The rise in colorectal cancer among young people is a “global phenomenon,” according to a new study. While the increase in the number of Americans under 50 being diagnosed with the disease has been reported for a few years, new research published on Dec. 11 in the journal the Lancet Oncology demonstrates how the pattern is spreading beyond the U.S. and other wealthy Western nations. Wealth itself may be a critical factor to the rising rates of colorectal cancer, experts say. Here’s what to know about increasing disease rates among young people and the best ways to protect yourself.

What the new study found

Rates of colorectal cancer diagnosed in people between ages 25 and 49 rose over the past 10 years in 27 out of 50 countries that American Cancer Society researchers gathered data on. The sharpest increases occurred in New Zealand, Chile, Puerto Rico and England. In the U.S., where more than 20,000 under-50s are diagnosed each year, the number of early-onset cases is rising by 2.13% per year, the study found.

Although the increase is nearly twice as sharp in New Zealand — where cases are rising by 3.97% a year — what stands out about the trend in the U.S. is that cases continue to rise among young people, even as they fall among those aged 50 to 74. In addition to New Zealand and the U.S., the diverging trend can be seen in 12 other countries, including Canada, England, Germany and Scotland.

How the rise in colorectal cancers has spread with Westernization

That’s the question of the hour, or, really, of several decades. Beginning in the mid-1990s, wealthy Western nations have seen cases among young people rise while rates have fallen among older people. This first wave of this trend occurred in the U.S., Canada, Denmark, Sweden and the Netherlands. Declining rates among older people likely reflect increased screening. But in most countries, screening isn’t recommended until people are in their 40s or 50s, so cases among younger people are less likely to be caught.

In much of Latin America, the Caribbean and Asia, colorectal cancers have been climbing steadily among both younger and older people. Many of these are countries whose populations and economies have been increasing rapidly over the last 10 to 20 years, Hyuna Sung, study author and senior principal scientist at the American Cancer Society, tells Yahoo Life. “In countries that are growing, fast foods are considered a new trend,” she says. “So if you go to the growing countries, you often see people who are rich and they might be more obese, they might be drinking and they might even smoke more,” Sung says. Smoking and drinking alcohol are well-known risks for several cancers, including those of the colon and rectum. While research on the effects of fast food and ultra-processed foods is ongoing, obesity and diets high in these products are prime suspects in the rise of colorectal cancers among younger people.

“The rise in early-onset colorectal cancer did appear to start in Western societies and lifestyles, and I believe that what we’re seeing now around the world is a reflection of these lifestyles, which have become more prevalent worldwide,” Dr. Marios Giannakis, an oncologist at Dana-Farber Gastrointestinal Cancer Center, tells Yahoo Life. He notes that previous research has found strong links between both obesity and what Giannakis calls the “Western, or inflammatory diet” and colorectal cancer. When previous studies have calculated how closely correlated different types of food are with inflammation, “foods that are higher in the ultra-processed components have a higher [inflammation] index, and those have also been associated with colorectal cancer,” he explains.

And that aligns with the timing of the rise in colorectal cancers among all ages, and among younger people in particular. “There is an indication that after the 50s or 60s” when highly processed foods became more prevalent in the U.S., “we started being collectively exposed to something in the environment, and obviously now we’re seeing younger and younger generations being affected,” says Giannakis. The impact of whatever this exposure may be (it’s not settled science that it’s ultra-processed foods) is likely cumulative, meaning that younger people have been encountering it consistently since childhood, so a larger accumulation of damage occurs earlier in life.

But both Giannakis and Sung are adamant that ultra-processed foods are unlikely to be the only drivers of the rise in colorectal cancers in young people. They’re most likely working in concert with increasingly sedentary lifestyles, and perhaps some other hard-to-determine environmental exposures, such as PFAS, a.k.a. forever chemicals. “When the environment we live in reduces the opportunities for exercise, the physical activity levels would be lower in industrialized environments compared to pre-industrial environments where people have to work and grow their food,” points out Sung. “All of those built environments and food environments that come with economic wealth — we think part of this increase in colorectal cancer is attributable to those changes.”

What you can do to minimize your risks

First and foremost, don’t be scared by these findings, say Sung and Giannakis. “I don’t think there’s a reason for us to be nervous, I think it’s a good opportunity for us to learn how we can improve our overall health,” says Sung. “It’s not just about cancer; if you change your behaviors to be more healthy, that will change and reduce your risk of other diseases, such as hypertension, diabetes and obesity, in the future.”

And it’s never too late, adds Giannakis. “Adjusting to a healthier lifestyle is going to be helpful whenever it’s pursued,” he says. And while rates are climbing among young people, colorectal cancer (and cancers in general) is still much more common among older people, “which means we still have time, a window of opportunity to reduce the risk of cancer in the future as young people,” says Sung. “Now is always the best time to change your behavior.”

The best behavioral changes are simple ones, says Sung: Maintain a healthy body weight, eat whole foods like fresh fruits and vegetables, reduce your consumption of ultra-processed foods, decrease your alcohol intake and quit smoking. “We calculate that about 54% of colorectal cancer is attributable to these health behaviors,” says Sung.

That said, it’s also important to watch for signs of colorectal cancer — especially for people under 45 who are not yet eligible for screening in most cases. Those include ongoing blood in your stool, black or tarry stool, thin stool and persistent abdominal pain. “When you have these symptoms, you really shouldn’t ignore them, and talk to your doctor,” about whether you should be screened, Sung says.