Colon Cancer Risk Before 40 May Be Linked To These Factors, Study Finds
Colon cancer used to be thought of as a disease that showed up later in life. For decades, the standard advice was to get screened at 50 and go from there. But that picture has changed.
Rates of colon cancer diagnosed before age 50 have been climbing steadily for more than two decades, and it's now the leading cause of cancer-related death in Americans under 50. And it's now recommended to get your first screening at 45. Researchers have been trying to understand why. Diet, physical inactivity, the gut microbiome have all have been linked to the trend. But new research published in Cancer points to the role of demographics and parental characteristics. Here's what you need to know.
About the study
The research comes from the California Linkage Study of Early-Onset Cancers, which connected California birth records with statewide cancer diagnosis data spanning 1988 through 2021. Researchers wanted to know whether factors recorded at the time of a person's birth (things like sex, birth weight, and parental age) were linked to their chances of developing colon cancer decades later.
The study included 1,221 people born and later diagnosed with colon cancer in California between the ages of 0 and 39, matched to more than 61,000 people without cancer. Researchers looked at a wide range of variables: the child's sex, race and ethnicity, birth weight, gestational age, birth order, and delivery method, as well as information about both parents, including age, education, and birthplace.
Even before this study, researchers have observed what's called a birth cohort effect in early-onset colon cancer, meaning people born in more recent decades face higher risk than those born earlier. This pattern is thought to be partly driven by the global spread of Western-style diets and shifting environmental exposures over time.
People with these traits have an elevated risk
After accounting for all the demographic, birth, and parental factors in the study, several stood out as meaningful.
Males had a 34% higher risk of colon cancer compared to females. Among females specifically, every additional 500 grams of birth weight was linked to a 10% higher risk. Among female offspring, having a father who was 35 or older at the time of birth was associated with a 56% higher risk.
Hispanic individuals had more than a third higher risk compared to non-Hispanic White individuals. Having a foreign-born mother was linked to a 15% lower risk, though this association was only statistically significant among males.
The study authors flag the birth weight and paternal age findings as areas that need more investigation before drawing firm conclusions.
What might explain these patterns
The study doesn't prove cause and effect, but the researchers offer some plausible explanations.
- Why males may be at higher risk: The difference may come down to sex hormones and the gut microbiome. Estrogen appears to offer some protection against colorectal cancer in premenopausal women, while higher testosterone levels have been linked to increased risk. Differences in gut microbiome composition between sexes may also play a role.
- Why Hispanic individuals face higher risk: Although colorectal cancer rates are generally lower among Hispanic individuals overall, the picture shifts with age. According to prior research cited in the study, the proportion of Hispanic individuals aged 20 to 29 with advanced-stage colorectal cancer rose from 28% to 41% between 2000 and 2016. Structural barriers to screening (including language, income, and lack of health insurance) can also lead to later diagnoses.
- Why older paternal age may matter among female offspring: Children born to older fathers may carry a higher rate of new genetic mutations, ones that arose fresh at conception rather than being inherited. Some of those mutations may influence cancer risk later in life, though the authors note this finding needs to be confirmed by future research.
- Why a foreign-born mother may be protective: Foreign-born Hispanic mothers tend to have healthier diets and lower rates of obesity during pregnancy compared to US-born mothers. Since maternal obesity has been linked to higher colorectal cancer risk in offspring, this may partly explain the protective effect.
What you can do now, even if you can't change how you were born
The risk factors identified in this study (sex, ethnicity, birth weight, paternal age) aren't things you can change. But that doesn't mean you're without options.
- Eat for your gut: A diet high in ultra-processed foods and excessive alcohol intake are among the most evidence-supported dietary risks for colorectal cancer. On the flip side, fiber and fermented foods support a healthy gut microbiome. And when it comes to modifiable cancer risk factors across cancer types broadly, diet, physical activity, and weight management consistently top the list.
- Know the warning signs: Early-onset colorectal cancer is often caught at an advanced stage, partly because younger people may not immediately think of colon cancer when symptoms appear. Watch for persistent changes in bowel habits, rectal bleeding, unexplained weight loss, and abdominal discomfort that doesn't resolve. Don't dismiss these symptoms because of your age.
- Talk to your doctor about screening: Current guidelines recommend routine colorectal cancer screening starting at age 45 for average-risk individuals. If you're Hispanic, male, or have a family history of colorectal cancer, it's worth having a proactive conversation with your doctor about whether earlier or more frequent screening makes sense for you.
The takeaway
A new study of more than 1,200 Californians with early-onset colorectal cancer found that male sex, Hispanic ethnicity, higher birth weight among females, and older paternal age may all influence colon cancer risk decades before a diagnosis ever happens.
While you can't change these circumstances, you can still offset your risk by focusing on your metabolic health.
And remebr that if something feels off, don't wait to talk to your doctor about it.