5 Reasons Why Colorectal Cancer May Be Rising in Young Adults

Colorectal cancer (CRC) was once considered a disease of older adults, but that assumption is no longer safe.¹ In 2023 alone, nearly 20,000 children, adolescents, and adults younger than 50 years were diagnosed with CRC—part of a troubling and persistent trend that has seen rates in this age group climb by about 3% per year since the early 2010s.

What’s fueling this shift? Here are 5 key reasons why CRC may be rising in young adults—and why it’s time to rethink how we screen, educate, and intervene for the next generation.

1. Dietary Patterns and Ultra-Processed Foods

A growing body of research suggests that diet plays a significant role in the development of early-onset colorectal cancer (EOCRC) and precancerous colorectal adenomas in young adults.² A recent systematic review published in Frontiers in Nutrition identified 10 studies linking dietary patterns to EOCRC risk, finding that high intake of sugary drinks, fried and refined foods, and pro-inflammatory or Western-style diets was associated with increased incidence. In contrast, adherence to healthier eating patterns—such as the Prudent diet, Mediterranean diet, or Dietary Approaches to Stop Hypertension diet—along with higher intake of fruits, vegetables, fiber, and micronutrients, appeared to offer a protective effect.

2. Rising Rates of Obesity and Sedentary Lifestyles

In an increasingly screen-based and automated world, sedentary behavior has become a near-universal feature of daily life.³ A comprehensive meta-analysis published in the British Journal of Cancer of 23 studies involving more than 4.3 million participants found that prolonged sedentary behavior is significantly associated with a higher risk of colon cancer, with individuals who sit the most facing a 30% increased risk compared with those who are more active.

Additionally, excessive screen time—particularly TV-watching—has been linked to a higher incidence of CRC in young adults, even after accounting for other factors like obesity and physical activity levels.⁴ The risk appears to increase with more hours spent watching TV. To counteract this, the American Cancer Society recommends at least 150 minutes of moderate-intensity exercise per week, along with strength training and 75 minutes of vigorous activity.

3. Gut Microbiome Disruption

The gut microbiome (GM)—a complex ecosystem of trillions of microbes—is increasingly being implicated in the rise of CRC among younger individuals.⁵ One emerging suspect is colibactin, a DNA-damaging toxin produced by certain strains of E coli and related bacteria. A recent global study published in Nature analyzing tissue from nearly 1000 patients with CRC found that younger patients, particularly those younger than 40 years, were significantly more likely to have tumors bearing colibactin-related mutations—up to 3- to 5-times more likely than older patients. Strikingly, these mutations appear to result from exposures occurring in early childhood, suggesting that microbiome disturbances during the first decade of life may set the stage for cancer decades later. Although colibactin isn't the only factor, researchers believe it's one of several "hits" to the microbiome—possibly triggered by environmental exposures like antibiotics, inflammation, or ultra-processed foods—that collectively accelerate cancer risk.

4. Delayed Diagnosis and Lack of Screening

As CRC continues to rise among individuals younger than 50 years, early detection is becoming a critical public health priority.⁶ A large community-based study from Taiwan, published in JAMA Oncology, found that initiating fecal immunochemical test (FIT) screening between ages 40 and 49 years—rather than waiting until age 50—led to a 39% reduction in CRC mortality and a 21% reduction in incidence. Although current US guidelines recommend starting at 45 years for average-risk adults, many younger individuals with symptoms or risk factors still face barriers to affordable and timely screening. Incorporating low-cost, noninvasive tools like FIT into earlier preventive care—especially for those with a family history or persistent symptoms—could help shift CRC detection to earlier, more treatable stages and ultimately reduce the burden of disease in younger generations.

5. Environmental and Epigenetic Factors

The rising incidence of EOCRC appears to be shaped in part by cumulative environmental exposures that have accelerated since the mid-20th century.⁷ Research published in Heliyon suggests that individuals born after 1950 may face heightened EOCRC risk due to increased contact with environmental pollutants, endocrine-disrupting chemicals (EDCs), and climate-related changes—all of which can disturb the GM, a key regulator of immune function and inflammation. Particulate matter from air pollution and EDCs, commonly found in plastics, pesticides, and personal care products, can alter gut bacterial composition, trigger chronic inflammation, and promote oxidative stress—all factors that contribute to cancer development.

Additionally, climate change may indirectly influence GM by altering food systems, increasing heat stress, and shifting pathogen exposure. These disruptions can push the gut into a state of dysbiosis, potentially increasing susceptibility to CRC at earlier ages.

References

1. Reese J. Contributor: An urgent call to action as colorectal cancer rates skyrocket among young people. AJMC^®. November 4, 2025. Accessed June 27, 2025. https://www.ajmc.com/view/contributor-an-urgent-call-to-action-as-colorectal-cancer-rates-skyrocket-among-young-people

2. Carroll KL, Fruge AD, Heslin MJ, et al. Diet as a risk factor for early-onset colorectal adenoma and carcinoma: A systematic review. Frontiers. June 8, 2022. Accessed June 27, 2025. https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2022.896330/full

3. Cong YJ, Gan Y, Sun HL, et al. Association of sedentary behavior with colon and rectal cancer: A meta-analysis of observational studies. Br J Cancer. 2014 Feb 4;110(3):817-26. doi: 10.1038/bjc.2013.709

4. Lifestyle habits fuel risk of colorectal cancer in young people. ThedaCare. March 13, 2025. Accessed June 27, 2025. https://thedacare.org/lifestyle-habits-fuel-risk-of-colorectal-cancer-in-young-people

5. Stone W. Damage from gut bacteria may play a role in the rise in colon cancer in young adults. NPR. April 25, 2025. Accessed June 27, 2025. https://www.npr.org/sections/shots-health-news/2025/04/25/g-s1-62623/colon-cancer-gut-health-microbiome-young

6. Steinzor P. Starting colorectal cancer screening at age 40 cuts death risk by 39%, study finds. AJMC®. June 12, 2025. Accessed June 27, 2025. https://www.ajmc.com/view/starting-colorectal-cancer-screening-at-age-40-cuts-death-risk-by-39-study-finds

7. AlZaabi A, Younus HA, Al-Reasi HA, et al. Could environmental exposure and climate change be a key factor in the rising incidence of early onset colorectal cancer? Heliyon. 2024;10(16). doi:10.1016/j.heliyon.2024.e35935