Colorectal Cancer Is Still Rising 1.7% a Year in Men, Even After Adjusting for Lifestyle

If you've watched colorectal cancer (CRC) rates climb in younger and younger adults and wondered whether it's just smoking, weight, or drinking driving the trend, a new pooled analysis of more than 224,000 Finns says: not entirely. Even after statistically adjusting for the known lifestyle risk factors, colorectal cancer incidence kept rising, and two factors researchers usually blame, education level and physical inactivity, turned out not to be statistically significant risk factors at all. For anyone tracking their own colon cancer risk or wondering what actually moves the needle, this 43-year study is one of the largest attempts yet to pull those threads apart.

Key Takeaways

• In a pooled study of 224,048 Finns followed for up to 43 years, colorectal cancer incidence rose 1.7% per year in men and 1.0% per year in women, even after adjusting for smoking, alcohol, weight, physical activity, and diabetes.
• Being tall carried a 41% higher colorectal cancer risk in men and a 24% higher risk in women (tallest vs. shortest third of the population), a well-replicated but still poorly explained association.
• Education level and physical inactivity were NOT statistically significant colorectal cancer risk factors in this study, a genuine surprise given Finland's history of higher CRC rates in higher-education groups.
• This is an observational study: no mechanism was tested, risk factors were measured only once at the start of follow-up, and the study covers only Finland.

Colorectal Cancer Incidence Keeps Climbing After Full Lifestyle Adjustment

Colorectal cancer incidence, after statistically adjusting for smoking, alcohol, body weight, physical activity, education, and diabetes, still increased by an average of 1.7% per year in men and 1.0% per year in women between 1972 and 2015, according to a pooled cohort study published in the International Journal of Cancer. The study, run by Finland's Cancer Registry and Institute for Statistical and Epidemiological Cancer Research (METCA project), combined data from seven separate Finnish health surveys, including the Helsinki Health Study and FINRISK, and linked every participant to the national cancer registry using personal identity codes. In other words, the known risk factors don't fully explain why colorectal cancer keeps becoming more common, something is still left over even once you control for the usual suspects. The rise was sharpest in one specific group: current male smokers saw colorectal cancer incidence climb 2.7% per year (95% confidence interval 1.3 to 4.1%), while incidence in never- or former-smoking men showed no comparable upward trend.

Why This Matters If You're Thinking About Your Own Colon Cancer Risk

Colorectal cancer is the third most common cancer worldwide and accounts for roughly 10% of the global cancer burden, and CRC incidence trends have been rising in many high-income countries even as other cancers stabilize or decline. This study directly measured which risk factors actually predicted a person's odds of developing colorectal cancer, not just who has the disease. Among men, current smokers had 1.40 times the colorectal cancer risk of never-smokers, obesity carried 1.42 times the risk of normal weight, and living with diabetes carried 1.36 times the risk. Among women, the standout was alcohol: heavy drinkers had 1.61 times the colorectal cancer risk of non-drinkers, while obesity carried 1.39 times the risk. Diabetes raised women's risk 1.43-fold. The sex split itself is a useful, concrete takeaway: smoking mattered more for men's colorectal cancer risk, heavy alcohol use mattered more for women's.

Seven Cohorts, 224,048 Finns, 43 Years of National Registry Linkage

The analysis pooled data from seven Finnish cohort studies spanning survey years from 1972 to 2015, covering 224,048 people, of whom 2,006 were later diagnosed with colorectal cancer (1,020 of about 100,522 men, 986 of the remaining women) via ICD-10 codes C18.0 through C20.99. Every participant's original health survey, which recorded smoking status, alcohol intake, physical activity, height, weight, education level, and diabetes status, was linked at the individual level to Finland's national Cancer Registry, which has tracked cancer diagnoses with high accuracy since 1953. The researchers used Poisson regression models to calculate both hazard ratios (HRs, how much a given risk factor raises or lowers someone's chance of developing colorectal cancer relative to a reference group) for each risk factor, and separately, the average annual percentage change (AAPC) in incidence over time within each risk factor group. A sensitivity analysis that shortened the follow-up window to 10 and 15 years after the original survey did not change the study's conclusions.

What This Means for Managing Your Own Risk

If you're trying to figure out what's actually worth changing, this study's clearest, most actionable signal is quitting or never starting smoking for men, and moderating heavy alcohol use for women, both showed real, statistically solid associations with colorectal cancer risk. Maintaining a healthy body weight mattered for both sexes, and managing diabetes was independently associated with lower risk in both men and women too. Being tall is a genuine, replicated risk factor (tallest third of men carried a 41% higher risk, tallest third of women a 24% higher risk, compared to the shortest third), but it isn't something anyone can act on, and the study doesn't identify a mechanism; it's worth knowing about if a doctor is calculating your personal risk profile, not something to worry about changing. If you're someone who skipped screening because you assumed you were "low risk" due to good diet or education level, this study is a reason to reconsider: neither education nor physical inactivity predicted colorectal cancer risk here, which means those factors shouldn't be used to reassure yourself out of standard screening at the recommended age. The CDC lists smoking, heavy alcohol use, excess weight, and inactivity among the modifiable risk factors worth discussing with a doctor.

The Education and Inactivity Result Needs Careful Reading

Two of the study's least expected findings deserve extra scrutiny. First, physical inactivity did not significantly predict colorectal cancer risk in either men or women, despite being widely accepted as a CRC risk factor in prior research; this may partly reflect that physical activity data were entirely unavailable ("missing by protocol") for 13.1% of men and 10.9% of women, because two of the seven pooled cohorts never collected it. Second, education level was not a statistically significant risk factor for developing colorectal cancer in this study, which is notable because Finland has historically shown the opposite pattern in the broader population, with colorectal cancer historically concentrated in higher socioeconomic status groups. That established Finnish pattern doesn't disappear in this data, it shows up differently: low-education men saw colorectal cancer incidence rise faster over time (2.1% per year) than middle-education men (no significant trend), even though education itself didn't predict who got the disease. Alcohol data had a similar gap, missing by protocol for 16.5% of men and 14.1% of women. Several other estimates were only borderline significant, including the middle height tertile in men (HR 1.21, 95% CI 1.01 to 1.45, barely clearing the threshold) and overweight (not obese) women, where the extra risk from carrying excess weight was not statistically significant (HR 1.13, 95% CI 0.97 to 1.32).

What Comes Next

The study's authors point to changes in cigarette composition, shifts in how physical activity was measured across decades, and evolving population-level risk behaviors as possible contributors to the patterns they found, without being able to test any of those explanations directly with this dataset. Because risk factors were measured only once, at the start of each person's participation, and some people were followed for over 40 years afterward, the authors flag that people's actual smoking, drinking, weight, and activity levels likely changed in ways the study couldn't capture, which could bias the results in either direction. Follow-up work that re-measures these risk factors periodically, rather than once, would help clarify how much of the still-unexplained rise in colorectal cancer reflects exposures the study didn't fully capture.

Common Questions

Does this study explain why colorectal cancer rates are rising in younger people? Not directly. This study wasn't designed to isolate early-onset (under-50) colorectal cancer specifically, but it does show that known lifestyle risk factors don't fully account for the overall rising trend in Finland, a pattern many other countries are also seeing.

Is height actually a risk factor for colorectal cancer, or is that a fluke? It's a well-replicated finding across multiple studies, including this one, where taller men and women had meaningfully higher colorectal cancer risk, but researchers still don't know the underlying mechanism, and it isn't something a person can change.

If I have a low physical activity level, does that mean I'm not at higher colorectal cancer risk? Not necessarily. This particular study did not find physical inactivity to be a statistically significant risk factor, but that result may partly reflect missing data, and other well-established organizations still list inactivity among known modifiable colorectal cancer risk factors.

Does this study mean people with more education don't need to worry about colorectal cancer? No. Education level wasn't a significant predictor of who developed colorectal cancer in this dataset, but Finland has historically shown higher CRC rates in higher-education groups in other data, so this single finding shouldn't be read as a green light to skip screening at the recommended age.

References

Emilia Muhonen, Karri Seppä, Heidi Ryynänen, et al. (2026). Incidence Trends of Colorectal Cancer by Social and Behavioral Factors—A Pooled Cohort Study. International Journal of Cancer. https://doi.org/10.1002/ijc.70656