Does Glyphosate in Roundup Cause Cancer?

By - November 12, 2018
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How does Roundup and its active ingredient glyphosate cause cancer, including non-Hodgkin lymphoma? This question has been at issue for some time, most recently in a lawsuit in California where a groundskeeper was awarded $289 million by a San Francisco jury because it found Monsanto, the maker of Roundup, had contributed to the man’s health condition.

Also, glyphosate was to be listed in the state of California as a substance known to cause cancer in 2017, although that decision was struck down in federal court.

Much of the litigation and proof that Roundup causes cancer is based upon a 2015 ruling by the International Agency for Research on Cancer, which is part of the World Health Organization, that active ingredient glyphosate is most likely a human carcinogen. While this report has come under some criticism, it is still some evidence that the substance can cause cancer.

What Is the Evidence?

The classification by the IARC relies in part on experiments with mice. But is that enough to definitely prove that the weed killer can cause cancer in humans? That is a debatable point. Many experts believe that if it was so simple to determine what causes cancer in human beings, scientists would just do the proper experiment and the answer would be obvious. But it is not always that simple.

Proving Causation Is Basis of Product Liability Lawsuits

Epidemiology is a science that offers evidence that is needed to prove cause and effect in public health and medicine. It is one of the key tools to determine if exposure to a certain substance boosts the risk of disease. The problem is that it is easy to do epidemiology poorly. A bad study with bad data is worse than not having a study at all.

On that note, after a hearing that examined the science on both sides of the glyphosate debate, US District Judge Vince Chhabria said that epidemiology can be rather ‘loosey goosey,’ and is a ‘very subjective field.’ But he did say that both sides of the debate are reasonable on scientific grounds and should have their day in court with a verdict being decided by a jury.

Comparison to Smoking and Lung Cancer

When one considers proving whether exposure to Roundup causes cancer, it is helpful to think about the issue of smoking and lung cancer. Many epidemiological studies in the last 80 years have demonstrated a strong association between lung cancer and smoking. But there has never been a human randomizing trial on this matter. It also is known that when rats smoke, they do not get lung cancer, according to the study ‘Tobacco Smoke-Induced Lung Cancer in Animals–A Challenge to Toxicology’ published in the International Journal of Toxicology.

For many years, major tobacco companies dismissed countless observational studies in humans by saying that ‘association is not causation.’ They avoided regulation based upon this philosophy. The scientific community was intimidated by this sort of strategy for years. Eventually, clinical studies accumulated to the point that the association was quite overwhelming. At that point, the cause and effect was undeniable.

Two Types of Epidemiological Studies

These are cohort and case-control. In a cohort clinical study, a large group if people, some who are smokers and some who are not, are followed for years to see who becomes ill with cancer. In a case control study, a collection of lung cancer patients are asked about what their smoking history is, along with an equal number of people who do not have lung cancer.

In every cohort study, smokers become more sick with major health problems, including heart disease, lung cancer and other serious health problems over the years. In most of the studies, scientists tried to take into account for many differences between nonsmokers and smokers, so the effects of smoking was isolated. Also, in many case-control studies, patients who had lung cancer were more likely to have smoked than people in the overall population.

How to Define Proof

When scientists are asked to define what ‘proof’ means, most of them mention criteria including reproducibility and statistical significance, as well as plausibility. But who should decide when each criterion has been met? Usually, it is a panel of experts. Many scientists may find it unsettling that proof can only be determined by a panel of experts. But this is really the case in most scientific pursuits. What was proven might be unproven with a new slate of experts or new evidence.

Experts are often chosen via such bodies as the National Academies of Sciences, or advisory boards of various professional societies such as the American College of Cardiology. The makeup of such panels might be challenged, and people might choose to ignore exports and think what they wish.

Is Circumstantial Evidence Enough?

Circumstantial evidence of many observational epidemiological studies has been enough to prove that smoking causes lung cancer. But it is more challenging at this time for jurors in various Roundup trials to judge epidemiological evidence that glyphosate caused the cancer of the plaintiff. After all, jurors are not usually experts and the best trial attorneys are very persuasive in making their case.

When determining whether Roundup and glyphosate cause cancer, it should be asked whether the epidemiological studies were done properly. Second, it should be asked how objective the expert witnesses and jurors were. Science and the judicial system can get things wrong. Verdicts in trials can be wrong, and always can be appealed.

When talking about conclusively proving that Roundup causes cancer, it is worth remembering that it took years for a consensus to form regarding cancer and cigarettes. The same could hold true for glyphosate.


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