Colorectal Cancer
Cancer affecting the colon or rectum, often preventable through screening.
TL;DR
Screening and fibre intake have real evidence. Supplements do not prevent colorectal cancer, and calcium and folate data are more complicated than commonly claimed.
Overview
Colorectal cancer develops over years through the adenoma-to-carcinoma sequence, which is precisely why screening works: removing an adenomatous polyp prevents a cancer that would otherwise have developed. Faecal immunochemical testing and colonoscopy both reduce mortality, and uptake matters far more than any dietary refinement. Incidence in adults under 50 has been rising for three decades for reasons that remain unclear, which is why new rectal bleeding or bowel habit change in a younger adult should not be dismissed as haemorrhoids. On supplements, the picture is unflattering. Calcium modestly reduces adenoma recurrence in some trials but showed a possible increase in serrated polyps in others. Folate supplementation appears protective before neoplasia develops and potentially growth-promoting afterwards, a dual effect that argues against routine high-dose use. Aspirin has the strongest chemoprevention evidence and is a medication decision, not a supplement one.
Common Symptoms
- •Change in bowel habit lasting over six weeks
- •Rectal bleeding or blood mixed with stool
- •Iron deficiency anaemia without obvious cause
- •Abdominal pain or bloating
- •Unexplained weight loss
- •A feeling of incomplete emptying
Common Causes
- •Age over 50, though incidence under 50 is rising
- •Family history and Lynch syndrome or FAP
- •Inflammatory bowel disease
- •Obesity and physical inactivity
- •Processed and red meat intake
- •Smoking and alcohol
- •Type 2 diabetes
Root Causes
Progressive accumulation of mutations in APC, KRAS, TP53 and mismatch repair genes converting normal mucosa to adenoma to carcinoma, accelerated by inflammation, obesity, and dietary pattern.
How It's Diagnosed
Diagnostic Markers
- Faecal immunochemical test (FIT)
- Colonoscopy with polypectomy
- Full blood count and ferritin
- CEA for monitoring after diagnosis, not for screening
- CT for staging
When to See a Doctor
Arrange prompt review for rectal bleeding, a bowel habit change lasting over six weeks, unexplained iron deficiency anaemia, or unexplained weight loss — at any age.
Supplements Studied For This
Diet & Lifestyle
Suggested Pattern
High-fibre, plant-forward eating with limited processed meat. Fibre from food has better evidence than any fibre supplement.
Eat more
- Whole grains, legumes, vegetables and fruit to reach 30g fibre daily
- Resistant starch sources such as cooled potato, oats and pulses
- Fish and poultry in place of processed meat
- Dairy in normal dietary amounts
Avoid
- Processed meats: bacon, ham, salami, sausages
- Large quantities of red meat
- Alcohol
- High-dose folic acid supplements without a clinical indication
Supporting Research
Vitamin D supplementation and cancer incidence and mortality: VITAL randomized controlled trial
Efficacy of adjuvant immunochemotherapy with polysaccharide K for patients with curatively resected colorectal cancer: a meta-analysis of centrally randomized controlled clinical trials
Effect of supplementation with marine omega-3 fatty acid on risk of colorectal adenomas and serrated polyps in the US general population
Can polysaccharide K improve therapeutic efficacy and safety in gastrointestinal cancer? A systematic review and network meta-analysis
Prolonged effect of calcium supplementation on risk of colorectal adenomas in a randomized trial
Frequently Asked Questions
Who It Affects
The third most common cancer worldwide, with a lifetime risk of roughly 1 in 20 in high-income countries.
Risk rises after 50, but incidence in under-50s has increased substantially and is now a recognised concern.
Quick Facts
- •Removing an adenoma prevents the cancer it would have become
- •Processed meat is classified as a group 1 carcinogen for colorectal cancer
- •Iron deficiency anaemia in a man or post-menopausal woman warrants colonoscopy
- •Under-50 incidence has risen steadily since the 1990s
Lifestyle Tips
- •Complete screening when invited — this is the highest-impact action available
- •Aim for 30g of fibre daily from whole foods
- •Limit processed meat and keep red meat modest
- •Maintain a healthy weight and stay physically active
- •Stop smoking and reduce alcohol
- •Do not use high-dose folate supplements as chemoprevention
My Notes
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This information is for educational purposes only. Always consult a healthcare professional before starting any supplement regimen.