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News — Over the past three decades, rates of colon and rectal cancers—collectively known as colorectal cancer—have steadily risen among people under the age of 50. It’s particularly striking because rates have been declining among older people during the same time period. 

Even worse, young people tend to be diagnosed at later stages of the disease, making it harder to cure.

“In past years, we’ve thought of colorectal cancer as a disease of aging,” said , a gastroenterologist and Senior Scientist at the (HNRCA) at Tufts. “If you look at the absolute incidence rates, it’s still higher amongst older people, but the rate is going up steadily in young people, whereas it’s going down in older people. It’s a disturbing trend.”

Even within the under-50 age group, the trend is most pronounced in younger age groups. “The rate at which colorectal cancer is increasing is higher in the 20-somethings and 30-somethings,” said Mason, who is also the leader of the Vitamins and Carcinogenesis Team at the HNRCA and a professor at and the .

What’s Behind the Rising Rates?

Mason said that the rates are rising too quickly to be attributed to genetic changes. “It seems most likely to be an environmental factor or combination of factors,” he said, “but we can really only speculate at this point.”

The obesity epidemic may be partly to blame, because having excess body fat is associated with a higher risk of being diagnosed with colorectal cancer. 

Mason said declining rates among older people may be due to effective screening and an increased awareness of protective lifestyle factors like a healthy diet and regular exercise.

Reducing the Risk

For those looking to reduce their risk of colorectal cancer, Mason said studies have consistently found that a healthy diet and exercising at least three times a week are associated with lower rates, while being overweight and smoking are associated with higher rates.

“Among all the common cancers,” Mason said, “colorectal cancer is one where the risk is most sensitive to dietary factors.” Over the past few decades, multiple studies have shown that colorectal cancer risk can be reduced with a diet that contains plenty of fruits, vegetables, and fiber, and , red meat, and alcohol. Processed meat includes bacon, sausage, ham, hot dogs, and luncheon meat. 

There is evidence that daily aspirin can reduce the risk of developing colorectal cancer, but Mason cautioned that an aspirin regimen increases the chances of certain adverse events, such as gastrointestinal bleeding. “The major policy-making societies do not recommend daily intake of aspirin because, on balance, in people of average risk of colorectal cancer, the risk of developing adverse side effects from aspirin outweigh the potential benefits in terms of prevention,” he said.

New Screening Guidelines

In light of the rising rates in young people, the U.S. Preventive Services Task Force changed its guidelines to recommend that screening for colorectal cancer should begin instead of age 50 for people at average risk.

People whose parents or siblings had colorectal cancer before the age of 55 are at increased risk and should considered getting screened before 45.

For most people, screening consists of a colonoscopy every 10 years. If pre-cancerous polyps are found in the colon, they will be removed during the procedure. Those with polyps should follow up with another colonoscopy in five years (or less, depending on the nature of the polyps) rather than 10.

Other screening options are stool-based kits, but Mason said a positive result would still need to be confirmed by a colonoscopy, leading to delays in diagnosis. “The colonoscopy continues to be the gold standard for screening,” he said. 

Symptoms to Watch For

Some common symptoms of colorectal cancer are rectal bleeding, iron-deficiency anemia, and a distinct change in bowel habits. All of these symptoms also can be caused by other less dire conditions, such as hemorrhoids, menstrual bleeding, and food sensitivities. 

In light of rising rates of colorectal cancer in young people, Mason said providers and patients shouldn’t be too quick to attribute rectal bleeding to hemorrhoids or iron-deficiency anemia to menstrual bleeding.

“I hate to raise the anxiety level of younger people,” he said, “but the trends are very disturbing and in balance maybe it is worth making our younger population a little more vigilant about symptoms that need to be paid attention to.”