Colorectal Cancer Is Getting More Common In Young Adults. Doctors Don't Know Why

Signs of colorectal cancer sometimes begin with diarrhea, abdominal cramps, or unexplained weight loss, according to the Centers for Disease Control and Prevention. Although people over 50 are recommended to begin screening for colorectal cancer, a 2021 statement from the U.S. Preventive Services Task Force recommended colorectal cancer screenings begin at age 45. 

According to a 2023 article in CA: A Cancer Journal for Clinicians, colorectal cancer cases had been on the decline since the early 2000s, but that decline had slowed due to an increase of cases among people younger than 55. The proportion of colorectal cancer diagnoses among people younger than 55 has sharply increased, accounting for 20% of cases in 2019. As a whole, colorectal cancer cases are decreasing, but more people are being diagnosed with this condition much younger.

A 2021 article in JAMA Network Open projected that by 2040, colorectal cancer will be the leading cause of cancer death in the 20 to 49 age group. A 2023 article in Science says when people in this age demographic are diagnosed, their cancer is often in an advanced stage. What's causing this rise? Researchers are stumped.

Researchers are looking a little closer at the many risk factors that point to colorectal cancer (via Science). Some point to childhood and adolescent obesity combined with lack of exercise as associated with an increased risk of early-onset colorectal cancer. Hypertension, hyperglycemia, and type 2 diabetes are also connected to this cancer. An unhealthful diet high in sugary drinks and red and processed meats may also play a role. Environmental toxins and increased use of antibiotics can also factor in the increasing cases of colorectal cancer in people under 50.

Rebecca Siegel is the senior scientific director for cancer surveillance research at the American Cancer Society. She's also the lead author of the 2023 article in CA: A Cancer Journal for Clinicians. "We know rates are increasing in young people, but it's alarming to see how rapidly the whole patient population is shifting younger, despite shrinking numbers in the overall population," Siegel said in a news release. "The trend toward more advanced disease in people of all ages is also surprising and should motivate everyone 45 and older to get screened."

According to a 2021 article in JAMA Network Open, colorectal cancer cases and deaths had been declining overall because more people are getting screened. In 1987, just 35% of people over 50 were getting screened for colorectal cancer, but that number jumped to 66% by 2010. The National Cancer Institute says that regular colorectal cancer screenings can detect abnormal tissues before you have symptoms. These screenings include a fecal occult blood test, sigmoidoscopy, colonoscopy, virtual colonoscopy, or DNA stool test.

Several colorectal cancer risk factors such as age, a family or personal history, genetic links, or race can't be controlled, but giving up alcohol (or drinking in moderation), quitting smoking, and keeping a healthy weight are factors you can control, according to the National Cancer Institute. You can protect yourself from colorectal cancer by incorporating (or maintaining) physical activity into your lifestyle. The research is still unclear about how a healthy diet might protect you from colorectal cancer specifically, but the American Cancer Society recommends a diet rich in fruits, vegetables, and whole grains to prevent cancer. It also suggests limiting red and processed meats, sugary drinks, and highly processed foods.