However, several studies have come out in recent years indicating that colon cancer rates are increasing in people under the age of 50.
Furthermore, "trends in young people are a bellwether for the future disease burden", Siegel said. But Siegel suggested one explanation might be a complex interaction involving the same factors that have contributed to the obesity epidemic - changes in diet, a sedentary lifestyle, excess weight and low fiber consumption.
Yet another study has found that colorectal cancer incidence rates are rising among young and middle-aged adults - two age groups that don't now undergo regular screening for the potentially fatal disease. So what age should people be screened for colorectal cancer?
Rectal cancer showed an even bigger increase of three percent per year from 1974 through 2013 in adults 20 to 29, and from 1980 to 2013 in 30- to 39-year-olds.
With screening, colon cancer can be caught early, when it's curable. Recently though, studies have reported increasing CRC incidence in adults under 50, for whom screening is not recommended for those at average risk.
The study did not uncover a reason for the change.
USA adults born in 1990 have double the risk of colon cancer and quadruple the risk of rectal cancer compared to those born in 1950-when incidence rates were the lowest-according to a study led by the American Cancer Society.
For years, overall rates of colon and rectal cancers have been dropping for the people thought to be most at risk-the elderly.
The study confirms what many doctors have been seeing among their younger patients, said Nilofer Azad, an oncologist at the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, who was not involved in the research.
"This new study would favour a closer look at whether screening should be done earlier", said Dr John Kisiel, a gastroenterologist at the Mayo Clinic in Rochester, Minnesota.
In the meantime, as they say, an ounce of prevention is worth a pound of cure - so building healthy habits while you're still young isn't just helpful to stave off disease now, but guard yourself against longterm risk for a wide variety of health conditions, including cancer.
There has been significant interest to do more research in this area, with this group of patients that we wouldn't normally expect to be diagnosed with cancer at such a young age. "But that's not what we see", she said. For people aged 40 to 54, the rates increased between.5 percent and one percent from the mid 1990s to 2013.
Conversely, in adults 55 and over, rates of rectal cancer have generally been declining for at least 40 years, even before widespread screening. But now, researchers have found that a cancer that was believed to mostly affect those over the age of 50 has been spiking in young adults.
Rates for adults older than 55 has been declining for about 40 years, researchers said.