It's a good news/bad news story. Although fewer Canadians over 50 are being diagnosed with colorectal cancer, cases among younger adults are increasing.

In a study published Wednesday in the Journal of the American Medical Association (JAMA), researchers looked at the data from all Canadians who were diagnosed with colorectal cancer between 1969 and 2015.

They found that for women under 50, there was an average increase of 4.45 per cent per year in new cases since 2010. Canadian men under 50 had an average annual increase of 3.47 per cent per from 2006 to 2015.

"I was hoping that we would see a plateau in those most recent years of cancer data, but to see that they are continuing to increase to some of the highest we've observed was surprising and alarming," said Darren Brenner, an epidemiologist from the University of Calgary and the lead author of the study.

Diet to blame?

Brenner said it's early to understand what's causing the trend.

But he and other researchers believe the most likely culprit is excess body size and obesity. He said the generation moving into their 40s and 50s are the first to experience big changes in diet, such as more processed foods, as well as foods with less fibre. Brenner said the impact of that is starting to be seen in terms of increased cancer rates in those populations that aren't normally screened.

"Our research group and a few others across the country are interested to sort of study the … factors driving risk in this population," he said.

Canadians, regardless of their age, should watch for changes in bowel movements, cancer societies say.

An international study published online in Lancet in May supported these findings. It found that colorectal cancer incidence was on the rise among young adults in several high-income countries, including Canada.

"Our findings are of concern and highlight the need for action to counteract the rising burden of disease in younger people," Marzieh Araghi from the International Agency for Research on Cancer (IARC) in Lyon, France, said in a Lancet release.

In the U.S, the American Cancer Society now recommends that screening for colorectal cancer should begin at age 45. However Brenner believes more research needs to happen before Canadian authorities make the same decision.

Listen to your body

Leah Smith, the national epidemiologist for the Canadian Cancer Society, agreed. She said the number of colorectal cancer cases is still relatively small and screening for this age group may not be worth it, in terms of effectiveness.

"About six per cent of all colorectal cancer cases are diagnosed in Canadians under the age of 50, and so population-based screening may not be the appropriate way to tackle this," she said from St. John's.

Currently, Canadian gastroenterology guidelines call for screening to begin at age 50 for those without a diagnosed parent, child or sibling.

Both Smith and Brenner believe all Canadians, regardless of their age, need to be in tune with their bodies and see a doctor if something changes. One of the early signs of colorectal cancer is blood in the stool.

"Any early sign like that is something that Canadians should act on," said Smith.

Colorectal cancer is the most commonly diagnosed cancer in Canada. It is the second leading cause of cancer death in Canada in men, and the third leading cause of death in women.