For Patients & Caregivers

How It Works

Omega-3 fatty acids have not been shown to prevent cancer.

Omega-3 fatty acids are obtained from fish oil. They have been used to protect against cardiovascular events such as heart attack. Studies have shown that omega-3 fatty acids can be taken up by the fatty deposits that line the arteries, thereby improving the stability of those deposits. Omega-3 fatty acids do not seem to affect the clotting of blood. Omega-3 fatty acids may reduce inflammation by decreasing some of the signals that cells send to each other. It is thought that patients with colitis, asthma, cystic fibrosis and those before surgery may benefit from this reduced inflammatory effect. Omega-3 fatty acid supplements have been shown to be absorbed by the skin and protect it against ultra-violet radiation damage.

Omega-3 fatty acids may reduce the risk of breast cancer, but may increase the risk of prostate cancer.

Purported Uses

  • To treat asthma
    A review of published trials shows no effect of omega-3 on asthma.
  • To treat fatty deposits on the inside of arteries (atherosclerosis)
    Studies have shown that omega-3 can increase the stability of these deposits, which may make them less dangerous.
  • To protect against cardiovascular disease
    Studies have shown that omega-3 can reduce the frequency and severity of cardiovascular events such as heart attacks.
  • To improve the symptoms of colitis
    Studies have shown that omega-3 may improve the symptoms associated with colitis.
  • To alleviate the symptoms associated with cystic fibrosis
    One study showed an improvement in breathing parameters for patients taking omega-3 supplements, however other trials have shown no benefit. Larger studies are necessary to determine the actual effect.
  • To treat symptoms of lupus
    A small study found a reduction in symptoms of lupus in patients who took fish oil compared with those on placebo. More trials are needed to support this claim.
  • To alleviate depression
    A study of a few thousand people in Finland found that people who ate less fish were more likely to have the symptoms of depression than those who ate more fish. Other studies have also shown a connection between omega-3 levels and depression scores, however few studies have attempted to determine if omega-3 supplementation affects depression symptoms.
  • To lower cholesterol levels
    A review of published trials of omega-3 for lowering cholesterol levels in patients with diabetes found that while omega-3 lowered triglyceride levels, it also raised LDL cholesterol levels.
  • To treat psychiatric disorders
    A recent study showed that omega-3 may be useful in reducing the risk of progression to psychiatric disorders.
  • To protect the skin against ultra-violet radiation damage.
    Studies have shown omega-3 to be incorporated into the skin and offer protection against UV damage which may reduce cancer risk.
  • To prevent cancer
    Omega-3 fatty acids may reduce the risk of breast cancer, but may increase the risk of prostate cancer.

Do Not Take If

  • You are taking nonsteroidal anti-inflammatory drugs (NSAIDs): Fish oil can have additive anticoagulant/antiplatelet effects.
  • You are taking glucocorticoids: Omega-3 supplements can worsen some side effects caused by glucocorticoids.
  • You are using platinum-based chemotherapy drugs: Fish oil may affect their activities.

Side Effects

  • Fishy aftertaste
  • Loose stool
  • Nausea

Special Point

Omega-3 fatty acids should not be confused with omega-6 fatty acids, such as those found in evening primrose oil and borage oil, which have different effects in the body.

Back to top

For Healthcare Professionals

Brand Name

Omegaven®, Max-EPA

Clinical Summary

A type of polyunsaturated fatty acid (PUFA) derived mainly from fish oil, omega-3 fatty acids are used as a dietary supplement for depression, to lower cholesterol, and to reduce the risk of heart attack. A large survey of Finnish adults found that depressive symptoms were significantly higher among infrequent fish consumers (1) and other studies have shown that individuals with major depression have marked depletions in omega-3 fatty acids (2). However, omega-3 fatty acid supplementation did not relieve depression in adults with major depression (3), mild to moderate depression (4), or perinatal depression (5), and yielded mixed results in those with schizophrenia (23). But data from a randomized trial suggest that omega-3 may be useful in reducing the risk of progression to psychiatric disorders and as a safe preventive measure in young adults at risk for psychotic conditions (35).

Supplementation with docosahexaenoic acid (DHA) improved learning and memory function in age related cognitive decline (41). However, consumption of fish oil during pregnancy does not improve cognitive or language outcomes in newborns (37) and does not improve intelligence (42). Studies of omega-3 fatty acid supplementation and cognition in young children (6) and elderly subjects (7) are inconclusive.

Omega-3 fatty acid supplementation lowers cholesterol (8) (33) and may reduce recurrence in patients with a history of stroke (32). However, it does not lower the risk of cardiovascular disease events (9). Omega-3 may help patients with ulcerative colitis (10), but was ineffective in the treatment of Crohn’s disease (13). In adults with rheumatoid arthritis, reductions in NSAID use were reported after omega-3 fatty acid supplementation (14); Omega-3 may also be effective in reducing NSAID-associated gastroduodenal damage (47). Other studies indicate that omega-3 may lower the magnitude of the body’s inflammatory response (18), and can reduce sensitivity to sunburn (20) and to ultraviolet radiation (44). Reviews of trials using omega-3 fatty acids have shown possible benefits for patients with cystic fibrosis (21), but no benefit in those with asthma (22). Dietary supplementation with fish oil may help reduce the symptoms of systemic lupus erythematosus (24). Findings of a systematic review support benefits of polyunsaturated omega-3 fatty acid consumption on insulin sensitivity and adipocyte function (45). In another study, DHA was found more effective compared to eicosapentanoic acid (EPA) in modulating indicators of inflammation and blood lipids (50).

Data on omega-3 fatty acid supplementation for cancer prevention are inconclusive. It may reduce colon cancer risk (11) and improve immune response in patients undergoing colorectal cancer resection (12), but did not affect cancer outcomes (15) (43), although data from a prospective study suggest its association with reduced occurrence of renal cell carcinoma in women (16). Fish oil supplementation may lower the risk of breast cancer (36). However, high blood concentrations of omega-3 is associated with increased risk of prostate cancer (17).

Preliminary findings suggest benefits of fish oil supplementation in increasing efficacy of chemotherapy, improving survival (38), and for maintenance of weight and muscle mass (39) in patients with nonsmall cell lung cancer (NSCLC). An EPA-enriched oral supplement improved tolerability of chemotherapy in patients with advanced colorectal cancer (40). And, when combined with chemotherapy, fish oil supplementation may delay tumor progression in patients with colorectal cancer (49). However, according to a recent study, a type of omega-3 fatty acid, 16:4(n-3), can reduce the activity of cisplatin (48).

Omega-3 fatty acids are thought to have anticoagulant effects. However, results from clinical studies are mixed  (19) (51).

Food Sources

  • Fish Oil
  • Krill Oil
  • Cod Liver Oil
  • Flaxseed Oil
  • Linseed Oil

Purported Uses

  • Asthma
  • Atherosclerosis
  • Cancer prevention
  • Cardiovascular disease
  • Colitis
  • Cystic fibrosis
  • Depression
  • High cholesterol
  • Lupus symptoms
  • Schizophrenia

Mechanism of Action

Omega-3 fatty acids are polyunsaturated fatty acids containing two or more double bonds in their acyl chain and a double bond on carbon number (3) (26). Changes in omega-3 fatty acid blood levels have been associated with cardiovascular disease and depression (27). The cardioprotective effects of omega-3 fatty acids likely are due its ability to be incorporated into and thereby enhance the stability of atherosclerotic plaques (26). Increasing the intake of polyunsaturated fatty acids has been shown to increase lipid peroxidation. Supplementation with omega-3 fatty acids, therefore, may increase oxidative stress on the body. Studies have shown that mucosal alpha-tocopherol levels decrease upon omega-3 fatty acid supplementation, which researchers believe may result from the body’s attempt to counteract the added oxidative burden (11). Besides reducing serum antioxidant levels, little is known about how this added oxidative stress affects the body.

Omega-3 fatty acid supplementation has been shown to decrease IL-6 (18) and tumor necrosis factor-alpha (28) levels while leaving most other mononuclear cell functions unaffected (29). Omega-3 fatty acids may also reduce inflammation in patients with ulcerative colitis by reducing rectal dialysate leukotriene B4 (10). Because of their anti-inflammatory effects, omega-3 fatty acids were thought to benefit patients with asthma (22) and cystic fibrosis (21), but data are inconclusive.

Increasing PUFA intake in pregnant women increases PUFA concentration but not cytokine concentration in human milk (30). Omega-3 fatty acid supplementation provides protection against ultra-violet radiation-induced erythema and p53 expression, a biomarker of DNA damage (20).

Adverse Reactions

Fishy aftertaste (11) and loose stools and nausea (31) have been reported following intake of large doses of omega-3 fatty acids.

Herb-Drug Interactions

  • Nonsteroidal Anti-inflammatory drugs (NSAIDS): Fish oil can have additive anticoagulant/antiplatelet effects (34).
  • Glucocorticoids: Omega-3 supplementation may potentiate some of the adverse effects of glucocorticoids (46).
  • Platinum compounds: One study shows fish oil supplementation may increase the efficacy of carboplatin-based chemotherapy regimen (38). Another study finds omega-3 fatty acid, 16:4(n-3), may reduce the activity of cisplatin (48).

Herb Lab Interactions

  • May reduce levels of alpha-tocopherol and beta-carotene (11) (28).
  • High levels of omega-3 fatty acids may decrease triglyceride and increase LDL cholesterol levels (9).
  • Doses higher than 3 grams per day may increase bleeding time (25).

Dosage (OneMSK Only)


  1. Tanskanen A, Hibbeln JR, Tuomilehto J, Uutela A, Haukkala A, Viinamaki H et al. Fish consumption and depressive symptoms in the general population in Finland. Psychiatr.Serv. 2001;52:529-31.

  2. Mischoulon D,.Fava M. Docosahexanoic acid and omega-3 fatty acids in depression. Psychiatr. Clin North Am 2000;23:785-94.

  3. Grenyer BF, Crowe T, Meyer B, et al. Fish oil supplementation in the treatment of major depression: a randomised double-blind placebo-controlled trial. Prog Neuropsychopharmacol Biol Psychiatry 2007 Oct 1;31(7):1393-6.

  4. Rees AM, Austin MP, Parker GB. Omega-3 fatty acids as a treatment for perinatal depression: randomized double-blind placebo-controlled trial. Aust N Z J Psychiatry. 2008 Mar;42(3):199-205

  5. van de Rest O, Geleijnse JM, Kok FJ, et al. Effect of fish oil on cognitive performance in older subjects: a randomized, controlled trial. Neurology 2008 Aug 5;71(6):430-8.

  6. Stenson WF, Cort D, Rodgers J, Burakoff R, DeSchryver-Kecskemeti K, Gramlich TL et al. Dietary supplementation with fish oil in ulcerative colitis. Ann.Intern.Med 1992;116:609-14.

  7. Anti M, Armelao F, Marra G, Percesepe A, Bartoli GM, Palozza P et al. Effects of different doses of fish oil on rectal cell proliferation in patients with sporadic colonic adenomas. Gastroenterology 1994;107:1709-18.

  8. Feagan BG, Sandborn WJ, Mittmann U, et al. Omega-3 free fatty acids for the maintenance of remission in Crohn disease: the EPIC Randomized Controlled Trials. JAMA 2008 Apr 9;299(14):1690-7.

  9. MacLean CH, et al. Effects of Omega-3 Fatty Acids on Cancer Risk. JAMA 2006; 295(4).

  10. Wolk A, Larsson SC, Johansson J, Ekman P. Long-term fatty fish consumption and renal cell carcinoma incidence in women. JAMA 2006;296(11):1371-1376.

  11. Brasky TM, Darke AK, Song X, et al. Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial. J Natl Cancer Inst. 2013 Aug 7;105(15):1132-41.

  12. Weiss G, Meyer F, Matthies B, Pross M, Koenig W, Lippert H. Immunomodulation by perioperative administration of n-3 fatty acids. Br J Nutr 2002;87 Suppl 1:S89-S94.

  13. Heller AR, Fischer S, Rossel T, Geiger S, Siegert G, Ragaller M et al. Impact of n-3 fatty acid supplemented parenteral nutrition on haemostasis patterns after major abdominal surgery. Br J Nutr 2002;87 Suppl 1:S95-101.

  14. Rhodes LE, Shahbakhti H, Azurdia RM, Moison RM, Steenwinkel MJ, Homburg MI et al. Effect of eicosapentaenoic acid, an omega-3 polyunsaturated fatty acid, on UVR-related cancer risk in humans. An assessment of early genotoxic markers. Carcinogenesis 2003;24:919-25.

  15. Beckles WN, Elliott TM, Everard ML. Omega-3 fatty acids (from fish oils) for cystic fibrosis. Cochrane.Database.Syst.Rev. 2002;CD002201.

  16. Woods RK, Thien FC, Abramson MJ. Dietary marine fatty acids (fish oil) for asthma in adults and children. Cochrane.Database.Syst.Rev. 2002;CD001283.

  17. Joy CB, Mumby-Croft R, Joy LA. Polyunsaturated fatty acid supplementation for schizophrenia. Cochrane.Database.Syst.Rev. 2003;CD001257.

  18. Lewis, C. J. Letter Regarding Dietary Supplement Health Claim for Omega-3 Fatty Acids and Coronary Heart Disease. FDA Docket No. 91N-0103. 10-31-2000. Accessed July 25, 2014.

  19. Thies F, Garry JM, Yaqoob P, Rerkasem K, Williams J, Shearman CP et al. Association of n-3 polyunsaturated fatty acids with stability of atherosclerotic plaques: a randomised controlled trial. Lancet 2003;361:477-85.

  20. Holm T, Berge RK, Andreassen AK, Ueland T, Kjekshus J, Simonsen S et al. Omega-3 fatty acids enhance tumor necrosis factor-alpha levels in heart transplant recipients. Transplantation 2001;72:706-11.

  21. Fugh-Berman A, Cott JM. Dietary supplements and natural products as psychotherapeutic agents. Psychosom.Med 1999;61:712-28.

  22. Gunnarsdottir I, Tomasson H, Kiely M, et al. Inclusion of fish or fish oil in weight-loss diets for young adults: effects on blood lipids. Int J Obes. 2008;32(7):1105-12.

  23. Haller C, Kearney T, Bent S, et al. Dietary supplement adverse events: report of a one-year poison center surveillance project. J Med Toxicol. 2008 Jun;4(2):84-92.

  24. Amminger GP, Schäfer MR, Papageorgiou K, et al. Long-Chain {omega}-3 Fatty Acids for Indicated Prevention of Psychotic Disorders: A Randomized, Placebo-Controlled Trial. Arch Gen Psychiatry. 2010 Feb;67(2):146-54.

  25. Brasky TM, Lampe JW, Potter JD, Patterson RE, White E. Specialty Supplements and Breast Cancer Risk in the VITamins And Lifestyle (VITAL) Cohort. Cancer Epidemiol Biomarkers Prev. 2010;19(7); 1696-708.

  26. Makrides M, Gibson R,McPhee A, et al. Effect of DHA Supplementation During Pregnancy on Maternal Depression and Neurodevelopment of Young Children. A Randomized Controlled Trial. JAMA. 2010;304(15):1675-1683.

  27. Campoy C, Escolano-Margarit MV, Ramos R, et la. Effects of prenatal fish-oil and 5-methyltetrahydrofolate supplementation on cognitive development of children at 6.5 y of age. Am J Clin Nutr. 2011; 94(6 Suppl):1880S-1888S.

  28. Wu JH, Cahill LE, Mozaffarian D. Effect of Fish Oil on Circulating Adiponectin: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Clin Endocrinol Metab. 2013 Jun;98(6):2451-9.

  29. Fappi A, Godoy TS, Maximino JR, et al. The effects of omega-3 Fatty Acid supplementation on dexamethasone-induced muscle atrophy. Biomed Res Int. 2014;2014:961438.

  30. Park JM, Han YM, Jeong M, et al. Omega-3 polyunsaturated acids as an angelus custos to rescue patients from NSAID-induced gastroduodenal damage. J Gastroenterol. 2015 Jan 13. [Epub ahead of print]

  31. Daenen L, Geert A. Cirkel G, Houthuijzen M, et al. Increased Plasma Levels of Chemoresistance-Inducing Fatty Acid 16:4(n-3) After Consumption of Fish and Fish Oil. JAMA Oncol. 2015 Jun;1(3):350-8.

  32. Camargo Cde Q, Mocellin MC, Pastore Silva Jde A, Fabre ME, Nunes EA, Trindade EB. Fish oil supplementation during chemotherapy increases posterior time to tumor progression in colorectal cancer. Nutr Cancer. 2016;68(1):70-6.

Back to top
Back to top
Email your questions and comments to

Last Updated