Rates of colorectal cancer are rising sharply among younger adults in the United States, and researchers now believe a toxin produced by gut bacteria may be a contributing factor. A team from the University of California, San Diego, has identified a link between colibactin – a compound secreted by certain strains of E. coli – and an increased risk of the disease in people under 50.
Colibactin can damage the DNA of colon cells, leaving a distinctive genetic imprint. Professor Ludmil Alexandrov, a member of the Moores Cancer Center at U.C. San Diego, said: “We’ve found that colibactin is one of those [substances] that can leave a mark on our genome. Its genetic imprint appears to be strongly associated with colorectal cancers in young adults.”
Colorectal cancer is now the second most common cause of cancer deaths in the U.S., with more than 158,000 new cases and 55,000 deaths expected this year, according to the American Cancer Society. However, not everyone carrying colibactin-producing bacteria develops cancer, and the condition is less common in Africa and Asia than in Western nations.
Researchers are still trying to understand why some people are affected and others are not. Microbiome expert Christian Jobin of the University of Florida noted that diet, inflammation, and medication could influence the activity of these harmful bacteria. He also suggested that early-life factors such as mode of birth, breastfeeding, antibiotic use, and exposure to ultraprocessed foods might play a role.
Experts emphasise the importance of maintaining a healthy gut from infancy. Breastfeeding, skin-to-skin contact, and avoiding unnecessary antibiotics can help build a robust microbiome. For adults, consuming probiotic-rich foods like yogurt, sauerkraut, and sourdough bread, as well as anti-inflammatory fibre from vegetables and oats, may help reduce colibactin-producing bacteria. Staying hydrated and exercising regularly are also recommended to support gut health.
