in which case we should also have seen dramatic increases in cancer in lab rats.  But we haven't seen that either.

So what's wrong?  The best way to find out is to read the paper, which I did.  It turns out to be a very badly designed study, and the report itself omits many crucial details that may (and probably do) completely invalidate the findings.  The scientists leading the study have a strongly biases agenda and a conflict of interest, which they failed to reveal. I'll explain below, but meanwhile this study has already been taken up by politicians as proof (proof!) that GMO crops are harmful.  As Forbes blogger Tim Worstall explained, this paper is more politics than science.

Let's look at the study itself, which was led by Gilles-Eric Seralini (more on him below) and published last week in Food and Chemical Toxicology.  (A copy of the full paper is here.)

The authors studied 200 rats for 2 years, dividing them into 20 group of 10 rats each.  The test rats were fed a variety of diets:

1. Non-GM corn comprising 33% of the diet (this was the control group).
2. Roundup Ready corn comprising 11%, 22%, or 33% of the food.
3. Roundup Ready corn that had been treated with Roundup during cultivation.
4. Non-GM corn but with Roundup itself added to the rats' water.

So what happened?  Well, in some groups, the rats got more cancer than controls.  But not always.  In fact, the authors had to cherry-pick their own data to support their conclusions.

One major problem is that only 10% of the rats were controls - 10 male, 10 female. The study's main claim is that rates of cancer were significantly higher in the rats fed GM corn.  Martina Newell-McGloughlin from UC Davis, in an interview with Discovery News, said 

"The type of statistical analysis they used is really a type of fishing expedition.  One individual referred to it as 'fantasy statistics.' "

Another major problem is that there's no dosage effect.  In other words, if Seralini is right and GM food is bad for you, then more of it should be worse.  But the study's results actually contradict this hypothesis: rats fed the highest levels of GM corn lived longer than rats fed the lowest level.

A third problem, as Discovery News and other sources reported, is that the rats used in this study are a special laboratory strain that is highly prone to cancer.

Perhaps most damning, though, is the fact that rats fed Roundup directly had the longest survival times.  As Seralini's own Figure 1 shows, the longest-living rats in the entire study, out of all the conditions, where those that drank Roundup in their water.  These rats outlived the control rats.

Yum!  Maybe Perrier should start selling Roundup-enhanced spring water?

Seralini and colleagues struggle to explain the internal contradictions in their study.  They write, 

"Interestingly, in the groups of animals fed with the NK603 [Roundup Ready corn] without R[oundup] application, similar effects with respect to enhanced tumor incidence and mortality rates were observed."  

This tortured English is their way of admitting that rats did worse ("similar effects") when fed GM corn that was grown without Roundup.  They don't want to admit that this result contradicts their central hypothesis.

The study was designed to fail: the sample sizes (10 rats in each group) are so small that all the results are likely just due to chance, and none of the differences are meaningful.  It's exceedingly unlikely that the Roundup in the rats' water made them live longer, just as it's unlikely that Roundup Ready corn had any effect on the incidence of cancer.

I know that ad hominem attacks aren't valid, but I can't resist pointing out that Seralini's co-author, Joel de Vendomois, is a homeopath, with a "Homeopathy and Acupuncture Diploma", a double dose of quackery in a single degree.  Seralini has also published a book about the supposed dangers of GMOs, and he and de Vendomois are the lead scientists at CRIIGEN, an organization devoted to lobbying against GMOs. Of course, even if Seralini and de Vendomois are bad scientists, and even if they have a strong bias, their paper isn't necessarily wrong.  It's wrong simply because the science is wrong.

Not surprisingly, an anti-GMO group in California has gleefully embraced the claims of this dreadful paper to argue in favor of Proposition 37, a ballot initiative that will require labelling of genetically modified foods.  And Jose Bove of the European Parliament has used it to claim that all GM crops are harmful to human health.

Let's be clear about the science here.  Genetic modification of foods is a powerful technology that can be incredibly beneficial.  The recent development of salmon that can grow faster is an example: these salmon (developed by a company called AquaBounty) will make fish farming more efficient, and thereby help preserve the perilously endangered wild fish species in our oceans.  On the other hand, GM technology can be used, as Monsanto has done, simply to allow farmers to use more pesticides, which doesn't seem to benefit anyone other than the pesticide producers.  It's unfortunate that Monsanto's behavior has been used as an excuse to give all GMOs a bad name.

Now we have a bad study done by anti-GMO scientists who have allowed their political agenda to trump their scientific judgment.  What a mess.