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Colon Cancer

Colorectal cancer is the third most common cancer worldwide, yet its incidence can be reduced by a healthy lifestyle, and screening finds polyps before they become cancer15. The gut microbiome is an active area of colorectal cancer research, though no trial yet shows that changing it changes outcomes.

Cancer Evidence-Based

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⚠️ Treatment safety: please read first. The nutrition and supplement approaches on this page are meant to work alongside cancer treatment, never to replace or delay it. Never stop, delay or change your treatment without your oncology team's guidance. Doing so can be dangerous. Several supplements interact with chemotherapy and other cancer treatments, so talk to your oncology team or pharmacist before starting anything on this page.
Definition

What Is Colorectal Cancer?

Colorectal cancer (CRC) is a malignancy arising from the epithelial lining of the colon (large intestine) or rectum. It usually develops slowly, over many years16, through a well-characterized progression from normal epithelium to adenomatous polyp to invasive carcinoma, providing a wide window for detection and prevention.

Most colorectal cancers are adenocarcinomas16, originating from the glandular cells lining the colon wall. Rarer types include neuroendocrine tumors, gastrointestinal stromal tumors, lymphomas and squamous cell carcinomas.

Emerging evidence links the gut microbiome to colorectal cancer risk. Specific bacteria, notably Fusobacterium nucleatum6, Peptostreptococcus anaerobius and enterotoxigenic Bacteroides fragilis, are found enriched in colorectal tumors and, in laboratory studies, promote carcinogenesis through inflammation, barrier disruption and oncogenic signaling6.

A front view of the abdomen with the large intestine around the coiled small intestine, and a round tumor on the wall of the colon on the body's left side

5-⁠Year Relative Survival by How Far It Has Spread

Localized

91%

Still confined to where it started (US, 2016 to 2022)17

Regional

75%

Spread to nearby lymph nodes (US, 2016 to 2022)17

Distant

17%

Spread to distant organs (US, 2016 to 2022)17

Early detection is the most powerful intervention: in US data for 2016 to 2022, which group cancers by how far they have spread rather than by stage number, 5-⁠year relative survival is 91% when localized, 75% after spread to nearby lymph nodes and 17% after spread to distant organs17. Screening saves lives.

By the Numbers

Colorectal Cancer by the Numbers

1.9M
new colorectal cancer cases worldwide in 2022, the third most common cancer15
2nd
leading cause of cancer death worldwide15
45
age at which US guidelines start screening for people at average risk; in England, home test kits go to everyone aged 50 to 74 22
91%
5-⁠year relative survival in the US when found while still localized, against 17% once it has spread to distant organs (2016 to 2022 data)17
26%
fewer colorectal cancer deaths in randomized trials of one or two flexible sigmoidoscopy screenings, compared with no screening21
18%
higher colorectal cancer risk for every 1.8 oz (50 g) of processed meat eaten daily; its IARC Group 1 label reflects how certain that link is, not how large32
Signs & Symptoms

Symptoms of Colorectal Cancer

See a doctor promptly for any of these warning signs; do not wait for them to pass. Heavy bleeding, black tarry stools or signs of a blocked bowel need emergency care (see When to Seek Care). Who is at higher risk, which guides when and how often to screen, is covered in the next section.

SymptomWhat happens
Warning Signs (See a Doctor Promptly)
Rectal Bleeding or Blood in StoolBright red blood on toilet paper (may indicate low rectal or anal source) or dark, maroon blood mixed in stool (higher colonic source). Never assume rectal bleeding is just hemorrhoids without evaluation: blood in the stool is one of the main symptoms of colorectal cancer18.
Persistent Bowel Habit ChangesPersistent diarrhea, constipation or "pencil-thin" stools lasting more than 4 weeks; a narrowing stool caliber is particularly concerning as it suggests a luminal-narrowing tumor. Any unexplained, persistent change in bowel habits, at any age, needs a doctor's assessment, which may include colonoscopy.
Unintentional Weight LossLosing weight without trying, with no change in diet or exercise, is one of the listed symptoms of colorectal cancer and needs a doctor's assessment18. Weight loss can be driven by tumor-produced cytokines (cachexia factors) that shift metabolism toward catabolism and suppress appetite.
Persistent Abdominal Pain, Cramping & BloatingPersistent or worsening lower abdominal cramping, gas, fullness or pain that doesn't respond to dietary changes or IBS treatment. Pain may indicate partial obstruction from a large tumor. Always have new, unexplained abdominal symptoms checked, whatever your age.
Causes

Causes of Colorectal Cancer

Most colorectal cancers start as polyps that change into cancer over many years16; some risks can be changed and some cannot, and screening is the step that finds polyps before they become cancer3.

CauseHow It Contributes to Colorectal CancerWhat Helps
Age, and polyps that are not removedMost colorectal cancers begin as a growth on the lining of the bowel, and some polyps change into cancer over years16; risk rises markedly after 50, though rates are rising in younger adults in some countries15Screening from 45 in the US, or the NHS home test every 2 years from 50 to 74 in England, as the diagnosis section describes22
Processed and red meatThere is convincing evidence that processed meat, such as hot dogs, ham and sausages, causes colorectal cancer, and each 1.8 oz (50 g) eaten daily raises risk by about 18%; its IARC Group 1 category reflects how certain the link is, not how large the risk is32Little, if any, processed meat and no more than moderate red meat26, as the diet section sets out
Alcohol, excess weight, inactivity and smokingWHO lists physical inactivity, overweight and obesity, tobacco use and alcohol among the lifestyle factors that increase risk15Less or no alcohol, a healthy weight, not smoking and regular activity; after treatment, a 3-⁠year structured exercise program lengthened disease-free survival in a randomized trial25
Low fiber and whole-grain intakeDiets low in fruit and vegetables are among the listed risks15; in cohort studies each 10 g a day of cereal fiber is associated with about 9% lower risk1The high-fiber, whole-grain pattern in the diet section; these are associations from cohort studies, not a proven effect
Gut bacteriaA bacterium, Fusobacterium nucleatum, is found in higher amounts in some colorectal tumors, and laboratory studies suggest it may help them grow6No probiotic or other change to the gut bacteria has been shown in a randomized trial to prevent colorectal cancer6
Family history and inherited syndromesA parent, sibling or child with colorectal cancer raises risk, more so if diagnosed before 50; Lynch syndrome, from a change in one of the mismatch repair genes (MLH1, MSH2, MSH6 or PMS2), is the most common inherited syndrome, with the highest lifetime risk for MLH1 and MSH2; in classic FAP at least 90% develop colorectal cancer by 50 without preventive surgery19Earlier and more frequent colonoscopy and genetic counseling; no diet or supplement on this page changes inherited risk
Inflammatory bowel diseaseLong-standing ulcerative colitis or Crohn's colitis raises risk; in a meta-analysis of ulcerative colitis, cumulative risk was 2% by 10 years, 8% by 20 and 18% by 30 20Surveillance colonoscopy on the schedule your gastroenterologist sets
Diagnosis

How Colorectal Cancer Is Diagnosed

Colonoscopy can both detect AND prevent colorectal cancer: polyps removed during colonoscopy never become cancer. Regular screening prevents colorectal cancer, not only detects it3.

TestWhat it shows
Colonoscopy & Structural Tests
Colonoscopy (Gold Standard)Direct visualization of the entire colon with immediate polypectomy. Detected 89% of adenomas 6 mm or larger in pooled studies21. Recommended every 10 years for average-risk individuals, whom US guidelines advise screening from 45 through 75 22; sooner after polyp removal, from 3 to 10 years depending on what was found23; every 1 to 2 years for some high-risk groups (IBD, Lynch syndrome); after colorectal cancer, 1 year after surgery and then about every 5 years43. Removing polyps prevents them from becoming cancer3.
CT Colonography (Virtual Colonoscopy)3D CT imaging of the colon, no sedation required, but also no polypectomy. Detected 86% of adenomas 6 mm or larger in pooled studies21. Recommended every 5 years. If polyps are found, conventional colonoscopy is then required for removal. Good alternative for patients unwilling or unable to tolerate colonoscopy preparation or sedation.
Flexible SigmoidoscopyViews only the left colon and rectum; in randomized trials, one or two screenings lowered colorectal cancer deaths by about a quarter21. Recommended every 5 years alone or every 10 years combined with annual FIT test. Less preparation required than colonoscopy. A positive sigmoidoscopy requires follow-up colonoscopy.
Non-Invasive Tests
Multitarget Stool DNA TestTests stool for abnormal DNA from cancer cells AND occult blood. Detected 92% of cancers and 42% of advanced precancerous lesions in its main trial21. Recommended every 3 years. Higher false-positive rate than FIT; a positive stool DNA test requires confirmatory colonoscopy. Does not allow polyp removal.
FIT Test (Fecal Immunochemical Test)Detects occult (hidden) blood in stool using antibodies, no dietary restrictions required. FIT detected 74 to 79% of cancers in pooled studies21. Recommended annually. A positive FIT requires colonoscopy. The most accessible screening test; in England, the NHS mails a kit every 2 years to everyone aged 50 to 74 22.
CEA Blood Test (Monitoring)Carcinoembryonic antigen, a tumor marker used for post-treatment surveillance, not screening (too low sensitivity for early detection). A raised or rising CEA after treatment can be a sign of residual or recurrent disease and is checked with further tests. Baseline CEA before surgery is useful for tracking treatment response.
Treatment Comparison

Conventional and Holistic Treatment for Colorectal Cancer

⚠️ Colorectal cancer requires conventional oncological treatment. The holistic approach here refers to nutritional and lifestyle strategies that support treatment outcomes and prevention, reduce side effects and may lower recurrence. It is not a replacement for surgery, chemotherapy or radiation.

🌿 HOLISTIC
💊 CONVENTIONAL
🌿

Holistic / Functional Approach

Diet, gut health and supportive nutrition alongside treatment; diet patterns are linked with lower recurrence in observational studies

Primary Focus
Maintain nutrition and weight, manage treatment side effects, and follow the diet and activity patterns linked with lower recurrence
Evidence Base
Observational studies link higher fiber and whole-grain intake2 and physical activity12 with lower recurrence and better survival; vitamin D findings are observational only4
Recurrence Evidence
Higher whole-grain and cereal-fiber intake after diagnosis was associated with lower recurrence and mortality in one prospective cohort2.
Timing
Pre-treatment: optimize nutritional status; During: manage side effects; Post: reduce recurrence risk

Full Holistic Approach Includes

  • High-fiber diet (30 to 35 g/day from whole foods): butyrate produced from fiber fermentation is the primary fuel of colonocytes; its effects on cancer cells come from laboratory studies6
  • Cruciferous vegetables (broccoli, cauliflower, Brussels sprouts) daily: sulforaphane and indole-⁠3-⁠carbinol are among the most extensively studied chemopreventive compounds; sulforaphane inhibits CRC cell proliferation and induces apoptosis in laboratory studies
  • Studied but not recommended: curcumin inhibits NF-κB, COX-⁠2 and Wnt/β-catenin pathways in the laboratory. Early-phase human work reached measurable tissue concentrations, but the randomized trial in familial adenomatous polyposis was negative5
  • Vitamin D repletion (target set with your clinician): low vitamin D is associated with higher CRC risk in observational studies, but randomized supplementation trials have not shown lower incidence4
  • Studied but not recommended: omega-⁠3 fish oil for preventing polyps, since in a randomized trial EPA did not reduce colorectal adenomas24
  • Probiotics (specifically Lactobacillus and Bifidobacterium species) have been studied for effects on Fusobacterium nucleatum and colonic immune responses, without trial evidence of fewer cancers
  • Exercise (150+ minutes moderate activity/week), associated with lower recurrence and mortality in stage III patients in an observational study12; in a randomized trial, a 3-⁠year structured exercise program started after chemotherapy lengthened disease-free survival25
  • Green tea (3 to 5 cups/day; as an extract, 300 mg EGCG a day, and more only with your clinician, as the supplement table explains): epigallocatechin gallate inhibits CRC proliferation pathways in the laboratory. The one large randomized trial (MIRACLE, 1,001 patients over 3 years) did not reach significance: 51.1% adenoma recurrence on EGCG against 55.7% on placebo11
  • Eat little, if any, processed meat, as cancer prevention advice recommends26; after stage III treatment, one cohort found no link with recurrence2
⚠️ During chemotherapy: Some supplements (high-dose antioxidants, certain herbs) may interfere with chemotherapy. Always disclose all supplements to your oncologist.
Supplement Protocol

Evidence-Based Supplements for Colorectal Cancer

The following supplements have been studied for colorectal cancer prevention, treatment side effects or recurrence; where randomized trials found no benefit, the row says so. All should be discussed with your oncologist before use during active treatment.

SupplementWhat it is forTypical rangeTimingNotes & cautions
Vitamin D3 (with K2)The most studied supplement for CRC prevention, with observational rather than trial support4. Meta-analyses report roughly 35 to 40% lower colorectal cancer risk comparing the highest with the lowest 25-⁠OH-D categories, pooled RR about 0.62. An observational association across categories, not a demonstrated effect of reaching a particular level4. In the phase 2 SUNSHINE trial of 139 patients with advanced or metastatic CRC, adding high-dose vitamin D3 to chemotherapy did not significantly lengthen median progression-free survival, though a supportive analysis favored it48.Set the dose with your clinician; most adults need no blood test first. D3 with K2 (MK-⁠7, 200 mcg)With the largest fat-containing mealSome people pair D3 with K2; an agreed dose, not K2, is what prevents high calcium. If you take a blood thinner that works against vitamin K, clear any K2 with whoever manages it first34.
CurcuminIn laboratory studies it inhibits NF-κB, COX-⁠2 and Wnt/β-catenin signaling in CRC cells. An early-phase clinical trial found measurable curcumin concentrations in colorectal tissue at 3.6 g/day. An early uncontrolled report in 5 patients used curcumin plus quercetin and described fewer, smaller polyps, but a randomized double-blind trial in 44 patients on 3,000 mg/day for 12 months found no difference in polyp number or size against placebo5.Not recommended for preventing polyps (the trial used 3,000 mg a day)Not applicableLiver damage has been reported with the more absorbable forms: stop and see a clinician if you notice fatigue, nausea, poor appetite, dark urine or yellowing skin35. Piperine (black pepper extract) can affect drug metabolism; avoid with chemotherapy.
Omega-⁠3 Fish Oil (EPA+DHA)In the randomized seAFOod trial of 709 people at high risk, 2 g/day of EPA for 12 months did not reduce colorectal adenomas24. In the VITAL trial, omega-⁠3 supplementation did not lower overall cancer incidence49.Not recommended for preventing polyps (the trial used 2 g of EPA a day)Not applicableDiscuss with oncologist if on anticoagulants. In heart trials, fish oil supplements raised the risk of atrial fibrillation, an irregular heartbeat, more so above 1 g a day47, so check any fish oil supplement with your clinician first.
Probiotics (Multi-Strain)Studied for effects on the altered microbiome seen in many CRC patients. Effects on F. nucleatum and butyrate come from laboratory and small human studies6. In a randomized trial of 150 patients on fluoropyrimidine-based chemotherapy for colorectal cancer, Lactobacillus rhamnosus GG cut severe diarrhea from 37% to 22%36.50 to 200 billion CFU/day (multi-strain)Away from chemotherapy administration timing (ask oncologist)Some chemotherapy protocols require a 48-⁠hour probiotic-free window around infusion day. People on chemotherapy can be immunocompromised. Use caution with a weakened immune system or a central line, as bloodstream infections from probiotics have been reported; agree on it with your team.
Sulforaphane (from Broccoli Sprout Extract)In laboratory studies it induces Nrf2-⁠controlled enzymes that inactivate carcinogens. Myrosinase (from broccoli sprouts or from mustard seed powder added to cooked broccoli, since cooking destroys it) converts glucoraphanin to active sulforaphane, essential for efficacy. A 2023 review of randomized trials found none in colorectal cancer, and inconsistent results in prostate, breast and pancreatic cancer and melanoma37.100 to 400 mg/day of a stabilized sulforaphane product or about 1/3 to 2/3 oz (10 to 20 g) of broccoli sprouts daily; agree on the product and amount with your oncology teamWith mealsNot shown to help colorectal cancer, as no trial has tested it. Broccoli sprouts contain 10 to 100 times more glucoraphanin than mature plants38.
Green Tea Extract (EGCG)In laboratory studies epigallocatechin gallate (EGCG) inhibits several growth signals in CRC cells. A small pilot trial in Japan, in 136 people whose adenomas had been removed, reported fewer new adenomas after 12 months with green tea extract (15% against 31%)14, but the much larger MIRACLE trial of 1,001 patients did not reach statistical significance11.300 to 600 mg EGCG/day (standardized extract); the large trial used 300 mg a day and did not reach significance, so check any dose above 300 mg with your clinicianWith meals, to reduce nauseaHigh doses of EGCG (>800 mg/day) can cause liver enzyme elevation9. Start at 300 mg and increase gradually. Avoid taking within 2 hours of iron supplements; EGCG chelates iron. Discuss with oncologist before use during active treatment.
Glutamine (L-Glutamine)Glutamine is the primary fuel of rapidly dividing intestinal epithelial cells and immune cells. In a randomized trial of 70 patients on fluoropyrimidine chemotherapy for colorectal cancer, 18 g/day lessened gut absorption and permeability changes and may have reduced diarrhea39.10 to 20 g/day during treatmentFasted, morning and before bed; split dosesSupportive-care guidelines could not recommend it for gut mucositis because the evidence is inconsistent39. Contraindicated in hepatic encephalopathy and glutamine-responsive tumor types (discuss with oncologist).
FolateFolate deficiency disrupts DNA methylation and nucleotide synthesis, increasing mutation rate in rapidly dividing colonocytes. In a randomized trial of 1,021 people with previous adenomas, 1 mg/day folic acid did not reduce new adenomas and was linked to more advanced and multiple ones40. Methylfolate (5-⁠MTHF) is one form of folate; common MTHFR variants do not usually prevent the use of folic acid. Important: folic acid supplementation of 1 mg/day or more in patients with existing precancerous polyps or undergoing treatment should be discussed with an oncologist.Not recommended for preventing polyps (the trial used 1 mg of folic acid a day)Not applicableFolate from food (dark leafy greens, legumes) is safe and recommended universally. High-dose supplementation during active cancer treatment needs your oncologist's agreement: 5-⁠FU chemotherapy is given with leucovorin, a form of folate, so folate dose and timing matter. If a blood test shows a low level, your oncologist sets the dose.
What to Expect

What to Expect Over Time

What happens depends on the stage and where the cancer is; your specialist team plans it with you41.

Treatment and supportive care, together
First Weeks

Surgery removes the cancer with part of the bowel, sometimes with a temporary or permanent stoma41. Tell the team about every supplement first: antioxidants and herbs might interfere with chemotherapy42.

Months 1 to 3

After surgery for stage III, chemotherapy usually follows to lower the chance of recurrence, for 3 or 6 months depending on risk27; rectal cancer may also need radiation therapy41. Diet supports weight and eases side effects; it replaces none of this.

Months 3 to 12

Follow-up usually means an examination and CEA blood test every 3 to 6 months, a yearly CT scan for 3 years, and a colonoscopy 1 year after surgery43.

Long Term

Colonoscopy then repeats about every 5 years43, and staying active matters: a 3-⁠year exercise program after chemotherapy lengthened disease-free survival in a randomized trial25. If the cancer cannot be removed, treatment aims to slow it and ease symptoms, with palliative care41.

When to Seek Care

Call 911 or go to the emergency department for heavy bleeding, black tarry stools or dizziness from bleeding44, or for sudden severe abdominal pain with vomiting or no stool or gas passing, a possible blocked bowel45. On chemotherapy, a fever or chills needs your care team or emergency care at once, because it can be an infection46. See a doctor promptly for a lasting change in bowel habit, blood in your stool or weight loss without trying18.

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Next Steps

Screening and Diet Work Together

A healthy, diverse gut microbiome, a high-fiber whole-food diet, less processed meat and alcohol, and regular activity are associated with lower colorectal cancer risk. Get screened when you become eligible, and if you have a personal or family history, ask about earlier screening22.

Explore IBS & IBD → Explore Hemorrhoids →

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed October 20, 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.10 Read this before anything else on the page. Nothing here treats colorectal cancer. Diet and supplements are adjunctive: they support nutritional status, help manage treatment side effects, and are associated with lower recurrence risk in observational studies. They are not an alternative to surgery, chemotherapy, radiation therapy or immunotherapy, and no dietary change should delay or replace treatment decided with your oncology team. Tell your oncologist about every supplement you take, because several in the list below interact with chemotherapy. Screening is the step on this page with the strongest evidence.

  1. World Cancer Research Fund / American Institute for Cancer Research, Continuous Update Project, colorectal cancer. wcrf.org. Source for the dose-response figures used on this page: roughly 10% lower risk per 10 g/day of dietary fiber, close to the 0.91 relative risk per 10 g/day of cereal fiber found in a dose-response meta-analysis of prospective studies, PubMed 31495339, about 7% higher risk per alcoholic drink per day, and the processed-meat and red-meat associations. These are population-level associations from prospective cohorts, not individual predictions. ↩ ↩
  2. Meyerhardt JA, et al. Association of dietary patterns with cancer recurrence and survival in patients with stage III colon cancer. JAMA / CALGB 89803 cohort, 1,009 patients. PubMed 17699009. Higher whole-grain intake was associated with about 35% lower recurrence and mortality (highest versus lowest quartile), and each 5 g/day increase in cereal fiber after diagnosis with about 33% lower colorectal-cancer-specific mortality. Importantly, a later analysis of the same cohort found post-diagnosis unprocessed red meat and processed meat were NOT associated with recurrence or death, PubMed 35191970. Observational: patients who eat more whole grains differ in other ways too. ↩
  3. On screening: American Cancer Society guideline lowering the start of average-risk screening to age 45, and the evidence that colonoscopic polypectomy prevents cancer rather than only detecting it. cancer.org. ↩
  4. On vitamin D: 25-⁠Hydroxyvitamin D Status and Risk for Colorectal Cancer, systematic review and meta-analysis, PMC5334681, pooled RR 0.62 comparing highest with lowest 25-⁠OH-D category, and the dose-response meta-analysis in J Steroid Biochem Mol Biol. These are observational associations. Randomized vitamin D supplementation trials have not shown a reduction in colorectal cancer incidence, which is the main reason this is framed as an association rather than an effect. ↩
  5. On curcumin in familial adenomatous polyposis, read both trials together. Cruz-Correa M, et al. Combination treatment with curcumin and quercetin of adenomas in FAP. Clin Gastroenterol Hepatol. 2006, cghjournal.org: five patients, uncontrolled, curcumin plus quercetin, mean 60.4% decrease in polyp number and 50.9% in size. Then Cruz-Correa M, et al. Efficacy and safety of curcumin in treatment of intestinal adenomas in patients with FAP. Gastroenterology. 2018, PubMed 29802852: 44 patients, randomized, double-blind, 3,000 mg/day for 12 months, no significant difference in polyp number or size versus placebo. The randomized trial is the stronger evidence. ↩
  6. On the microbiome and Fusobacterium nucleatum in colorectal cancer, and on butyrate-producing genera as the mechanism proposed for fiber's association with lower risk. Mechanistic and observational; no randomized trial shows that changing the microbiome changes colorectal cancer outcomes. ↩
  7. On processed meat: IARC Monographs Volume 114 classified processed meat as Group 1 (carcinogenic to humans) and red meat as Group 2A. iarc.who.int. Group 1 describes the strength of evidence that something can cause cancer, not the size of the risk, which is why the comparison with tobacco is about certainty rather than magnitude. ↩
  8. On chemotherapy after surgery: in the MOSAIC randomized trial of 2,246 people with stage II or III colon cancer, adding a platinum drug to fluoropyrimidine chemotherapy (the FOLFOX regimen) lowered the risk of recurrence, with 21.1% against 26.1% having a cancer-related event at a median of 37.9 months (hazard ratio for recurrence 0.77), PubMed 15175436; at final analysis the 5-⁠year disease-free survival hazard ratio was 0.80, PubMed 19451431. Treatment selection is individual and belongs with an oncology team. ↩
  9. On EGCG: high intakes have been associated with liver enzyme elevation, and EGCG can reduce iron absorption. A United States Pharmacopeia review of green tea extract found the injury pattern is linked to large single doses taken on an empty stomach rather than to tea drunk as a beverage, PubMed 32140423. See NCCIH, ref. 10. ↩
  10. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic. ↩
  11. Seufferlein T, et al. MIRACLE: green tea extract versus placebo for the prevention of colorectal adenomas, a randomized controlled trial. Ann Oncol. annalsofoncology.org. 1,001 patients randomized to decaffeinated EGCG 150 mg twice daily or placebo for three years after polypectomy. Adenoma recurrence was 51.1% on EGCG against 55.7% on placebo, adjusted RR 0.904, one-sided adjusted p = 0.077. The trial did not reach statistical significance. No safety concerns emerged. ↩
  12. On physical activity after colon cancer treatment: a 2006 prospective observational study of 832 patients with stage III colon cancer, enrolled in an adjuvant chemotherapy trial, found better disease-free survival in those reporting 18 or more MET-hours of activity a week than in those reporting fewer than 3, with similar findings for recurrence-free and overall survival. Being observational, it shows an association rather than a proven effect, PubMed 16822843. ↩
  13. On first-line immunotherapy for MSI-High colorectal cancer: a 2020 phase 3 trial randomized 307 previously untreated patients with metastatic MSI-High, mismatch repair-deficient colorectal cancer to pembrolizumab or chemotherapy. Progression-free survival was longer with pembrolizumab, median 16.5 against 8.2 months, overall response was 43.8% against 33.1%, and grade 3 or higher treatment-related adverse events were fewer, 22% against 66%, PubMed 33264544. ↩
  14. On the earlier green tea extract trial: a randomized pilot study in 136 Japanese patients whose colorectal adenomas had been removed found new adenomas at 12 months in 15% (9 of 60) on green tea extract against 31% (20 of 65) of controls, PubMed 18990744. ↩
  15. On how common colorectal cancer is and what raises risk: the World Health Organization reports an estimated 1.9 million new cases and more than 900,000 deaths worldwide in 2022, making it the third most common cancer and the second leading cause of cancer death. Risk rises markedly after 50, though several countries report rising rates in younger adults, and the lifestyle risk factors it lists are diets high in processed and red meat and low in fruit and vegetables, physical inactivity, overweight and obesity, tobacco and alcohol. It states that incidence can be significantly reduced by a healthy lifestyle and timely diagnosis, WHO, colorectal cancer. ↩
  16. On how colorectal cancer starts: the American Cancer Society explains that most colorectal cancers start as a growth called a polyp on the inner lining of the colon or rectum, that some types of polyps can change into cancer, usually over many years, and that most colorectal cancers are adenocarcinomas, American Cancer Society, what is colorectal cancer. ↩
  17. On current US survival: in National Cancer Institute registry data for 2016 to 2022, 5-⁠year relative survival for colorectal cancer was 91.3% when it was found still confined to where it started, 75.2% once it had reached nearby lymph nodes and 16.9% once it had spread to distant organs; 65.4% overall. Relative survival compares people with the cancer with the general population and is not an individual prognosis, NCI SEER, colorectal cancer. ↩
  18. On symptoms: NHS guidance lists changes in bowel habit that are not usual for you, needing to go more or less often, blood in the stool, which may look red or black, rectal bleeding, abdominal pain, a lump or bloating, losing weight without trying, and tiredness or breathlessness from anemia, and advises seeing a primary care doctor with any of them, NHS, symptoms of colorectal cancer. ↩
  19. On inherited risk: the American Cancer Society states that a parent, sibling or child with colorectal cancer raises risk, more so if they were diagnosed before 50, and that Lynch syndrome is the most common hereditary colorectal cancer syndrome; US genetics guidance adds that lifetime cancer risk in Lynch syndrome is higher with MLH1 or MSH2 variants than with MSH6 or PMS2, and that at least 90% of people with classic familial adenomatous polyposis develop colorectal cancer by 50 without a preventive colectomy, American Cancer Society, risk factors; MedlinePlus Genetics, FAP; MedlinePlus Genetics, Lynch syndrome. ↩
  20. On ulcerative colitis: a meta-analysis of 116 studies estimated the cumulative probability of colorectal cancer in ulcerative colitis at 2% by 10 years of disease, 8% by 20 years and 18% by 30 years. These are older pooled estimates, PubMed 11247898. ↩
  21. On screening tests: the 2021 evidence review for the US Preventive Services Task Force found that one or two flexible sigmoidoscopy screenings lowered colorectal cancer deaths against no screening in 4 randomized trials of 458,002 people (incidence rate ratio 0.74), that pooled sensitivity for adenomas 6 mm or larger was 89% for colonoscopy and 86% for CT colonography with bowel preparation, and that pooled sensitivity for cancer was 74% for FIT and 93% for stool DNA with FIT, PubMed 34003220. An earlier meta-analysis put FIT sensitivity for cancer at 79%, PubMed 24658694, and in the main stool DNA trial of 9,989 people the test detected 92.3% of cancers and 42.4% of advanced precancerous lesions, against 73.8% and 23.8% for FIT, with more false positives, PubMed 24645800. ↩
  22. On who is screened and when: the US Preventive Services Task Force recommends screening all adults aged 50 to 75 and adults aged 45 to 49, and selective screening from 76 to 85 depending on health and past screening, PubMed 34003218; the American Cancer Society recommends starting at 45 for people at average risk and continuing through 75 for those in good health, American Cancer Society, screening guideline. In England the NHS offers a home FIT kit every 2 years to people aged 50 to 74, with testing on request from 75, NHS, colorectal cancer screening. ↩
  23. On the next colonoscopy after polyps are removed: the 2020 US Multi-Society Task Force update recommends 7 to 10 years after 1 or 2 small adenomas under 10 mm, and 3 years after any adenoma of 10 mm or more, advanced adenoma or serrated polyp of 10 mm or more, PubMed 32044092. ↩
  24. On fish oil and polyps: in the seAFOod randomized trial of 709 people at high risk found through the English bowel screening program, 2 g a day of EPA for 12 months did not lower the proportion with at least one adenoma (63% against 61% on placebo), and gastrointestinal side effects were more common on EPA, PubMed 30466866. ↩
  25. On exercise after treatment: in the CHALLENGE randomized trial of 889 people who had finished chemotherapy for colon cancer, a 3-⁠year structured exercise program lengthened disease-free survival compared with health-education materials alone, with findings consistent with longer overall survival; musculoskeletal side effects were more common with exercise, PubMed 40450658. ↩
  26. On how much meat: the World Cancer Research Fund recommends eating no more than moderate amounts of red meat and little, if any, processed meat, and grades the evidence that processed meat causes colorectal cancer as convincing, World Cancer Research Fund, red and processed meat. ↩
  27. On chemotherapy after surgery: in the MOSAIC trial of 2,246 people with stage II or III colon cancer, adding a platinum drug to fluoropyrimidine chemotherapy (the FOLFOX regimen) lowered the risk of death in stage III (6-⁠year overall survival 72.9% against 68.7%, hazard ratio 0.80), PubMed 19451431; severe (grade 3) sensory neuropathy affected 12.4% during treatment and 1.1% a year later, PubMed 15175436. A pooled analysis of 6 trials in 12,834 people found 3 months of CAPOX as effective as 6, and 3 months enough for lower-risk tumors, while 6 months did better for the highest-risk ones, PubMed 29590544. ↩
  28. On preventing nerve damage from chemotherapy: the 2020 American Society of Clinical Oncology guideline found that no agent is recommended to prevent chemotherapy-induced peripheral neuropathy, discouraged acetyl-L-carnitine for it, and advised adjusting the chemotherapy when neuropathy becomes intolerable, PubMed 32663120. ↩
  29. On cruciferous vegetables: a meta-analysis of 24 case-control and 11 prospective studies found high intake associated with 18% lower colorectal cancer risk (relative risk 0.82), with the prospective studies alone of borderline significance. Observational, PubMed 23211939. ↩
  30. On garlic and onions: a meta-analysis of prospective studies found no association between allium vegetable intake and colorectal cancer risk (relative risk 1.06), and garlic supplement use was associated with slightly higher risk (1.18), a finding the authors said needs confirming, PubMed 24681077. ↩
  31. On meat cooked at high temperatures: the National Cancer Institute explains that heterocyclic amines and polycyclic aromatic hydrocarbons form when meat is cooked at high temperatures, are mutagenic in laboratory experiments and caused tumors in rodents fed high doses, but that population studies have not established a definitive link with cancer in humans; avoiding direct flame, turning meat often and removing charred portions reduce exposure, NCI, chemicals in meat cooked at high temperatures. ↩
  32. On what Group 1 means: the World Health Organization explains that IARC classifications describe the strength of the evidence that something causes cancer, not the level of risk, so processed meat sharing Group 1 with tobacco smoking does not make them equally dangerous; it estimates that each 50 g of processed meat eaten daily raises colorectal cancer risk by about 18%, WHO, red and processed meat. ↩
  33. On ultra-processed food: in three large US cohorts followed for 24 to 28 years, men with the highest intake had 29% higher colorectal cancer risk than those with the lowest (hazard ratio 1.29), while no association was found for overall intake in women. Observational, PubMed 38752573. ↩
  34. On vitamin K and blood thinners: US patient guidance for the most widely used vitamin K antagonist anticoagulant explains that vitamin K affects how it works and advises keeping vitamin K intake consistent, which is why a K2 supplement should be cleared with whoever manages the blood thinner, MedlinePlus. ↩
  35. On curcumin safety: the NIH National Center for Complementary and Integrative Health warns that highly bioavailable curcumin formulations may harm the liver, that liver damage has been reported in some people taking them, and that anyone with fatigue, nausea, poor appetite, dark urine or jaundice should stop and talk with a health care provider, NCCIH, turmeric. ↩
  36. On probiotics during chemotherapy: in a randomized trial of 150 people receiving fluoropyrimidine-based chemotherapy after surgery for colorectal cancer, Lactobacillus rhamnosus GG reduced grade 3 or 4 diarrhea from 37% to 22%, with less abdominal discomfort and fewer dose reductions, and no probiotic-related toxicity was seen, PubMed 17895895. ↩
  37. On sulforaphane trials: a 2023 systematic review of randomized trials in people with cancer found eight, in prostate, breast and pancreatic cancer and melanoma, none in colorectal cancer; effects on biomarkers and outcomes were inconsistent and the trials too varied to pool, PubMed 38074675. ↩
  38. On broccoli sprouts: 3-⁠day-old sprouts of certain broccoli and cauliflower cultivars contained 10 to 100 times more glucoraphanin than the mature plants, PubMed 9294217. ↩
  39. On glutamine: in a randomized trial of 70 people starting fluoropyrimidine chemotherapy for colorectal cancer, 18 g a day of glutamine lessened changes in gut absorption and permeability, and may have reduced diarrhea (the difference was not significant), PubMed 11115819. The 2019 supportive-care (MASCC/ISOO) review of agents for gastrointestinal mucositis could not make a guideline for glutamine because the evidence was inadequate or conflicting, PubMed 31286233. ↩
  40. On folic acid and polyps: in a randomized trial of 1,021 people with recent colorectal adenomas, 1 mg a day of folic acid did not reduce new adenomas, and it was associated with higher risk of advanced lesions at the second follow-up, of 3 or more adenomas and of cancers outside the bowel, PubMed 17551129. ↩
  41. On treatment: NHS guidance explains that treatment depends on the size and place of the cancer, whether it has spread, its genetic changes and your health, may combine surgery, chemotherapy, radiation therapy and targeted medicines, and is planned with a specialist team; surgery may need a temporary or permanent stoma, radiation therapy is used mainly for rectal cancer, and where the cancer cannot be cured treatment aims to slow it, ease symptoms and help people live longer, with a palliative care team, NHS, colorectal cancer treatment. ↩
  42. On supplements during cancer treatment: the NIH National Center for Complementary and Integrative Health states that the effects of vitamin, mineral and antioxidant supplements during cancer treatment are uncertain, that they might interfere with chemotherapy or other cancer therapies, and that some herbal supplements may interact in harmful ways with drugs used in cancer treatment, so their use should be discussed with the treating team, NCCIH, cancer and complementary health approaches. ↩
  43. On follow-up after treatment: guidance endorsed by the American Society of Clinical Oncology advises a history, examination and CEA blood test every 3 to 6 months for 5 years, a chest and abdominal CT scan yearly for 3 years in most cases, and a colonoscopy 1 year after surgery and then about every 5 years depending on findings, along with a healthy body weight and an active lifestyle, PubMed 24220554. ↩
  44. On bleeding that is an emergency: US guidance advises calling emergency services or going to an emergency room for black, tarry stools, a lot of blood in the stool, vomiting blood or material like coffee grounds, feeling lightheaded or dizzy from bleeding, or severe abdominal pain with bleeding, MedlinePlus, gastrointestinal bleeding. ↩
  45. On abdominal pain that is an emergency: NHS guidance advises calling emergency services or going to an emergency department if abdominal pain comes on very suddenly or is severe, or if you cannot pass stool or gas, NHS, stomach ache; the symptoms of a blocked bowel include abdominal pain and cramping, swelling, inability to pass gas, nausea and vomiting, MedlinePlus, intestinal obstruction. ↩
  46. On fever during chemotherapy: NHS guidance advises calling your care team at once for a high temperature, with signs such as feeling hot, cold, sweaty or shivery, or other signs of infection, NHS, chemotherapy side effects; the National Cancer Institute lists a fever of 100.5°F (38°C) or higher and chills among the signs of infection during cancer treatment, NCI, infection and neutropenia. ↩
  47. Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of long-term marine omega-⁠3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation. 2021;144(25):1981-⁠1990. PubMed 34612056. Seven trials with 81,210 people followed for about 5 years: omega-⁠3 supplements were linked to a higher risk of atrial fibrillation (hazard ratio 1.25), more so in trials of more than 1 g a day (1.49), and the risk rose with each additional gram. ↩
  48. Ng K, Nimeiri HS, McCleary NJ, et al. Effect of high-dose vs standard-dose vitamin D3 supplementation on progression-free survival among patients with advanced or metastatic colorectal cancer: the SUNSHINE randomized clinical trial. JAMA. 2019;321(14):1370-⁠1379. PubMed 30964527. In 139 patients starting chemotherapy for advanced or metastatic colorectal cancer, median progression-free survival was 13.0 months on high-dose vitamin D3 against 11.0 months on standard dose, not a significant difference, though a supportive multivariable analysis favored high dose (hazard ratio 0.64). ↩
  49. Manson JE, Cook NR, Lee IM, et al. Marine n-⁠3 fatty acids and prevention of cardiovascular disease and cancer. N Engl J Med. 2019;380(1):23-⁠32. PubMed 30415637. In the VITAL trial, omega-⁠3 fatty acid supplements did not lower the incidence of invasive cancer against placebo (820 against 797 cases; hazard ratio 1.03). ↩