Data show more Millennials and Gen Zers get colon cancer: Is obesity why?

Fresh data from the American Cancer Society show colon cancer is now the leading cause of cancer deaths in men under the age of 50. Among women under age 50, colon cancer is second only to breast cancer. Not so long ago, colon cancer ranked fourth in that age group.

While the numbers of cases are still relatively small, looking at those statistics, the question practically jumps out of the page: What the heck is going on? We don't yet have a clear answer. But a raft of plausible theories must be aggressively investigated. And in the meantime, we should focus on what can be done to reverse this worrisome trend.

The rising rate of early-onset cancer is occurring most prominently in the colon, although doctors also note subtle increases in tumors of the appendix, bile duct and pancreas. Those locations indicate a list of possible culprits, from the sudden rise in obesity to our sedentary lifestyle to the introduction of processed food. But researchers just don't know.

So far, most of what we know is what's not happening. There doesn't seem to be a rise in genetically linked cancer. While younger colon cancer patients have certain distinct characteristics—just over half go to their doctor because they have rectal bleeding and their tumors are more often on the left side—their cancers seem to have the same rate of mutations as cancers occurring in older people.

Unraveling what's driving the increased rates of colon cancer in younger people is a gargantuan task. It requires considering the major behavioral, lifestyle and environmental changes that occurred as cancer rates rose, seemingly starting with people born in the late 1970s and early 1980s.

Researchers will have sift through everything that could influence someone's health: their dietary habits, whether they were breastfed, how often they took antibiotics as a child, what other medicines they've taken—the list goes on.

"I can't even remember what I had for dinner last night, and we're asking people to remember what they ate when they were 5 years old," says Christopher Lieu, co-director of GI Medical Oncology at the University of Colorado Cancer Center. Researchers can try to mine data from previous longitudinal studies, such as the Nurses' Health Study, but that still can have limitations. It will take years to untangle the various risk factors.

Rates of obesity in the US began their precipitous rise during the mid-1970s and early 1980s, so that's one obvious suspect. Studies show that obesity is a risk factor for colon cancer in general, and for early-onset colon cancer among women.

Researchers attribute rising obesity rates in the UK to a predicted 39% increase in colorectal cancer deaths among women under the age of 50, compared to 2019 levels. But it's still unclear whether the extra weight is what's causing these earlier tumors or just correlated with them. In fact, specialists who treat these early-onset patients say they often see people who aren't overweight—in fact, some are training for marathons or eating plant-based diets when their symptoms appear.

The gut microbiome—the complex network of bacteria, fungi and viruses that help us digest food—is also of particular interest. A growing body of research suggests that people with early-onset colon cancer have differences in the composition of microbes residing in their intestines, as well as differences in how those bugs interact with their host.

Even if we never find a single smoking gun to explain the rise in early cancers, we ought to be able establish an evidence-backed list of risk factors. Ideally, some of those would include lifestyle choices that individuals can modify. And such a list would also allow doctors to flag high-risk patients for regular screening at a younger age.

But even without that list of risk factors, there are a few things younger adults can do to feel more in control of their health. Some are the obvious lifestyle changes that can lower your risk of all diseases, including cancer—things like eating more fruits, vegetables and fiber, exercising regularly, maintaining a lower body weight, taking a moderate approach to drinking and eschewing tobacco altogether.

Being proactive about routine care is also critical. When detected early, colon cancer is highly treatable, but too often, younger patients are being diagnosed with later-stage disease. That's in part because they often ignore symptoms (younger patients often experience abdominal pain, rectal bleeding, anemia or diarrhea) and when they do seek help, those symptoms aren't taken seriously.

Having a primary care doctor might improve those stats. A 2018 poll from KFF found that 45% of adults under the age of 30 and nearly a third in their 30s and 40s lacked a regular doctor, because, well, they're young and healthy. But a steady relationship with a doctor makes patients more able to detect a change in symptoms and identify a problem early, Lieu says.

Although the recommended age for colon cancer screening was recently lowered to 45 from 50, doctors aren't advocating lowering that age further. They instead emphasize that anyone experiencing symptoms should bring them to their doctor—and follow up on suggested tests, even if that can feel daunting. "Just do something," says Nancy You, leader of the Young-Onset Colorectal Program at MD Anderson. "If it's too scary to book a colonoscopy, just do a stool test. Something is better than nothing."

Awareness of the growing problem should prompt people under 50 to pay closer attention to the signals from their bodies—and seek out help early, when colon cancer is still very treatable.

2024 Bloomberg L.P. Distributed by Tribune Content Agency, LLC.