NAIROBI, Kenya – An international study has uncovered a possible connection between early-life exposure to a common strain of E. coli and the rising incidence of colorectal cancer among people under 50.
Long seen as a condition affecting older adults, colorectal cancer is now increasingly striking individuals in their 20s, 30s, and 40s—especially in Western nations such as the United States and the United Kingdom.
Scientists believe a bacterial toxin may be a key piece of the puzzle.
Researchers at the University of California, San Diego, analyzed tumor DNA from nearly 1,000 patients across 11 countries.
They discovered that a DNA-damaging toxin called colibactin, produced by specific strains of E. coli, was significantly more prevalent in tumors of patients under the age of 40.
“Early-life events might play a far greater role than previously understood,” said Dr. Ludmil Alexandrov, senior author of the study published in Nature. “These mutations are like a genetic record, pointing to damage that likely began before age 10.”
Colibactin-producing bacteria are commonly contracted in childhood through contaminated food or water.
Undercooked meat, unpasteurized dairy, and raw produce—especially leafy greens, sprouts, and cucumbers—are frequent sources of exposure, often due to polluted irrigation or contact with animal waste.
The study estimates that up to 40% of children in the U.S. and U.K. may host these strains, potentially setting the stage for cancer decades later.
Notably, the mutation patterns associated with colibactin were most common in countries experiencing the highest rates of early-onset colorectal cancer.
In addition to bacterial exposure, researchers point to lifestyle and medical trends such as rising rates of cesarean sections, widespread childhood antibiotic use, and the growing consumption of ultra-processed foods as possible contributors to the problem.
With colorectal cancer projected to become the leading cause of cancer-related deaths among young adults by 2030, scientists are calling for urgent action.
The findings underscore the importance of exploring microbial and environmental influences on cancer risk and open the door to new preventive strategies—such as targeted probiotics that could suppress harmful gut bacteria.
