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Monsanto glyphosate (Roundup) is a broad-spectrum systemic herbicide used to kill weeds, especially annual broadleaf weeds and grasses that are known to compete with commercial crops grown around the world. It has several advantages over many herbicides in that it breaks down in the soil into non-toxic organic molecules, reducing or eliminating contamination of groundwater and lower soils.

Monsanto has developed genetically modified (GMO) grains that are resistant to glyphosate, so that agriculture can apply the herbicide to kill the competitive weeds while not harming the crop. This allows farmers to suppress the weeds while allowing better production out of the grain crop.

Whatever the benefits of Monsanto glyphosate, GMOs and the herbicide are tied together in many minds. And there has been an ongoing effort by many people to claim that glyphosate causes cancer. But let’s look at the science, because maybe we’ll get some information.

What’s this about cancer and Monsanto glyphosate?

The famous (or is that infamous?) study from Séralini, which claimed that glyphosate and GMO corn caused cancer in rats, is quite popular with the anti-GMO forces. For many reasons, including bad statistics, improper experimental design, and bad conclusions, the article was retracted by the journal.

Because that article was retracted, it doesn’t actually count because it really doesn’t exist (but to be fair, it was eventually, re-published in a very low ranked journal).. This story is frighteningly similar to the story of that cunning fraud, Mr. Andy Wakefield, who wrote a fraudulent, and ultimately retracted, article about vaccines and autism. I guess Séralini is the Wakefield of the GMO world.

There are better studies out there–maybe. The most recent one is a review from the International Agency for Research on Cancer (IARC), recently published in Lancet Oncology, an extremely high impact factor journal, probably one of the most respected journals in cancer research.

And the IARC, one of the intergovernmental agencies within the World Health Organization, is widely respected for their research into the causes of cancer. According to the IARC,

There was limited evidence in humans for the carcinogenicity of glyphosate. Case-control studies of occupational exposure in the USA, Canada, and Sweden reported increased risks for non-Hodgkin lymphoma that persisted after adjustment for other pesticides. The AHS cohort did not show a signifi cantly increased risk of non-Hodgkin lymphoma. In male CD-1 mice, glyphosate induced a positive trend in the incidence of a rare tumour, renal tubule carcinoma. A second study reported a positive trend for haemangiosarcoma in male mice. Glyphosate increased pancreatic islet-cell adenoma in male rats in two studies. A glyphosate formulation promoted skin tumours in an initiation-promotion study in mice. Glyphosate has been detected in the blood and urine of agricultural workers, indicating absorption. Glyphosate and glyphosate formulations induced DNA and chromosomal damage in mammals, and in human and animal cells in vitro. One study reported increases in blood markers of chromosomal damage (micronuclei) in residents of several communities after spraying of glyphosate formulations. The Working Group classified glyphosate as “probably carcinogenic to humans” (Group 2A).

First, the IARC is very conservative in its writing and conclusions. So it may be that they are much more willing to rate a compound as carcinogenic than not, possibly as an offshoot of the precautionary principle.

Second, the IARC did this “review” over what appears to be a short period of time. The pro-GMO blogosphere, who seem to be falling over themselves to actually appear like Monsanto shills (and very embarrassing to me), cherry pick some of the most ludicrous “attacks” on the IARC review, including this one: ”

On the other hand, reviews of glyphosate by regulating bodies in the United States, Canada, Germany, and other parts of the world take up to 5 years.

That has nothing to do with the quality of the review, just that the EPA and FDA are ponderously slow and deliberative bureaucracies that inhibit free-flow of information. And to assume that those regulatory bodies are reviewing Monsanto’s glyphosate 24/7 is just beyond my ability to shake my head enough.

Third, the IARC does not do original research, again pointed out by the pro-GMO blogging world, which is completely irrelevant.

IARC does not conduct any original research; it only reviews studies and research already published to determine carcinogen status.

The Cochrane Collaboration, probably the platinum standard for publishing systematic reviews, does not do any original or primary research. They do reviews, rolling up the data from multiple studies. In real science, reviews are the pinnacle of science, and represent the best knowledge out there. So this is some sort of strawman argument–because IARC doesn’t do primary research, which real scientists dismiss anyways, they don’t do anything useful.

No.

But the IARC said that Round Up causes cancer!

OK, the IARC has a five step classification of potentially carcinogenic compounds:

Group 1: Carcinogenic to humans

Group 2A: Probably carcinogenic to humans

Group 2B: Possibly carcinogenic to humans

Group 3: Unclassifiable as to carcinogenicity in humans

Group 4: Probably not carcinogenic to humans

Group 2A, in which glyphosate was place, does sound serious. But a common chemical produced by fruits and your own body causes cancer. Formaldehyde, the boogeyman of every antivaccine nut out there. According to the IARC, it’s a Group 1 carcinogen, meaning it’ll definitely cause a cancer. In other words, much more dangerous than glyphosate.

And formaldehyde occurs naturally everywhere. It’s in apples, up to 22 ppm (parts per million). Maybe that old saying about an apple a day should be ended?

No, that would be going too far. Because there is an occurrence of a chemical doesn’t mean it causes cancer. It means it could (or can, in the case of formaldehyde) if the dose is sufficient. There’s a thing called dose response toxicity, which means at what dose is there a response (like cancer). For formaldehyde, the dose that causes cancer is not perfectly known, but it’s generally around 1ppm every second of every hour of every day. You’d have to eat a boatload of apples to do that. Every day.

So don’t drink formaldehyde by the liter, and it’s pretty easy to be way below the dose that increases your risk of cancer.

For glyphosate, there’s a major problem. The link between cancer (of any type) and glyphosate seems to be nonexistent. This is troublesome after reading the IARC report. Much of their research seems to be from:

Results that show glyphosate is in the blood and urine of farmworkers. This doesn’t show any causal link to anything, unless it’s a massive epidemiological study. Some animal studies. And I loathe animal studies to show anything except some mice and rats get force fed glyphosate.

A recent meta-review, published in a real journal, came to a wholly separate conclusion (and remember, I consider meta-reviews to be the pinnacle of real science):

Our review found no consistent pattern of positive associations indicating a causal relationship between total cancer (in adults or children) or any site-specific cancer and exposure to glyphosate.

These researchers based their review on 21 cohort and case-controlled studies. This is extremely powerful evidence that glyphosate doesn’t cause cancer and is unrelated to cancer.

Once again, I’m not drinking a liter of glyphosate with my GMO breakfast cereal. More seriously, I would advocate for lower use of it through glyphosate resistant crops (which allows glyphosate to be used in lower and better controlled amounts).

Sometimes I tire of these XYZ causes cancer fears that sweep through the internet. The fact is, as best as we can tell, there’s 12 steps that one can do to reduce the risk of cancer. Quit smoking. Stay out of the sun. Stay fit. Don’t drink too much. None of it says for you to quit eating apples or avoiding glyphosate.

But there are over 200 cancers, probably close to 250. Each one has a separate cause and pathophysiology. Mostly, the body removes cancers, unless there are a series of 5-10 mutations in a cell, and do you know how rare that is, even if the body has 20-50 trillion cells? If glyphosate caused one mutation, that’s still less than what is caused by the sun.

Exposure to glyphosate probably will not cause cancer. Maybe it increases the risk by 1:10,000,000, but that’s over a lifetime. Smoking is much much much worse. Second hand smoke is almost as bad.

Monsanto glyphosate and cancer – summary

The World Health Organization says that Monsanto glyphosate is a carcinogen.

Maybe. But at what dose? Unknown.

Better epidemiological evidence, apparently ignored by WHO, says that glyphosate is not correlated or causal to any cancers.

Pro-GMO people. Attack the science not the people. WHO and IARC make mistakes every once in a while. But they do good work, like the CDC and FDA. In this case, their science seems to be really bad, by ignoring other science. Remember, WHO has said GMO products are probably safe.

I’m going to keep eating my apples. I love apples.

Don’t smoke.

Editor’s Note – This article was first published in March 2015. It’s been revised and reformatted for accuracy, style, and clarity.

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The Original Skeptical Raptor Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!

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