Colonoscopies are a rite of passage for 50-year-olds—could that one day be true for 30-year-olds? We're not there yet, but we may be on our way. Researchers from the American Cancer Society have identified a sharp rise in colon and rectal cancer rates among millennials and GenXers after reviewing some 500,000 cases dating to 1974. How sharp? Their study, published Tuesday in the Journal of the National Cancer Institute, finds people born in 1990 have twice the risk of colon cancer and four times the risk of rectal cancer as someone born in 1950. And here's the longer view: "Colorectal cancer risk among millennials has escalated back to the level of those born" circa 1890, says lead study author Rebecca Siegel in a statement picked up by Live Science.
About 135,000 Americans are diagnosed annually with the cancers (and 50,000 die each year, reports USA Today), but those 55 and younger now make up an appreciable number of diagnoses: 29% of rectal cancer and 17% of colon cancer cases. "Colorectal cancer had been thought a success story," as increased screening tamped down overall rates, says Siegel. But what researchers found is a dichotomy between the younger and older groups. For instance, rectal cancer rates were down over the 1974 to 2013 study period for those 55 and up, but grew 3.2% annually for those ages 20 to 29. And "anything more than about 1% a year is a big change," says Siegel. The researchers didn't identify a cause, but point out a trio of risk factors: obesity, a sedentary lifestyle, and a low-fiber diet. (Read more colon cancer stories.)