• New research suggests that a common herbicide called propyzamide, often used to kill weeds, may contribute to the rising rates of inflammatory bowel disease (IBD).
  • Researchers hope the new information leads to new therapies.
  • In the meantime, experts shared steps people can take to reduce exposure to propyzamide.

Inflammatory bowel disease rates have spiked in the last decade, and new research indicates a common herbicide may be playing a role.

The study, published in Nature on October 20, suggests that a specific herbicide, propyzamide, may increase inflammation in the large and small intestines and increase the risk of developing inflammatory bowel disease (IBD).

Propyzamide is commonly used in agriculture to kill weeds.

“Our research provides a new method/platform to understand how chemicals in the environment, to which we are exposed on a daily basis, could promote the development of inflammatory disorders,” says corresponding author Francisco Quintana, PhD, an investigator in the Brigham’s Ann Romney Center for Neurologic Diseases. “[Inflammatory diseases] are an important public health problem, as those diseases are increasing worldwide.”

A CDC report published in 2021 indicated that IBD diagnosis in Medicare fee-for-service beneficiaries ages 67 and older increased across all racial and ethnic groups, with the highest annual percentage increase happening “among non-Hispanic Black persons.”

Quintana believes the new study provides a clue that may help explain why.

To conduct the study, researchers tapped into IBD genetics databases and ToxCast, the Environmental Protect Agency (EPA) database that has biochemical data regarding consumer, industrial, and agricultural products.

From there, the investigators identified multiple chemicals that might affect inflammatory pathways and tested the chemicals using a new zebrafish IBD model. They aimed to determine whether the tested chemicals would improve, exacerbate, or not affect gut inflammation.

The researchers narrowed their list to the top 20 chemicals that could influence inflammatory pathways and noted that 11 of them were used in agriculture.

They zeroed in on propyzamide, a weed killer often used on sports fields and food and vegetable crops.

Further studies suggested propyzamide disputed the aryl hydrocarbon receptor, which Quintana says plays a part in immune regulation, gut balance, and halting inflammation.

Dele Ogunseitan, PhD, MPH was not involved with the study but isn’t shocked by the results.

“Scientists are beginning to understand the wide range of environmental triggers, and it is not surprising that exposures to [herbicides], which are made to be toxic to living things, are among the most common risk factors in terms of exposures,” Ogunseitan says.

But he cautions that the study is one piece to the puzzle and more research will be challenging to pull off but is necessary.

“The methods used in the research can only produce the initial step in the association of exposure to propyzamide and inflammatory bowel disease,” Ogunseitan says. “It is difficult to produce fool-proof evidence of causality.”

What would further telling research look like?

“The next more confirmatory step would be to show that most of the people who have IBD have also been exposed to the herbicide,” Ogunseitan says. “But there are probably many other risk factors linked to IBD, and I would not be surprised if additional research reveals that many people exposed to the herbicide do not develop IBD, and many people with IBD have never been exposed to the herbicide.”

Therefore, there’s no need to panic that you’ll definitively get IBD if you’ve been exposed to propyzamide. But awareness is critical at the individual, policy-maker, and public health levels.

IBD is at the center of the study. But, as Ogunseitan said, there could be other triggers. Though the exact cause is unknown, the CDC suggests a weakened immune system and genetics may be factors.

There are two primary types of IBD, according to the CDC. Crohn’s Disease and Ulcerative Colitis. Crohn’s Disease can affect multiple layers of the GI tract, while Ulcerative Colitis occurs in the lining of the colon’s innermost layer.

And one healthcare professional says it’s important to distinguish IBD, discussed in this study, from irritable bowel syndrome (IBS) to prevent misinformation.

“IBS can be triggered by low-level food allergies and disruptions in our normal gut bacterial flora and doesn’t involve the inflammatory pathway connected with IBD,” says Claire Crunk, WHNP and Founder/CEO Trace Femcare, Inc. “IBD, linked with that inflammatory pathway, tends to have more severe and specific symptoms with significant impacts on quality of life.”

According to the CDC, IBD symptoms include:

  • fatigue
  • painful cramps
  • diarrhea
  • swelling

Crunk suggests seeing a healthcare professional if you are experiencing these symptoms.

Quintana hopes the new research adds another layer of information.

“Methods to study the contribution of the environment — the exposure — were limited,” he says. “Our study addresses that gap.”

Quintana is also hopeful the study helps develop new, targeted therapies. The research team is looking to develop nanoparticles and probiotics to target the inflammatory pathway their study suggested is affected by propyzamide exposure.

Ogunseitan stresses that issue won’t be solved without systemic change at the legislative level and recommends propyzamide be evaluated for a phase-out or ban.

“All [herbicides] that are commonly used and proven to be toxic to humans and animals should be restricted through regulatory policies,” he says.

In the meantime, what can individuals do to reduce their exposure? Knowledge, like the information the new study gave, is critical.

Ogunseitan says good hygiene, such as washing hands and rinsing fruits and vegetables before cooking with them or eating them, can help lower your exposure risk to toxic chemicals.

The experts that spoke with Healthline said that in the absence of strict regulations, it will be difficult to completely avoid exposure to propyzamide through food. However, you can lower the contact your body has with the herbicide.

They recommend trying to grow your own fruit and vegetables or buy organic, though they admit that this advice may not be feasible for everyone based on budget, living arrangements, or time constraints.