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 about to enter 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.
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. No studies have shown that omega-3 can reduce these deposits.
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 psyhiatric 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 theoretically reduce cancer risk.
Heart Disease People who consume more omega-3 fatty acid supplementation have been shown to have fewer and less severe cardiovascular events such as heart attacks. 188 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 oil, 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.
Ulcerative Colitis Twenty four patients with ulcerative colitis participated in a study to see if omega-3 would be helpful in controlling the symptoms associated with this disease. Patients were randomized to receive either omega-3 rich oil, or corn oil for four months. One month following the initial treatment, patients received the opposite treatment for four more months. Patients taking the omega-3 fatty acid had improved symptom scores as well as weight gain when compared with the patients on the placebo.
High Cholesterol 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.
Cystic Fibrosis A systematic review of trials testing whether omega-3 fatty acid supplementation would benefit patients with cystic fibrosis. The researchers found two trials including a total of 31 participants. One of the studies showed improvement in a few respiratory measures such as forced expiratory volume and forced vital capacity.
Asthma A systematic review of trials of omega-3 fatty acids for asthma in participants over two years of age that were at least four weeks in duration. Researchers found nine trials. No consistent effect on most major asthma symptom measures was reported. One study which included other dietary changes did show an improvement of peak flow and a reduction in asthma medication use, however, researchers cannot determine if omega-3 fatty acids contributed at all to that outcome. Researchers conclude that little evidence supports using omega-3 fatty acids to improve asthma control.
Schizophrenia A systematic review of trials of polyunsaturated fatty acids for schizophrenia evaluated five small, short studies including 313 participants. One small study suggested that eicosapentaenoic enriched oil may have some antipsychotic properties when compared with placebo. Most trials, however, were too small to show any significant effects. Some of the trials included other fatty acids besides omega-3. Researchers conclude that larger, well designed studies are needed.
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.
This product is regulated by the FDA as a dietary supplement. Unlike approved drugs, supplements are not required to be manufactured under specific standardized conditions. The product may not contain the labeled amount or may be contaminated. In addition, it may not have been tested for safety or effectiveness.
Omega-3 polyunsaturated fatty acids should not be confused with omega-6 polyunsaturated fatty acids, such as those found in evening primrose oil and borage oil, which do not have the same effects in the body.
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). Studies of omega-3 fatty acid supplementation and cognition in young children (6) and elderly subjects (7) are inconclusive. Omega-3 fatty acid supplementation lowered cholesterol (8)(33) and may reduce recurrence in patients with history of stroke (32) ; however, low density lipoprotein cholesterol levels were increased (9). They may also help patients with ulcerative colitis (10), but were ineffective for 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 lower the magnitude of the body's inflammatory response (18) and can reduce sunburn sensitivity (20). Reviews of trials using omega-3 fatty acids have shown possible benefits for patients with cystic fibrosis (21), but no benefit for patients with asthma (22). Results from a recent clinical trial suggest that dietary supplementation with fish oil may help reduce the symptoms of systemic lupus erythematosus (24).
The role of omega-3 fatty acids in cancer prevention is inconclusive. Omega-3 fatty acids may reduce colon cancer risk (11) and may also improve the immune response in patients undergoing colorectal cancer resection (12). But a systematic review of studies did not find a significant effect of omega-3 fatty acid consumption on cancer incidence (15), although data from a prospective study suggest an association between fatty fish consumption and reduced occurrence of renal cell carcinoma in women (16). Conflicting results from another study point to increased risk of advanced prostate cancer with higher intake of alpha-linolenic acid in patients with low grade cancer (17). Further studies are warranted.
Omega-3 fatty acids are thought to have anticoagulant effects. But studies show that they do not affect coagulation and platelet function post surgery (19).
Omega-3 fatty acids are a type of polyunsaturated fatty acid 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 come from its ability to be incorporated into and thereby enhance the stability of atherosclerotic plaques (26). Omega-3 fatty acid does not seem to affect platelet function or coagulation (19). 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 its anti-inflammatory effects, omega-3 fatty acids have been thought to benefit patients with asthma (22) and cystic fibrosis (21); however, studies 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).
Gunnarsdottir I, et al. Inclusion of fish or fish oil in weight-loss diets for young adults: effects on blood lipids. Int J Obes. Jul 2008;32(7):1105-1112. The effect of various fish oils (supplements versus fish diets) on blood lipid profiles in young, overweight adults during weight loss was assessed in this randomized, controlled study. Three hundred twenty-four participants on an energy-restricted diet were randomly divided into 4 groups receiving 1) sunflower oil control capsules, 2) cod (lean fish) diet, 3) salmon (oily fish) diet, or 4) fish oil capsules. After 8 weeks, triglyceride reduction was greater in participants, receiving the cod diet, salmon diet, and fish oil as compared to the control group. With respect to total cholesterol, participants receiving the cod and salmon diets experienced greater reductions while the placebo group and those receiving fish oil supplements had similar cholesterol levels. Further studies of whole fish are necessary to determine the effect of fish constituents such as omega-3 fatty acids on blood lipid concentrations.
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.
Woods RK, Thien FC, Abramson MJ. Dietary marine fatty acids (fish oil) for asthma in adults and children. Cochrane.Database.Syst.Rev. 2002;CD001283. A systematic review of trials of omega-3 fatty acids for asthma in participants over two years of age that were at least four weeks in duration. The review included nine trials. No consistent effect on any of the following outcomes was observed: FEV1, peak flow rate, asthma symptoms, asthma medication use or bronchial hyper reactivity. One study which combined dietary manipulation with fish oil supplementation demonstrated improvement in peak flow and a reduction in asthma medication use, however the researchers concluded that there is little evidence to recommend omega-3 fatty acids to improve asthma control. No adverse effects were reported.
Joy CB, Mumby-Croft R, Joy LA. Polyunsaturated fatty acid supplementation for schizophrenia. Cochrane.Database.Syst.Rev. 2003;CD001257. A systematic review of trials of polyunsaturated fatty acids for schizophrenia included including five small, short studies including 313 participants. One small study suggested that EPA enriched oil may have some antipsychotic properties when compared with placebo, however most trials were too small to show significant effect. Some of the trials included omega-6 fatty acid supplementation. Researchers conclude that larger, well designed studies are needed.
