Findings of a new study may alarm young adults: while the incidence of colon cancer is declining among older people, it is increasing among young adults.

In the study published in JAMA Surgery on Nov. 5, Christina Bailey from the department of surgical oncology of the University of Texas MD Anderson Cancer Center and colleagues analyzed the data of the National Cancer Institute (NCI) covering the years 1975 to 2010 and found that the incidence of colorectal cancer has decreased by about one percent per year during the period for both men and women.

There were disparities in the rate of diagnosis when it comes to age, though. The researchers found that the prevalence of colon cancer has dropped by one percent per year in people who were at least 50 years old but diagnosis has increased by two percent annually in people between 20 to 34 years old, and nearly half a percent per year in individuals between 35 to 49 years old.

"There has been a steady decline in the incidence of colorectal cancer (CRC) in patients aged 50 years or older, but the opposite trend has been observed for young adults," the researchers wrote.

Bailey and colleagues said that if the trend continues, the incidence of colon and rectal cancer would significantly jump among young adults. By 2030, the incidence of colon cancer would rise by 90 percent among individuals between 20 and 34 years old.

People in this age group would also see an increase in rectal cancer cases by up to 124.2 percent. For those between 35 to 49 years old, the increase would be 27.7 percent for colon cancer and 46 percent for rectal cancer.

The researchers have not determined the cause of the trend, but cancer experts said that lifestyle and diet among young adults could be a factor.

"It's impossible at this juncture to determine why colorectal cancer incidence is rising among young adults, especially those ages 20 to 34," North Shore University Hospital gastroenterologist David Bernstein said. "My guess is the increase is somehow related to dietary or environmental factors, but extensive scientific research is needed to uncover the true causes."

Colorectal cancer is among the leading cancer killers in the U.S. The American Cancer Society recommends that individuals who are at least 50 years old should be screened for colon cancer every five years. The findings of the new research may push for changes to this recommendation to include young adults significantly.