Constipation and Colorectal Cancer: Evidence-Based Assessment
Chronic constipation is not a significant independent risk factor for colorectal cancer, despite earlier conflicting evidence suggesting a possible association. The most rigorous and recent nationwide case-control study from Sweden found no true association after controlling for confounding factors 1.
Key Evidence from High-Quality Studies
The Definitive Swedish Study (2022)
The largest and most methodologically robust investigation examined 41,299 colorectal cancer cases matched with 203,181 controls across Sweden 1. Key findings include:
- Initial crude analysis showed a modest association (OR 1.10,95% CI 1.06-1.14) between chronic constipation and colorectal cancer 1
- However, this association completely disappeared when using sibling comparators to control for residual confounding (OR 1.04,95% CI 0.97-1.13), indicating the initial association was due to shared familial and environmental factors rather than constipation itself 1
- Sensitivity analysis of 126,650 colorectal cancer patients found no association with earlier chronic constipation diagnosed in specialty clinics (OR 0.88,95% CI 0.75-1.04) 1
Conflicting Earlier Evidence
Older studies suggested possible associations, but had significant methodological limitations:
- A 2014 US claims database study reported increased risk (IRR 1.59 for colorectal cancer, IRR 2.60 for benign neoplasms) 2, but this was based on administrative claims data without adequate control for confounding factors
- A 1998 case-control study found frequent constipation associated with increased risk (RR 4.4 for ≥52 episodes/year) 3, but this predated modern epidemiological methods and had smaller sample size
- A 2011 Japanese study reported modest increased risk (OR 1.51-1.60) 4, but was limited by regional population and smaller scale
Clinical Implications and Pitfalls
What Constipation May Actually Indicate
Constipation should not be dismissed entirely, as it may be a symptom rather than a cause of colorectal pathology:
- Rectal prolapse patients have a 4.2-fold increased relative risk of colorectal cancer, and constipation is a common associated symptom 5
- New-onset constipation or change in bowel habits in older adults warrants colonoscopic evaluation to rule out obstructing colorectal cancer 5
- Any colonic stricture in the setting of chronic symptoms should be considered malignant until proven otherwise 6
True Risk Factors to Focus On
Rather than constipation itself, clinicians should focus on established modifiable risk factors for colorectal cancer:
- Smoking is strongly associated with colorectal adenomas with a three to four decade induction period 7
- Physical inactivity consistently increases risk, while moderate regular activity is protective 7
- Obesity and elevated BMI increase colorectal cancer risk 7
- High consumption of red and processed meat is associated with increased polyp risk 7
- Excessive alcohol consumption increases risk, particularly when combined with familial predisposition 7
Surveillance Recommendations
Standard colorectal cancer screening guidelines should be followed regardless of constipation status:
- Average-risk individuals should begin screening according to national guidelines (typically age 45-50) 5
- Patients with inflammatory bowel disease (ulcerative colitis or Crohn's colitis) should begin surveillance at 8 years after disease onset 5, 6
- Those with primary sclerosing cholangitis, extensive colitis, or family history require more intensive surveillance 5, 6
Bottom Line for Clinical Practice
Do not attribute increased colorectal cancer risk to chronic constipation alone. The most recent high-quality evidence refutes this association 1. However, use new-onset constipation or significant change in bowel habits as a clinical indicator to pursue appropriate diagnostic evaluation for underlying colorectal pathology, particularly in patients over age 50 or those with alarm features 5. Focus preventive counseling on established modifiable risk factors including smoking cessation, regular physical activity, weight management, and dietary modification 7.