Researchers from the American Cancer Society found a significant uptick in the number of young and middle-aged Americans diagnosed with colorectal cancer, attributed to lifestyle factors such as obesity and sedentary lifestyles. Published in the Journal of the National Cancer Institute, the authors concluded the risk of colorectal cancer for young adults today is the same as it was in 1890.

Colorectal cancer (CRC) rates have been declining in the United States for nearly 40 years, with an accelerated decline from 2003 to 2013 associated with stronger screening efficacy. However, breaking the population into age-based cohorts revealed a different story: from the mid-1980s, rates declined in adults over 55, but increased by 2.4 percent per year in adults between 20 and 29 years old and by 1 percent per year for adults between 30 and 39 years old. This spike continued into the 1990s, when rates of CRC diagnoses for adults between 40 and 49 years old and 50 to 54 also increased.

“As a consequence of these oppositional trends, the probability of a rectal cancer diagnosis for someone in their early 50s is now the same as it is for someone in their late 50s, whereas two decades ago it was just half,” wrote Siegal et al.

The authors pointed to obesity rates as a primary driver of the increase. While young adults’ declining levels of smoking and alcohol use are steps in the right direction, causes of obesity like poor diet and sedentary lifestyle can have synergistic effects when promoting the development of CRC, according to the authors.

“Evolving research suggests that specific, unhealthy dietary elements, like high–glycemic load carbohydrates, may trigger a cascade of detrimental health effects beyond caloric content. A recent study found that de novo introduction of a Western-style high-fat, low-fiber diet initiates inflammation and proliferation in the colonic mucosa within two weeks,” they wrote. “These findings are consistent with the one-generation jump in CRC risk that has been observed among Japanese migrants to the United States that is attributed to diet,” referring to a 1999 study from the University of Hawaii.

With this knowledge in hand, both the public and physicians need to take action to mitigate this rise of CRC incidence. Educating patients about their risks begins with educating their doctors, who can help impart the significance of the risk onto young adults. However, putting colon cancer on the radar of millennials may have a limited effect: They are three times as likely as adults over 55 to be uninsured. The ACA has increased detection rates for other cancers by reducing financial barriers to screening and providing insurance to more Americans, but repeal, which is a looming threat, could ameliorate those gains.

“These results highlight the need for etiologic research to elucidate causes for the underlying increase in disease risk in young birth cohorts, as well as creative new strategies to curb the obesity epidemic and shift Americans toward healthier eating and more active lifestyles,” wrote Siegel et al.