Colorectal cancer is the third leading cause of cancer death for American men and women alike … and the disease kills nearly one in three people diagnosed with it.
The National Cancer Institute estimates 143,460 new diagnoses in 2012 … and that colorectal cancers will kill 51,690 Americans this year, with most deaths occurring after age 65.
These statistics help explain why – despite increasing rates of colonoscopies – colorectal cancer remains a leading cancer threat.
A large body of evidence indicates that lifestyle factors influence the risk and progress of colorectal cancers … and lab studies provide possible reasons for those associations.
Epidemiological studies link high intakes of red and processed meat (more than 18 ounces a week) or alcohol (more than two drinks a day) to a higher risk for colorectal cancer.
How much fish does it take?
If fish really helps curb colorectal cancer – and we’d need more clinical evidence to prove that – how much fish does it take to lower the risk?
Frankly, it’s impossible to say, since the ranges of intake for “low” and “high” consumers of fish varied substantially across the included studies … and because fish vary widely in their omega-3 content.
However, the studies provide enough data to suggest that it’s wise to enjoy at least two servings of fatty fish a week.
Fish that offer the most omega-3 fatty acids include salmon, tuna, sablefish, mackerel, blue fish, sardines, and anchovies. (See our Seafood Nutrition Chart.)
And, based on the pilot clinical studies mentioned here, it appears that a daily fish oil supplement may offer substantial colorectal benefits … although that remains uncertain.
Whether the beneficial effects of fish stem solely from omega-3 fatty acids or partly from other nutrients found in fish – such as selenium and vitamin D – is unproven.
Conversely, the epidemiological evidence generally links exercise, lower body mass, and diets higher in fiber, calcium, or magnesium to a lower risk for colorectal cancer.
And growing evidence suggests that the omega-3 fatty acids in fish may help protect against colorectal cancers.
Omega-3s and colon health: The story so far
People who eat lots of fish – such as Swedish fisher-folk and people living in Finland – enjoy very low rates of colorectal cancer … compared with places where fish is an infrequent item on the home menu.
However, although some studies have shown an inverse relationship between fish consumption and colorectal cancer, others have not.
Consequently, the association between fish consumption and the risk of colorectal cancer has been unclear.
Omega-3 fats from fish (EPA and DHA) have reduced the size and number of colorectal cancer cells in animal studies (Calviello G et al. 1999).
Earlier this year, researchers at Tennessee’s Vanderbilt-Ingram Cancer Center (VICC) reported that women who averaged three 3.5 ounce servings of fish a week – versus less than half a serving – were one-third less likely to develop colorectal polyps with cancerous potential (adenomas) … see “Female Fish-Lovers had Fewer Colon Polyps.”
Possible reasons include the anti-inflammatory actions of omega-3s – especially omega-3 EPA, which was used in the UK trial and has produced anti-inflammatory effects in the colon tissues of children with ulcerative colitis (Shimizu T et al. 2003).
(Of course, people who eat lots of fish tend to eat less red and processed meats, which are linked to increased colorectal cancer risk.)
Now, a Chinese team’s review of the available epidemiological evidence suggests that people who eat fish often are significantly less likely to develop colorectal cancer.
This new review did not include the Tennessee study, presumably because it was published pretty recently … which means that the risk reduction may be a bit greater than the Chinese team calculated.
Chinese study finds most studies link fish to lower colon risk
The new evidence review comes from researchers at the Fourth Military Medical University (FMMU) in Xi'an, China … one of China’s leading biomedical research centers (Wu S et al. 2012).
The Chinese team pooled results from 41 studies that measured fish intake, tracked cancer diagnoses, and accounted for factors known to influence the risk of colorectal cancer risk … family history, body weight, physical activity, smoking, alcohol use, and various dietary factors.
(The studies came from the U.S., Canada, Britain, Australia, Italy, Japan, China, Norway, Finland, Sweden, and the Netherlands.)
Encouragingly, people who ate fish regularly were 12 percent less likely to be diagnosed with any kind of colorectal cancer.
The protective effect was strongest for rectal cancer. Compared to participants who reported eating the least fish, those who reported eating the most fish were 21 percent less likely to have developed rectal cancer.
Obviously, we'll need substantial clinical evidence to prove that fish and/or supplemental omega-3s help prevent colorectal cancers.
But since it's clear that both support heart health, it only makes sense to shift the protein part of your diet in favor of fatty fish, in the wholly realistic hope that this move will deliver myriad benefits.
Albanes D, Virtamo J. Diet and risk of colorectal cancer in a cohort of Finnish men. Cancer Causes and Control. 1999;10:387-396.
Anti M, Armelao F, Marra G, Percesepe A, Bartoli GM, Palozza P, Parrella P, Canetta C, Gentiloni N, De Vitis I, et al. Effects of different doses of fish oil on rectal cell proliferation in patients with sporadic colonic adenomas. Gastroenterology. 1994 Dec;107(6):1709-18.
Benito E, Obrador A, Stiggelbout A, et al. A population-based casecontrol study of colorectal cancer in Majorca. I. Dietary factors. Int J Cancer. 1990;45:69-76.
Bidoli E, Franceschi S, Talamini R, et al. Food consumption and cancer of the colon and rectum in north-eastern Italy. Int J Cancer. 1992;50:223-229.
Calviello G, Palozza P, Maggiano N, Piccioni E, Franceschelli P, Frattucci A, Di Nicuolo F, Bartoli GM. Cell proliferation, differentiation, and apoptosis are modified by n-3 polyunsaturated fatty acids in normal colonic mucosa. Lipids. 1999 Jun;34(6):599-604.
Chan DS, Lau R, Aune D, Vieira R, Greenwood DC, Kampman E, Norat T. Red and processed meat and colorectal cancer incidence: meta-analysis of prospective studies. PLoS One. 2011;6(6):e20456. Epub 2011 Jun 6.
Courtney ED, Matthews S, Finlayson C, Di Pierro D, Belluzzi A, Roda E, Kang JY, Leicester RJ. Eicosapentaenoic acid (EPA) reduces crypt cell proliferation and increases apoptosis in normal colonic mucosa in subjects with a history of colorectal adenomas. Int J Colorectal Dis. 2007 Jan 10; [Epub ahead of print]
Kampman E, Verhoeven D, Sloots L, et al. Vegetable and animal products as determinants of colon cancer risk in Dutch men and women. Cancer Causes Control. 1995;6:225-234.
Kato I, Akhmedkhanov A, Koenig K, et al. Prospective study of diet and female colorectal cancer: the New York University Women’s Health Study. Nutr Cancer. 1997;28:276-281.
Mikoczy Z, Rylander L. Mortality and cancer incidence in cohorts of Swedish fishermen and fishermen’s wives: updated findings. Chemosphere. 2009;74:938-943.
Norat T, Bingham S, Ferrari P, et al. Meat, fish, and colorectal cancer risk: the European Prospective Investigation into cancer and nutrition. J Natl Cancer Inst. 2005;97:906-916.
Pauwels EK, Kairemo K. Fatty acid facts, part II: role in the prevention of carcinogenesis, or, more fish on the dish? Drug News Perspect. 2008 Nov;21(9):504-10. Review.
Peters RK, Pike M, Garabrant D, et al. Diet and colon cancer in Los Angeles County, California. Cancer Causes Control. 1992;3:457-473.
Sala-Vila A, Calder PC. Update on the relationship of fish intake with prostate, breast, and colorectal cancers. Crit Rev Food Sci Nutr. 2011 Oct-Nov;51(9):855-71. Review.
Shimizu T, Fujii T, Suzuki R, Igarashi J, Ohtsuka Y, Nagata S, Yamashiro Y. Effects of highly purified eicosapentaenoic acid on erythrocyte fatty acid composition and leukocyte and colonic mucosa leukotriene B4 production in children with ulcerative colitis. J Pediatr Gastroenterol Nutr. 2003 Nov;37(5):581-5.
Szymanski KM, Wheeler DC, Mucci LA. Fish consumption and prostate cancer risk: a review and meta-analysis. Am J Clin Nutr. 2010 Nov;92(5):1223-33. Epub 2010 Sep 15. Review.
Terry PD, Rohan TE, Wolk A. Intakes of fish and marine fatty acids and the risks of cancers of the breast and prostate and of other hormone-related cancers: a review of the epidemiologic evidence. Am J Clin Nutr. 2003 Mar;77(3):532-43. Review.
Tiemersma EW, Kampman E, Bueno de Mesquita HB, et al. Meat consumption, cigarette smoking, and genetic susceptibility in the etiology of colorectal cancer: results from a Dutch prospective study. Cancer Causes Control. 2002;13:383-393.
Wu S, Feng B, Li K, Zhu X, Liang S, Liu X, Han S, Wang B, Wu K, Miao D, Liang J, Fan D. Fish Consumption and Colorectal Cancer Risk in Humans: A Systematic Review and Meta-analysis. Am J Med. 2012 Apr 17. [Epub ahead of print]
Wu S, Liang J, Zhang L, Zhu X, Liu X, Miao D. Fish consumption and the risk of gastric cancer: systematic review and meta-analysis. BMC Cancer. 2011 Jan 20;11:26. Review.