Now playing
01:00
Cancer: The facts
Now playing
01:10
Trouble sleeping? This may be why
Woman pointing to area on mammogram x-ray, close-up
Getty Images/File
Woman pointing to area on mammogram x-ray, close-up
Now playing
01:19
Breast cancer: Know the facts
Laboratory Fertilization Of Eggs In IVF Treatment  Stock Photo:Image ID: 155727377
Shutterstock
Laboratory Fertilization Of Eggs In IVF Treatment Stock Photo:Image ID: 155727377
Now playing
03:06
Explain it to me: Fertility
Ways to treat heartburn_00000026.jpg
Ways to treat heartburn_00000026.jpg
Now playing
02:40
Ways to treat heartburn
CNN
Now playing
02:13
Why losing weight might protect you from Covid-19
this is your brain on pain health orig_00001025.jpg
CNN
this is your brain on pain health orig_00001025.jpg
Now playing
01:39
This is your brain on pain
Now playing
01:42
Here's why you can't stop eating pizza, ice cream and chocolate chip cookies
shutterstock
Now playing
01:49
These foods aren't as healthy as you think
Americans are still too fat according to a new study from JAMA. Two in three of Americans are registering as overweight or obese.
Shutterstock
Americans are still too fat according to a new study from JAMA. Two in three of Americans are registering as overweight or obese.
Now playing
01:15
What is obesity?
CNN
Now playing
01:17
Why your BMI matters
LONDON - MAY 16:  In this photo illustration a cigarette is seen burning on May 16, 2007 in London. Businesses and shops are gearing up for the introduction of the smoking ban on July 1 in England after similar bans have been introduced in Ireland, Scotland and Wales.  (Photo Illustration by Bruno Vincent/Getty Images)
Bruno Vincent/Getty Images Europe/Getty Images
LONDON - MAY 16: In this photo illustration a cigarette is seen burning on May 16, 2007 in London. Businesses and shops are gearing up for the introduction of the smoking ban on July 1 in England after similar bans have been introduced in Ireland, Scotland and Wales. (Photo Illustration by Bruno Vincent/Getty Images)
Now playing
01:07
What tobacco does to your health (2017)
Now playing
01:12
World blood pressure rises (2016)
A surgeon sitting in front of screens of a Focal One device performs a robot-assisted prostate tumorectomy using ultrasound imaging on April 10, 2014 at the Edouard Herriot hospital in Lyon, center France. Focal One is the first robotic HIFU (high intensity focused ultrasound) device dedicated to the focal approach for prostate cancer therapy. According to EDAP TMS SA, a leader in therapeutic ultrasound, it combines the three essential components to efficiently perform a focal treatment: state-of-the-art imaging to localized tumors with the use of magnetic resonance imaging (MRI) combined with real-time ultrasound, utmost precision of robotic HIFU treatment focused only on identified targeted cancer areas, and immediate feedback on treatment efficacy utilizing Contrast-Enhanced Ultrasound Imaging. AFP PHOTO / JEFF PACHOUD        (Photo credit should read JEFF PACHOUD/AFP/Getty Images)
JEFF PACHOUD/AFP/AFP/Getty Images
A surgeon sitting in front of screens of a Focal One device performs a robot-assisted prostate tumorectomy using ultrasound imaging on April 10, 2014 at the Edouard Herriot hospital in Lyon, center France. Focal One is the first robotic HIFU (high intensity focused ultrasound) device dedicated to the focal approach for prostate cancer therapy. According to EDAP TMS SA, a leader in therapeutic ultrasound, it combines the three essential components to efficiently perform a focal treatment: state-of-the-art imaging to localized tumors with the use of magnetic resonance imaging (MRI) combined with real-time ultrasound, utmost precision of robotic HIFU treatment focused only on identified targeted cancer areas, and immediate feedback on treatment efficacy utilizing Contrast-Enhanced Ultrasound Imaging. AFP PHOTO / JEFF PACHOUD (Photo credit should read JEFF PACHOUD/AFP/Getty Images)
Now playing
01:21
What is prostate cancer?
Argosy
Now playing
00:53
What is Parkinson's disease?
Now playing
01:38
How Alzheimer's destroys the brain
(CNN) —  

Glyphosate, an herbicide that remains the world’s most ubiquitous weed killer, raises the cancer risk of those exposed to it by 41%, a new analysis says.

Researchers from the University of Washington evaluated existing studies into the chemical – found in weed killers including Monsanto’s popular Roundup – and concluded that it significantly increases the risk of non-Hodgkin lymphoma (NHL), a cancer of the immune system.

“All of the meta-analyses conducted to date, including our own, consistently report the same key finding: exposure to GBHs (glyphosate-based herbicides) are associated with an increased risk of NHL,” the authors wrote in a study published in the journal Mutation Research.

The potential carcinogenic properties of glyphosate are the subject of widespread scientific debate. The US Environmental Protection Agency said in a 2017 draft risk assessment that the herbicide “is not likely to be carcinogenic to humans,” while the European Food Safety Authority maintains a similar stance. Bayer, which acquired Monsanto in 2018, said the same year that glyphosate is a “safe and efficient weed control tool.”

In 2015, however, the World Health Organization’s International Agency for Research on Cancer classified glyphosate as “probably carcinogenic to humans.” Moreover, the chemical has triggered multiple lawsuits from people who believe that exposure to the herbicide caused their non-Hodgkin’s lymphoma. In 2017, CNN reported that more than 800 people were suing Monsanto; by the following year, that figure was in the thousands.

One high-profile case against Monsanto was that of Dewayne Johnson, a former school groundskeeper diagnosed with terminal non-Hodgkin lymphoma in 2014. In August 2018, a judge ordered Monsanto to pay Johnson $289 million in damages, an award subsequently reduced to approximately $78 million after Monsanto appealed.

The authors of the University of Washington report analyzed all published studies on the impact of glyphosate on humans. Co-author and doctoral student Rachel Shaffer said in a statement: “This research provides the most up-to-date analysis of glyphosate and its link with Non-Hodgkin Lymphoma, incorporating a 2018 study of more than 54,000 people who work as licensed pesticide applicators.” The scientists also assessed studies on animals.

Focusing on data relating to people with the “highest exposure” to the herbicide, the researchers concluded that a “compelling link” exists between glyphosate exposure and a greater risk of developing non-Hodgkin lymphoma. Senior author Lianne Sheppard, professor in biostatistics and environmental and occupational health sciences, said she was “convinced” of the carcinogenic properties of the chemical.

In a statement, Bayer called the new analysis a “statistical manipulation” with “serious methodological flaws,” adding that it “provides no scientifically valid evidence that contradicts the conclusions of the extensive body of science demonstrating that glyphosate-based herbicides are not carcinogenic.”

The authors of the new study acknowledged some limitations of their analysis, noting that “only limited published data” was available. Moreover, they wrote, studies they evaluated varied in the population groups they targeted: specifically, the glyphosate exposure levels of the participants differed between reports.

The available studies also neglected to assess the impact of the “green burndown” farming method, which sees glyphosate herbicides added to crops before they are harvested. Glyphosate residue has probably increased since the introduction of this method in the mid-2000s, the researchers wrote.

Francis Martin, a biosciences professor at the University of Central Lancashire, told CNN he welcomed the University of Washington report. He called the debate over the safety of glyphosate “important,” explaining that “glyphosate is used as a general purpose herbicide so there will be exposure in the general population.”

Get CNN Health's weekly newsletter

Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.

However, he noted that the report was limited by the small number of existing studies on the subject, though he stressed that the authors were “honestly self-reflective on the limitations of the analyses.”

“[The report] highlights the need for new, well-designed and robust studies at appropriate exposure levels,” Martin said, adding, “The number of robust studies in the literature examining this question is pathetically small.”