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).