I keep reading the claim that somehow glyphosate, also known as Roundup, is linked to cancer, despite numerous large epidemiological studies that have yet to provide evidence of a link that would convince us that the herbicide has any link to any cancer.
One of the major issues with the tropes and myths about glyphosate is that many people tend to conflate glyphosate with genetically modified crops (GMOs). This leads to a lot of unsupported hatred of GMO plants, despite the overwhelming scientific consensus that says that GMO agriculture is safe for humans, animals, and the environment – a consensus as broad and powerful as the one that states that climate change is caused by humans.
Glyphosate is so hated, I don’t know how many times I write that GMOs are safe, and they are safe — then someone will write back, “yeah but Monsanto is killing us with their cancer-causing glyphosate.” It’s frustrating, but that’s the usual state of my mind when dealing with pseudoscience-pushing people.
However, I have actual scientific evidence that supports the claim that there is no link between glyphosate and any of the 200 or more types of cancer. I know some people, especially greedy attorneys, will cherry-pick poorly designed primary studies and ignore the larger systematic reviews and meta-analyses that show no link.
I’m going to give you a brief review of some of the most powerful studies, which are at the top of the hierarchy of biomedical research, that reject any claims that glyphosate causes cancer.
What is glyphosate?
Glyphosate (Monsanto’s 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 within a few days to weeks, reducing or eliminating contamination of groundwater and lower soils. This is a large improvement over other types of herbicides.
Roundup, which was produced by Monsanto and is usually blamed for everything bad, is now off-patent and manufactured by a lot of different companies under different brand names. Glyphosate is one of the most popular weed killers in the world.
Glyphosate’s mechanism of action is to attach itself to the enzyme EPSP synthase. When glyphosate binds to this enzyme, it becomes non-functional, and the plant is unable to make the crucial amino acids phenylalanine, tyrosine, and tryptophan. The plant slowly dies without these amino acids.
In case you’re wondering, EPSP synthase is not found in animals, so when humans or pets are exposed to glyphosate, it has nothing to bind to and is excreted almost intact with virtually no effect. I cannot emphasize this enough — glyphosate has no known mechanism of action in humans, livestock, or any other animal because we animals don’t have EPSP synthase. For animals, humans included, glyphosate is innocuous and is just excreted like many other compounds that are inert in humans.
Monsanto developed genetically modified (GMO) grains that are resistant to glyphosate so that farms 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 of the grain crop. There is robust evidence that glyphosate has no effect on crop yield while reducing pests at a lower cost than other modalities.
Whatever the benefits of Monsanto glyphosate, GMOs and glyphosate are tied together in many minds. And there is a “chemophobia” amongst many people that all chemicals are bad. But as I discussed before, the dose makes the poison – that is, in the real study of toxicology, there are doses of any “chemical” that are safe or unsafe. Water, for example, can be toxic if consumed at certain doses – sure, the dose is high for water toxicity, but it exists. Our culture’s chemophobia makes no sense to people, like me, who understand chemicals – every single thing we consume is made of evil chemicals, some with complex and indecipherable names.
Of course, as a result of this chemophobia, and misinterpreted scientific research, there has been an ongoing effort by many people to claim that glyphosate causes cancer. This, of course, has led to a Monsanto bashing across the internet along with several lawsuits. My article is agnostic about Monsanto – I just don’t care about the company one way or another. All I care about is the quality of evidence that either supports or refutes the hypothesis that glyphosate is linked to cancer.
We’ll look at the new study that has been released examining that hypothesis. I guess if you hate Monsanto and RoundUp, you’ll be disappointed with the evidence from real science. But you know what they say – everyone loves science unless it contradicts their beliefs.
No link between glyphosate and cancer
Let’s take a look at the highest quality research, that is, systematic reviews and meta-analyses that examined links between glyphosate and cancer:
- The research, published in the Journal of the National Cancer Institute (JNCI) and written by Gabriella Andreotti et al., represented a large, long-term study on the use of glyphosate by agricultural workers who handle the chemical. The published study included nearly 45,000 workers in Iowa and North Carolina who had licenses to handle glyphosate. The researchers found no statistically significant link between exposure to the herbicide and cancer. The study found no association between glyphosate “and any solid tumors or lymphoid malignancies overall, including non-Hodgkin Lymphoma . . . and its subtypes.”
- A systematic review of 21 case-control and cohort studies, published in Regulatory Toxicology and Pharmacology, came to this conclusion:
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.
- A meta-analysis, published on 24 February 2020 in La Medicina del Lavoro concluded that their analysis “…provided no overall evidence of an increased risk for both NHL (non-Hodgkins lymphoma) and MM (multiple myeloma) in subjects occupationally exposed to glyphosate.”
- A systematic review, published in September 2016 in Critical Reviews of Toxicology concluded that “…our review did not find support in the epidemiologic literature for a causal association between glyphosate and NHL or MM.”
- A systematic review and meta-analyses, published on 25 March 2016 in the Journal of Environmental Science and Health B, concluded that “…a causal relationship has not been established between glyphosate exposure and risk of any type of LHC (lymphohematopoietic cancer).”
- Just so you know I am not cherry-picking, a meta-analysis published on 22 December 2021 in the Environmental Toxicology and Pharmacology, concluded that “prenatal pesticide exposure is associated with an increased risk of neuroblastoma.” However, this study combined results from six different pesticides, and the authors did not establish the risks of the individual products. The study isn’t really powered to tell us if one pesticide is more or less dangerous than the others.
Why do people believe glyphosate causes cancer?
Many individuals refer to the International Agency for Research on Cancer (IARC), an intergovernmental agency within the World Health Organization and one of the widely respected research groups for cancer causes, statements on glyphosate and cancer:
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 significantly 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).
I did an extensive critique of the conclusions of the IARC where I examined several points about their review:
- A lot of their research is based on evidence that shows glyphosate is in the blood and urine of farmworkers. These results do not show any causal link to anything, especially cancer. It has been established that farmworkers who use a lot of glyphosates may show higher blood levels of the chemical. But that’s a long way to demonstrating that glyphosate causes cancer.
- In addition, some of their research is based on animal studies. I am certainly not a fan of animal studies to show anything except some mice and rats might get cancer after consuming rather large quantities of glyphosate. Less than 10% of animal studies ever lead to clinical significance, so making a broad proclamation based on animal studies is not useful.
- They seemed to ignore the high-quality systematic reviews (again, at the top of the heap of biomedical research) that clearly refute the hypothesis that glyphosate causes cancer.
- Finally, 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 a result of the precautionary principle.
Reviewing the most powerful research presented about any association between glyphosate and cancer seems to lead me to the conclusion that glyphosate is “innocent.”
One item that’s necessary to establish causation between glyphosate and cancer is biological plausibility — by what mechanism does glyphosate interact with the DNA to cause damage that would lead to cancer? No one has provided that. It appears that we’re getting nothing more than “it’s a chemical so it must cause cancer.” As I wrote above, glyphosate targets one enzyme in plants that do not exist in animals.
I know, people are going to get mad at this review just because they don’t like the results. They want to believe Monsanto is evil (maybe they are, but not because of glyphosate). They want to believe that glyphosate causes cancer because all chemicals are bad. They want to believe that GMOs are bad because of glyphosate.
- Andreotti G, Koutros S, Hofman JN, Sandler DP, Lubin JH, Lynch CF, Lerro CC, De Roos AJ, Parks CG, Alavanja MC, Silverman DT, Beane Freeman LE. Glyphosate Use and Cancer Incidence in the Agricultural Health Study. JNCI: Journal of the National Cancer Institute; djx233. doi: 10.1093/jnci/djx233.
- Acquavella J, Garabrant D, Marsh G, Sorahan T, Weed DL. Glyphosate epidemiology expert panel review: a weight of evidence systematic review of the relationship between glyphosate exposure and non-Hodgkin’s lymphoma or multiple myeloma. Crit Rev Toxicol. 2016 Sep;46(sup1):28-43. doi: 10.1080/10408444.2016.1214681. Erratum in: Crit Rev Toxicol. 2018 Sep 26;:1. PMID: 27677668.
- Chang ET, Delzell E. Systematic review and meta-analysis of glyphosate exposure and risk of lymphohematopoietic cancers. J Environ Sci Health B. 2016;51(6):402-34. doi: 10.1080/03601234.2016.1142748. Epub 2016 Mar 25. PMID: 27015139; PMCID: PMC4866614.
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