Colorectal cancer has long been considered a disease of older adults, but that picture is changing rapidly. Rates among people under 50 have been climbing at approximately 1.4% per year, and today roughly 1 in 5 colorectal cancer diagnoses occur in individuals under the age of 55. More alarmingly, colorectal cancer has now become the leading cancer-related cause of death among both men and women under 50 in the United States.
While poor diet, sedentary lifestyles, and gut microbiome disruption have long been implicated, a striking new study published in Nature Medicine in April 2026 points to another potential contributor: a widely used agricultural herbicide called picloram.
What the New Research Found
Researchers at the Vall d’Hebron Institute of Oncology (VHIO) in Barcelona analyzed DNA methylation patterns in colorectal cancer patients diagnosed both before and after age 50. These epigenetic “fingerprints” — chemical modifications that regulate how genes are expressed — can reflect a person’s cumulative lifetime exposure to environmental factors without directly measuring those exposures.
By constructing epigenetic risk scores, the team identified several factors associated with early-onset colorectal cancer. Among the most notable new findings was an association with picloram, an herbicide widely applied to control broadleaf weeds in grain crops, rangeland, and pastureland across the United States.
When the VHIO researchers cross-referenced their findings with U.S. county-level pesticide use data, counties with higher picloram application rates showed elevated rates of early-onset colorectal cancer — even after controlling for socioeconomic differences. Notably, picloram showed a stronger correlation with early-onset cases than glyphosate, the herbicide that has attracted far more public and regulatory attention in recent years.
“Both analyses are observational, so further research is necessary,” cautioned lead researcher José Seoane, PhD, Head of the Computational Biology Group at VHIO. The study establishes association — not definitive causation — and the research team emphasizes that environmental exposure is just one piece of a complex puzzle.
What Is Picloram?
Picloram is a pyridine-based herbicide registered for use across the United States and dozens of other countries. It is applied broadly to control invasive broadleaf weeds in agricultural fields, forests, roadsides, and grazing land. Unlike glyphosate, picloram has attracted comparatively little public scrutiny despite its widespread agricultural footprint.
Picloram persists in soil and water longer than many other herbicides, raising questions about cumulative environmental and dietary exposure — particularly for people who live near or work in agricultural areas where the chemical is routinely applied.
The Epigenetic Connection: Why Past Exposures Leave Lasting Marks
The mechanism through which environmental exposures like pesticides may influence cancer risk is increasingly understood through epigenetics — changes to gene expression that don’t alter the underlying DNA sequence but can persist for years or even decades.
Separately, researchers at the Broad Institute of MIT and Harvard published findings in Nature in March 2026 showing that chronic gut inflammation leaves lasting epigenetic marks on colonic stem cells, dramatically accelerating colorectal cancer development even after the inflammation itself resolves. Together, these two studies suggest a picture where environmental insults — whether from chemical exposures or persistent gut inflammation — may prime cells for malignant transformation through durable epigenetic changes that outlast the original trigger.
Research suggests these epigenetic modifications can accumulate across a lifetime, which could help explain why colorectal cancer risk doesn’t simply disappear once an exposure or inflammatory episode ends.
Other Risk Factors for Early-Onset Colorectal Cancer
The VHIO study also confirmed the role of two well-established contributors to early-onset colorectal cancer:
- Tobacco use: Smoking remains one of the most consistent modifiable risk factors for colorectal cancer across age groups.
- Dietary patterns: Diets high in processed and red meats and low in dietary fiber are strongly associated with elevated colorectal cancer risk.
Other recognized risk factors include:
- Sedentary lifestyle and excess body weight
- Heavy alcohol consumption
- A family history of colorectal polyps or cancer
- Inflammatory bowel conditions, including Crohn’s disease and ulcerative colitis
- Disrupted gut microbiome diversity
What This Means for Prevention
While more research is needed to establish a direct causal link between picloram and colorectal cancer, there are several practical, evidence-based steps that may help reduce overall colorectal cancer risk.
Eat More Fiber From Whole Foods
Studies consistently indicate that diets high in dietary fiber — particularly from vegetables, legumes, and whole grains — are associated with lower colorectal cancer risk. Fiber feeds beneficial gut bacteria, reduces the transit time of potential carcinogens through the colon, and supports a healthier gut environment overall.
Consider Organic Produce for High-Pesticide Crops
For those concerned about pesticide exposure, research suggests that organic produce carries significantly lower pesticide residue levels. Prioritizing organic choices for crops that are most heavily treated — the Environmental Working Group publishes an annual “Dirty Dozen” list as a reference — may help reduce cumulative dietary exposure over time.
Wash Produce Thoroughly
Studies indicate that washing fruits and vegetables under running water can reduce surface pesticide residues meaningfully, though this approach is less effective for systemic pesticides that penetrate produce tissue.
Don’t Delay Colorectal Cancer Screening
Current U.S. guidelines recommend beginning colorectal cancer screening at age 45. For individuals with a family history of colorectal cancer, inflammatory bowel disease, or other risk factors, consult your healthcare provider about earlier or more frequent screening. Detecting precancerous polyps before they develop into cancer dramatically improves outcomes.
Address Chronic Gut Inflammation
Given growing evidence linking chronic gut inflammation to colorectal cancer risk via epigenetic changes, maintaining gut health through a balanced diet, stress management, and appropriate treatment of inflammatory bowel conditions appears increasingly important for long-term prevention.
The Bigger Picture
The VHIO study adds to a growing body of evidence suggesting that the sharp rise in early-onset colorectal cancer cannot be fully explained by genetics or individual lifestyle choices alone. Environmental exposures — from food, water, and agricultural chemicals in our surroundings — are increasingly recognized as population-level contributors to cancer risk.
As public health researchers continue investigating which chemicals and exposure pathways carry the greatest risk, these findings serve as a reminder that cancer prevention is both a personal and a systemic challenge. Individual dietary choices matter, but so does understanding the broader environmental context in which we eat, work, and live.
If you are under 50 and experience unexplained gastrointestinal symptoms — such as rectal bleeding, persistent changes in bowel habits, or unexplained weight loss — consult your healthcare provider promptly. Early detection saves lives.
Disclosure: This content is for informational purposes only and is not medical advice. Always consult a qualified healthcare provider before making changes to your health regimen.