In a study published by the American Cancer Society this month, researchers estimated that in 2023, 153,000 people in the United States would be diagnosed with colorectal cancer. Of those cases, about 13% would be among people younger than 50 — representing a 9% increase in cases in this age group since 2020.

Although new colorectal cancer diagnoses have been declining among people older than 50 since their peak in 1985, the trends for younger people are going in the wrong direction, said Dr. Steven Itzkowitz, a professor of medicine and oncological sciences at the Icahn School of Medicine at Mount Sinai in New York City.

And not only that, the authors of the study reported, but the cancers diagnosed in people younger than 50 are tending to be more aggressive.

“We’re living in a time when young people in their prime of life are getting colon cancers,” Itzkowitz said. “And unless we really talk about it, we may not have the opportunity to make as big a dent in this disease as we can.”

WHAT IS COLORECTAL CANCER AND WHO IS MOST AT RISK?

Colorectal cancer is the third most common cancer diagnosed in the United States. It starts as a polyp, or an abnormal growth, in the large intestine, which over time may become cancerous and potentially spread to other parts of the body.

Men and women have similar risks of developing the condition, and those risks increase with age. Just 5 in 100,000 people between ages 30 and 34 in the United States develop colon cancer, for example; whereas 61 in 100,000 people between 50 and 54 get it, and 136 in 100,000 people ages 70 to 74 do. Those who are Black or American Indian/Alaskan Native are most at risk, which many studies attribute to social inequalities and barriers to health care.

Having certain health conditions such as obesity or incorporating certain foods or drinks into your diet (such as alcohol or red or processed meats such as sausage, pepperoni or hot dogs) is also known to increase risk, as is a sedentary lifestyle.

SHOULD I BE WORRIED IF I’M UNDER 45? WHAT ARE THE EARLY SIGNS OF COLORECTAL CANCER?

First off, said Dr. Nancy Baxter, a colorectal surgeon and head of the Melbourne School of Population and Global Health at the University of Melbourne, the increasing rates of early-onset colorectal cancer are concerning, but the overall risk of someone younger than 50 developing colon cancer is still incredibly slim.

“I don’t want people to panic,” Baxter said. Fewer than 15 in 100,000 people between the ages of 20 and 49 had the condition diagnosed between 1998 and 2019. “Age still has the strongest influence on your risk of colorectal cancer,” she added.

That being said, you should still watch for early warning signs, which can include rectal bleeding, anemia, changes in bowel habits (such as sudden, new constipation) or any kind of abdominal pain. Younger people most commonly develop rectal bleeding as a first symptom, which doctors think may be because their cancers are more likely to occur closer to the end of the colon.

If you’re younger than 45 and have worrying symptoms, Baxter said, consult a physician right away.

WHY ARE CASES RISING AMONG YOUNGER PEOPLE?

Researchers don’t know for sure and are scrambling to answer this question, Itzkowitz said, but some shifts in risk factors have offered clues.

Climbing rates of obesity in children and adults may be one contributing factor, Itzkowitz said, with one major study published in 2022 concluding that obesity at age 20 or 30 can more than double your risk of early-onset colorectal cancer.

Binge drinking — typically defined as five or more drinks for men in about two hours, and four or more for women — has also been suggested as a possible driver. The practice has steadily been increasing among adults 30 and younger for decades.

But there is probably far more to the story than this, Baxter said. Researchers still don’t understand how childhood risk factors — such as having been born via cesarean section, having used antibiotics or having certain environmental exposures — may influence the risk of early-onset colorectal cancer, or what role the microbiome may play.

Sugary beverage consumption, for instance, which rose among teenagers in the 1980s and 1990s, has been linked with an increased risk of early occurrences of the condition. But it is unclear if that is because of the sugary beverages themselves, or related factors such as diabetes or any changes the sugary beverages may have made to the bacteria in our guts.

To understand why colorectal cancer rates are rising among younger people and to prevent that trend from continuing, Baxter said, we must answer these types of questions.

WHY DO COLORECTAL CANCERS IN YOUNG PEOPLE TEND TO BE MORE AGGRESSIVE?

One prevailing theory is that because young people are less likely to develop colorectal cancer than older people in the first place, they and their doctors may be less likely to notice early symptoms, leading to later diagnoses.

“I’ve definitely seen younger people who have been bounced from emergency room to emergency room until someone finally said, ‘Maybe this is something more concerning,’” Baxter said.

A study published in 2017 in the journal Clinical Gastroenterology and Hepatology, for instance, found that people younger than 50 tended to wait about two months longer than those older than 50 to get medical attention after first noticing their symptoms. Baxter said she thinks this window of time may pose an opportunity for the cancer to progress, although she noted that once younger people do seek medical care, the time to treatment is comparable to that of older adults.

But, Baxter added, the answer to why these cancers seem to grow more quickly could lie in their fundamental biology. “The cancers that affect younger people are more likely to be inherently aggressive,” she said. Scientists have found that early-onset colorectal cancers have different molecular, epigenetic and genetic characteristics than those diagnosed later in life. These differences could be contributing to why these cancers are more advanced when diagnosed.

WHAT CAN I DO TO LOWER MY RISK OF COLORECTAL CANCER?

Itzkowitz said that people younger than 45 should have frank discussions with their relatives about their family’s medical history.

“People either don’t take the time to find their family history, or their family members are embarrassed to talk about it, but it’s one easy thing that anyone at any age can do,” he said.

If you have a first-degree relative (such as a parent or a sibling) who had colorectal cancer diagnosed before age 60, or if you have two first-degree relatives diagnosed at any age, then you are at higher risk.

Although you can’t change your family history, of course, there are some lifestyle tweaks you can make to reduce your risk, including:

Following a healthy diet. Diets high in processed meats (such as hot dogs, bacon and some lunch meats) or red meats (such as beef, pork and lamb) have been shown to increase the risk of colorectal cancer; those rich in fruits, vegetables and whole grains have been shown to be protective. Even small changes, such as choosing fiber-rich fruits and vegetables as snacks over chips, or incorporating “meatless Mondays” into your weekly meal plan, can make a difference.

Quitting smoking. More than 70 chemicals in cigarettes are known to increase the risk of cancer by damaging the DNA inside our cells. Nicotine patches, gums and lozenges can help curb cravings, according to the Centers for Disease Control and Prevention. And many free smartphone apps, such as the quitSTART app, can offer tips, motivation and challenges to help you quit smoking.

Staying active. In one study of nearly 90,000 female nurses published in 2018, researchers found that those who were sedentary and watched TV more than 14 hours per week were significantly more likely to develop early-onset colorectal cancer than those who watched TV fewer than seven hours per week. Federal guidelines recommend that every week, most adults get at least 150 minutes of moderate-intensity activity (such as cycling, swimming or gardening) and two days of muscle-strengthening activities (such as lifting weights or pushups).

Cutting back on alcohol. Excessive alcohol drinking (such as 14 or more drinks per week, according to one study published in 2012) can increase the risk of developing early-onset colorectal cancer. Federal guidelines recommend limiting your intake to no more than one drink per day for women and no more than two drinks per day for men.

Maintaining a healthy weight. Although the body mass index is an imperfect measure of health, researchers have found that those who have a BMI under 25 are at lower risk of developing early-onset colorectal cancer. If you’ve been struggling with your weight, it’s worth chatting with your doctor. Several approved medications for weight loss, such as phentermine or liraglutide, are now recommended for adults with obesity.

Getting screened. Experts recommend that most people start screening with a colonoscopy — or a similar procedure called a flexible sigmoidoscopy — at age 45. If you have a family history, or if you are genetically predisposed to cancer as with Lynch syndrome or if you have an inflammatory bowel disease such as ulcerative colitis, your doctor may recommend that you start screening before age 45. In such cases, early screenings should be covered by insurance.

If you don’t have these risk factors, your insurance may cover colonoscopy only if you have certain symptoms, such as rectal bleeding.

According to a recent American Cancer Society study, 4 in 10 Americans ages 45 years and older were not up to date on colorectal cancer screening in 2021, and among those between 45 and 49, only 20% were up to date. “Some people say it’s the most preventable, but least prevented cancer that we deal with,” Itzkowitz said.

Ultimately, the best screening test for younger people is the one that gets done, he said. Talk with your physician about the pros and cons of each one to make the decision that’s right for you.

This article originally appeared in The New York Times.