For Patients & Caregivers
Bottom Line: 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 acid may reduce the risk of breast cancer, but may increase the risk of prostate cancer.
- 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 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 acid may reduce the risk of breast cancer, but may increase the risk of prostate cancer.
People who consume more omega-3 fatty acid supplementation have been shown to have fewer and less severe cardiovascular events such as heart attacks. One hundred and eighty-eight patients awaiting endarterectomy (the surgical removal of the inner lining of a clogged artery) took part in a trial to determine how omega-3 produces these effects. Patients were randomized to receive either fish oil, which is high in omega-3 fatty acids, sunflower oil, which is high in a different kind of fatty acids or a control, which contained the same proportion of fatty acids that people typically eat on a daily basis. Patients consumed 6 grams of oil and 6 milligrams of alpha-tocopherol, an antioxidant, per day for an average duration of 42 days. Patients who consumed the fish oil were found to have incorporated the omega-3 fatty acids into the plaques on their arteries which enhanced the stability of these plaques. Patients receiving sunflower oil or the control oil did not experience a change in their plaques. Researchers believe that increasing the stability of the plaques on the walls of the arteries reduces the chances that some of the plaque will break off and lead to a heart attack. It appears that this phenomenon explains why omega-3 may help protect against heart attacks.
Systemic Lupus Erythematosus
Fifty two patients participated in a recent clinical trial performed to assess the beneficial effects of dietary supplementation with omega-3 fish oils and copper. Patients were randomly assigned to receive fish oil and placebo copper, fish oil and copper, copper and placebo fish oil, and the last group received both placebo capsules. Researchers found a reduction in symptoms of SLE in patients who took fish oil compared to those on placebo. The effect of copper was not significant. Since the number of patients in the trial is small, more trials are needed to support this claim.
A systematic review of studies that use fish oil to reduce cholesterol levels in people with type 2 diabetes mellitus. The researchers analyzed the results of 18 trials including 823 participants. Analysis of the data showed that fish oil was able to reduce triglycerides, however it increased low density lipoprotein (LDL or ’bad’ cholesterol) levels. Fish oil supplementation did not affect glucose levels or the level of high density lipoprotein (HDL or ’good’ cholesterol). Researchers also observed that while no adverse effects were reported, no trials attempted to determine if the fish oil supplementation would produce serious adverse effects.
- 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.
For Healthcare Professionals
A type of polyunsaturated fatty acid (PUFA) derived mainly from fish oil, omega-3 fatty acids are used as 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 a 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 of the kids (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 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, reduction in NSAID use was 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).
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 concentration of omega-3 is associated with increased risk of prostate cancer (17). Further studies are needed.
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 eicosapentanoic acid (EPA)-enriched oral supplement improved tolerability of chemotherapy in patients with advanced colorectal cancer (40). However, another study finds a type of omega-3 fatty acid, 16:4(n-3), may reduce the activity of cisplatin (48).
Omega-3 fatty acids are thought to have anticoagulant effects. But studies show that they do not affect coagulation or platelet function after surgery (19).
Fatty Acids: Eicosapentanoic (EPA), Docosahexanoic (DHA), Myristic, Palmitic, Palmitoleic, Stearic, Oleic, Linoleic, Linolenic, Stearidonic, Eicosanoic, Arachidonic, Docosanoic and docosapentanoic (DPA) (19)
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 the 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 anti-oxidant 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); however, 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).
- 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).
Tanaka K, et al. Reduction in the recurrence of stroke by eicosapentaenoic acid for hypercholesterolemic patients: subanalysis of the JELIS trial. Stroke. 2008;39(7):2052-2058.
The JELIS trial was a large, prospective, clinical-controlled trial of 18,645 hypercholesterolemic patients that received statin therapy with or without omega-3 fatty acid supplementation (1800 mg/day). While stroke incidence during the 4.6 year mean follow-up period was not affected by omega-3 fatty acid supplementation in patients without a history of stroke, stroke recurrence was significantly reduced in individuals with a history of stroke. Due to the open-label design of this study, further studies are required.
Duffy EM et al. The clinical effect of dietary supplementation with omega-3 fish oils and/or copper in systemic lupus erythematosus. J. Rheumatology. 2004;31(8):1551-6.
A double blind, double placebo controlled trial. Fifty-two SLE patients were randomly assigned to 4 treatment groups that received 3 g fish oil and 3 g of copper, 3 g fish oil and placebo copper, 3 g copper and 3 g placebo fish oil, or both placebo capsules. Researchers found a significant reduction in symptoms of SLE in patients who took fish oil capsules compared to those on placebo. There was no measurable effect on symptoms in patients who took copper. Larger trials are needed to support this claim.
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.
A randomized controlled trial of polyunsaturated fatty acids and stability of atherosclerotic plaques. 188 patients awaiting carotid endarterectomy were randomized to receive sunflower oil (high omega-6 concentration), fish oil (high omega-3 concentration) or control oil until surgery. Each patient consumed six capsules per day each containing 1 g of oil and 1 mg alpha-tocopherol. Duration of treatment ranged from seven to 189 days with a median of 42 days. Patients receiving the fish oil supplementation were found to have readily incorporated omega-3 polyunsaturated fatty acids in their atherosclerotic plaques thereby enhancing the stability of the plaques. Patients receiving either sunflower oil or control had no change in fatty-acid composition or atherosclerotic stability during the course of treatment. Researchers believe that this stability of plaques may explain the reductions in cardiovascular events associated with omega-3 polyunsaturated fatty acid intake.