Some research has linked lifestyle and dietary changes to increased rates of colorectal cancer in both young people and older adults. Recent generations have consumed more red meat, ultraprocessed foods and sugary beverages, and have been known to binge drink more frequently; between 1992 and 1998, cigarette smoking also increased before declining again, while physical activity has continuously declined for decades. All of these factors — along with the rise in obesity rates since the 1980s — are associated with cancer risk. But once again, none of them fully account for the increase in early-onset colorectal cancer.
“For a lot of these risk factors, like smoking, you have to be exposed for long periods of time before the cancer develops,” said Dr. Andrea Cercek, a co-director of the Center for Young Onset Colorectal and Gastrointestinal Cancers at Memorial Sloan Kettering Cancer Center. And many patients in their 20s and 30s do not even fit in these risk groups, she said. “Many of our patients are athletes,” she said. “Many of them were never heavy, not even in childhood.”
Experts are beginning to investigate if there are other environmental drivers of early-onset cancer. For instance, some small studies have hinted at the idea that people who develop colorectal cancer at an early age have an imbalance of “good” and “bad” bacteria in their gut. Researchers are not only looking at antibiotic use, which can alter the gut microbiome, but also nonsteroidal anti-inflammatory drugs that are used as painkillers, proton pump inhibitors that are used to counter stomach acid issues and several psychiatric medications that may be absorbed through the intestinal lining and have increased in use in recent decades, Dr. Cercek said.
Some experts believe exposure to toxic chemicals in the environment may also be to blame. “There’s patterns of environmental exposures by geography, by race, by sex, by all the things that we know colorectal cancer rates also differ by,” Dr. Murphy said.
For instance, for many years, the rates of colorectal cancer diagnoses were highest among non-Hispanic Black people, but research shows that these cancers increased more among non-Hispanic white people in the 1990s and early 2000s, Dr. Murphy said. Now, both groups have fairly similar rates of cancer. “Does this mean that white people are now being exposed to something that Black people have been exposed to for many, many years? We just don’t know yet,” Dr. Murphy said.
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