Some research indicates that people who eat more seafood may have a reduced risk of cognitive decline. However, omega-3 supplements haven’t been shown to help prevent cognitive impairment or Alzheimer’s disease or to improve symptoms of these conditions. For example, a large NIH-sponsored study completed in 2015 indicated that taking EPA and DHA supplements did not slow cognitive decline in older adults. The people studied were participants in a larger eye disease study, and all of them had age-related macular degeneration (AMD). 
Omega-3 [(n-3)] long-chain PUFA, including EPA and DHA, are dietary fats with an array of health benefits (1). They are incorporated in many parts of the body including cell membranes (2) and play a role in antiinflammatory processes and in the viscosity of cell membranes (3, 4). EPA and DHA are essential for proper fetal development and healthy aging (5). DHA is a key component of all cell membranes and is found in abundance in the brain and retina (6). EPA and DHA are also the precursors of several metabolites that are potent lipid mediators, considered by many investigators to be beneficial in the prevention or treatment of several diseases (7).

A Cochrane meta-analysis published in June 2012 found no significant protective effect for cognitive decline for those aged 60 and over and who started taking fatty acids after this age. A co-author of the study said to Time, "Our analysis suggests that there is currently no evidence that omega-3 fatty acid supplements provide a benefit for memory or concentration in later life".[43]

Henriksen, C., Haugholt, K., Lindgren, M., Aurvag, A. K., Ronnestad, A., Gronn, M., Solberg, R., Moen, A., Nakstad, B., Berge, R. K., Smith, L., Iversen, P. O., and Drevon, C. A. Improved cognitive development among preterm infants attributable to early supplementation of human milk with docosahexaenoic acid and arachidonic acid. Pediatrics 2008;121(6):1137-1145. View abstract.
It helps maintain a good luster of the hair because omega-3 has growth stimulating properties since it provides nourishment to the follicles. It aids in the development of hair and in preventing hair loss. A good supply of protein is also necessary for hair growth, and since most fish varieties are rich in protein, eating fish helps to keep hair healthy.

Warfarin (Coumadin) is used to slow blood clotting. Fish oil also might slow blood clotting. Taking fish oil with warfarin might slow blood clotting too much and increase the risk of bleeding. However, conflicting results suggests that fish oil does not increase the effects of warfarin. Until more is known, use cautiously in combination with warfarin. Have your blood checked regularly, as your dose of warfarin (Coumadin) might need to be changed.

In 1964 it was discovered that enzymes found in sheep tissues convert omega−6 arachidonic acid into the inflammatory agent called prostaglandin E2[71] which both causes the sensation of pain and expedites healing and immune response in traumatized and infected tissues.[72] By 1979 more of what are now known as eicosanoids were discovered: thromboxanes, prostacyclins, and the leukotrienes.[72] The eicosanoids, which have important biological functions, typically have a short active lifetime in the body, starting with synthesis from fatty acids and ending with metabolism by enzymes. If the rate of synthesis exceeds the rate of metabolism, the excess eicosanoids may, however, have deleterious effects.[72] Researchers found that certain omega−3 fatty acids are also converted into eicosanoids, but at a much slower rate. Eicosanoids made from omega−3 fatty acids are often referred to as anti-inflammatory, but in fact they are just less inflammatory than those made from omega−6 fats. If both omega−3 and omega−6 fatty acids are present, they will "compete" to be transformed,[72] so the ratio of long-chain omega−3:omega−6 fatty acids directly affects the type of eicosanoids that are produced.[72]

During pregnancy and breastfeeding, eating 8 to 12 ounces per week of fish and other seafood may improve your baby’s health. However, it is important to choose fish that are higher in EPA and DHA and lower in mercury. Examples are salmon, herring, sardines, and trout. It is not clear whether taking dietary supplements containing EPA and DHA during pregnancy or breastfeeding affects a baby’s health or development. However, some studies show that taking these supplements may slightly increase a baby’s weight at birth and the length of time the baby is in the womb, both of which may be beneficial. Breast milk contains DHA. Most commercial infant formulas also contain DHA.
In some cases, fish oil pills may cause loose stools, nausea, diarrhea, and decreased appetite, fat in the stools, vomiting or constipation. These side effects can be minimized by taking a fish oil capsule that is coated, which is designed to help eliminate the "fish burps" many users complain about. Starting with low doses of the supplement and working up to a full dose can also help minimize side effects. You can also pair fish oil supplements with meals so that they enter your body more slowly, minimizing the risk of side effects occurring.
Dry eye disease occurs when tears don’t provide enough moisture, causing eye discomfort and vision problems. Some studies show that getting more omega-3s from foods or supplements—mainly EPA and DHA—helps relieve symptoms of dry eye disease. But a large, recent study found that the symptoms of people with dry eye disease who took fish oil supplements of 2,000 mg EPA plus 1,000 mg DHA daily for 1 year did not improve any more than those who took a placebo (a dummy pill). More research on the effects of omega-3s on dry eye disease is needed.
van der Meij, B. S., Langius, J. A., Smit, E. F., Spreeuwenberg, M. D., von Blomberg, B. M., Heijboer, A. C., Paul, M. A., and van Leeuwen, P. A. Oral nutritional supplements containing (n-3) polyunsaturated fatty acids affect the nutritional status of patients with stage III non-small cell lung cancer during multimodality treatment. J.Nutr. 2010;140(10):1774-1780. View abstract.
Higdon JV, Liu J, Du S, et al. Supplementation of postmenopausal women with fish oil rich in eicosapentaenoic acid and docosahexaenoic acid is not associated with greater in vivo lipid peroxidation compared with oils rich in oleate and linoleate as assessed by plasma malondialdehyde and F(2)- isoprostanes. Am J Clin Nutr 2000;72:714-22. View abstract.
McNamara, R. K., Able, J., Jandacek, R., Rider, T., Tso, P., Eliassen, J. C., Alfieri, D., Weber, W., Jarvis, K., DelBello, M. P., Strakowski, S. M., and Adler, C. M. Docosahexaenoic acid supplementation increases prefrontal cortex activation during sustained attention in healthy boys: a placebo-controlled, dose-ranging, functional magnetic resonance imaging study. Am J Clin Nutr 2010;91(4):1060-1067. View abstract.
EPA and DHA are vital nutrients and may be taken to maintain healthy function of the following: brain and retina: DHA is a building block of tissue in the brain and retina of the eye. It helps with forming neural transmitters, such as phosphatidylserine, which is important for brain function. DHA is found in the retina of the eye and taking DHA may be necessary for maintaining healthy levels of DHA for normal eye function.
Badia-Tahull, M. B., Llop-Talaveron, J. M., Leiva-Badosa, E., Biondo, S., Farran-Teixido, L., Ramon-Torrell, J. M., and Jodar-Masanes, R. A randomised study on the clinical progress of high-risk elective major gastrointestinal surgery patients treated with olive oil-based parenteral nutrition with or without a fish oil supplement. Br.J.Nutr. 2010;104(5):737-741. View abstract.

Your body can convert some ALA into EPA and then DHA, but not enough to meet all your body’s needs but the best way to assure you are getting enough heart healthy fats is to eat foods high in the omega 3 fats, and if you can’t or don’t get enough of these necessary fats in your diet, you might consider taking an omega 3 supplement to boost these needed fats. More on this later.

Your body can convert some ALA into EPA and then DHA, but not enough to meet all your body’s needs but the best way to assure you are getting enough heart healthy fats is to eat foods high in the omega 3 fats, and if you can’t or don’t get enough of these necessary fats in your diet, you might consider taking an omega 3 supplement to boost these needed fats. More on this later.

For those who do not eat seafood, another way exists for you to get a healthy dose of EPA and DHA each day. Fish oil supplements, which are rich in EPA and DHA, can be made from a variety of fish, with the most common ones being halibut, tuna, salmon, cod liver, mackerel and herring. On average, one 3.5 ounce serving of fatty fish contains about 1 gram of omega-3s, which can be obtained through fish oil supplements, according to MedlinePlus.

ACS Breast Cancer Screening Guideline CDC Guideline for Prescribing Opioids CDC Guideline for Prevention of Surgical Site Infections Consensus Definitions for Sepsis and Septic Shock Global Burden of Cancer, 1990-2016 Global Burden of Disease in Children, 1990-2013 Global Burden of Hypertension, 1990-2015 Global Firearm Mortality, 1990-2016 Health Care Spending in the US and Other High-Income Countries Income and Life Expectancy in the US JNC 8 Guideline for Management of High Blood Pressure President Obama on US Health Care Reform Screening for Colorectal Cancer Screening for Depression in Adults Screening for Prostate Cancer Statins for Primary Prevention of Cardiovascular Disease The State of US Health, 1990-2016 US Burden of Cardiovascular Disease, 1990-2016 WMA Declaration of Helsinki, 7th Revision
Conflicts of interest comprise financial interests, activities, and relationships within the past 3 years including but not limited to employment, affiliation, grants or funding, consultancies, honoraria or payment, speaker's bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued.
^ Jump up to: a b Casula M, Soranna D, Catapano AL, Corrao G (August 2013). "Long-term effect of high dose omega-3 fatty acid supplementation for secondary prevention of cardiovascular outcomes: A meta-analysis of randomized, placebo controlled trials [corrected]". Atherosclerosis. Supplements. 14 (2): 243–51. doi:10.1016/S1567-5688(13)70005-9. PMID 23958480.

FDA pregnancy category C. It is not known whether Fish Oil will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using Fish Oil. It is not known whether omega-3 polyunsaturated fatty acids pass into breast milk or if this could harm a nursing baby. Do not use Fish Oil without telling your doctor if you are breast-feeding a baby. Do not give this medication to anyone under 18 years old.
Joensen, A. M., Schmidt, E. B., Dethlefsen, C., Johnsen, S. P., Tjonneland, A., Rasmussen, L. H., and Overvad, K. Dietary intake of total marine n-3 polyunsaturated fatty acids, eicosapentaenoic acid, docosahexaenoic acid and docosapentaenoic acid and the risk of acute coronary syndrome - a cohort study. Br J Nutr 2010;103(4):602-607. View abstract.
Evidence suggests that omega−3 fatty acids modestly lower blood pressure (systolic and diastolic) in people with hypertension and in people with normal blood pressure.[25] Some evidence suggests that people with certain circulatory problems, such as varicose veins, may benefit from the consumption of EPA and DHA, which may stimulate blood circulation and increase the breakdown of fibrin, a protein involved in blood clotting and scar formation.[26][27] Omega−3 fatty acids reduce blood triglyceride levels but do not significantly change the level of LDL cholesterol or HDL cholesterol in the blood.[28][29] The American Heart Association position (2011) is that borderline elevated triglycerides, defined as 150–199 mg/dL, can be lowered by 0.5-1.0 grams of EPA and DHA per day; high triglycerides 200–499 mg/dL benefit from 1-2 g/day; and >500 mg/dL be treated under a physician's supervision with 2-4 g/day using a prescription product.[30]

Omega-3s have been studied in various mood disorders, such as postpartum depression, with some promising results. In bipolar disorder (manic depression), the omega-3s may be most effective for the depressed phase rather than the manic phase of the illness. The omega-3s have also been proposed to alleviate or prevent other psychiatric conditions including schizophrenia, borderline personality disorder, obsessive compulsive disorder, and attention deficit disorder. However, there is still not enough evidence to recommend the omega-3s in these conditions.

Today, some doctors are starting to measure the omega-3 index levels of their patients, just like they do with cholesterol levels. However, if your doctor does not offer this, several companies provide a quick and easy blood test you can conduct yourself, including OmegaQuant. This company is run by by Dr. William Harris, one of the scientists who initially developed the concept of the omega-3 index.
Omega-3 fatty acids are found primarily in fish oil and certain marine algae. Because depression appears less common in nations where people eat large amounts of fish, scientists have investigated whether fish oils may prevent and/or treat depression and other mood disorders. Two omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — are thought to have the most potential to benefit people with mood disorders.
The #1 Pharmacist Recommended Omega-3/Fish Oil brand,* Nature Made fish oil supply comes from deep ocean waters, not farm-raised fish. State-of-the-art purification processes remove mercury and ensure high levels of fish oil purity and concentration, guaranteed to pass the stringent standards of the Global Organization for EPA and DHA Omega-3 Voluntary Monograph.‡

The US National Institutes of Health lists three conditions for which fish oil and other omega-3 sources are most highly recommended: hypertriglyceridemia (high triglyceride level), preventing secondary cardiovascular disease, and hypertension (high blood pressure). It then lists 27 other conditions for which there is less evidence. It also lists possible safety concerns: "Intake of 3 grams per day or greater of omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil/omega-3 fatty acids may increase the risk of hemorrhagic (bleeding) stroke."[12]

Why would someone foul a perfectly good box of rotini with omega 3 oils? This is based on the belief that omega 3 fatty acids reduce heart disease and vascular risk, probably through reducing blood pressure and cholesterol. This is a plausible claim, but as we see over and over again in medicine, plausibility (while nice) is insufficient as a basis for clinical claims.
Fish oil is a concentrated source of omega-3 fats, which are also called ω-3 fatty acids or n-3 fatty acids. To get more scientific, omega-3s are long-chain polyunsaturated fatty acids, or PUFAs. Our bodies are able to make most of the fats we need need, but that’s not true for omega-3 fatty acids. When it comes to these essential fats, we need to get them from omega-3 foods or supplements.
We’ve already seen that fish oil can help with depression-like symptoms in rats, but what about people? A study published in the journal Nutritional Neuroscience evaluated the effects of fish oil supplementation on prefrontal metabolite concentrations in adolescents with major depressive disorder. Researchers found that there was a 40 percent decrease in major depression disorder symptoms in addition to marked improvements in amino acid and nutrition content in the brain, specifically, the right dorsolateral prefrontal cortex. (21)

Omega 3 is a type of fat. Small amounts of omega 3 fats are essential for good health, and they can be found in the food that we eat. The main types of omega 3 fatty acids are; alpha­linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).  ALA is normally found in fats from plant foods, such as nuts and seeds (walnuts and rapeseed are rich sources). EPA and DHA, collectively called long chain omega 3 fats, are naturally found in fatty fish, such as salmon and fish oils including cod liver oil.
Fish oil seems to be a subject of controversy. Some people swear by it, and there are thousands of clinical trials out now trying to study what the latest and greatest thing about the supplement is. The Natural Standard does a really good job collecting and gathering data for those who are interested in delving through what fish oil may or may not be doing to us. Definitive answers, however, may take a little while to get.
In 2016, AHRQ reviewed 143 studies that evaluated the effects of giving omega-3 supplements to pregnant or breastfeeding women or giving formulas with added DHA to infants. They found that when women took omega-3 supplements during pregnancy, their babies’ birth weight was slightly higher, but the risk of an undesirably low birth weight did not change. Also, when women took omega-3 supplements during pregnancy, their pregnancies lasted a little longer, but there was no effect on the risk of premature birth. Omega-3s were not found to have effects on any other aspects of the mothers’ or infants’ health or the infants’ long-term development. Aspects of the infants’ health that were not shown to be affected by omega-3s include growth after birth, visual acuity, long-term neurological and cognitive development, and the risks of autism, ADHD, learning disorders, and allergies.
In a 2009 joint study by the USDA and researchers at Clemson University in South Carolina, grass-fed beef was compared with grain-finished beef. The researchers found that grass-finished beef is higher in moisture content, 42.5% lower total lipid content, 54% lower in total fatty acids, 54% higher in beta-carotene, 288% higher in vitamin E (alpha-tocopherol), higher in the B-vitamins thiamin and riboflavin, higher in the minerals calcium, magnesium, and potassium, 193% higher in total omega−3s, 117% higher in CLA (cis-9, trans-11 octadecenoic acid, a cojugated linoleic acid, which is a potential cancer fighter), 90% higher in vaccenic acid (which can be transformed into CLA), lower in the saturated fats linked with heart disease, and has a healthier ratio of omega−6 to omega−3 fatty acids (1.65 vs 4.84). Protein and cholesterol content were equal.[86]
In fact, dietary fat intake has been among the most widely studied dietary risk factors for breast and prostate cancers. Two studies from 2002 explain how omega-3 can protect against breast cancer. BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer gene 2) are two tumor suppressor genes that, when functioning normally, help repair DNA damage, a process that also prevents tumor development.
Fish oil is a commonly used dietary supplement, with sales in the U.S. alone reaching $976 million in 2009.[48] Problems of quality have been identified in periodic tests by independent researchers of marketed supplements containing fish oil and other marine oils. These problems include contamination, inaccurate listing of EPA and DHA levels, spoilage and formulation issues.[49]
Healthy cells require a delicate balance of EPA and DHA and the body employs clever mechanisms to support this natural equilibrium. DHA levels are self-regulated through inhibiting the activity of the enzyme delta-6 desaturase – the very enzyme that supports the conversion of EPA into DHA – to ensure levels of DHA do not become too high. It is therefore possible to have too much preformed DHA, if our supplement intake exceeds the body’s needs.
A scientific review in 2014 evaluated study findings on omega-3 intake in relation to the prevention and treatment of breast cancer, the most prevalent cancer among women. The review found that EPA and DHA, as well as ALA, can differentially inhibit breast tumor development. According to this review, there is solid evidence to support the use of omega-3s as “a nutritional intervention in the treatment of breast cancer to enhance conventional therapeutics, or potentially lowering effective doses.” (16) Additionally, a 2016 study found that “very high fish consumption in early adulthood to midlife may be associated with decreased risk of breast cancer.” (17)
Reduce Metabolic Syndrome Symptoms: The cluster of risk factors known as metabolic syndrome includes abdominal obesity, high blood sugar, high triglycerides, high blood pressure and low HDL cholesterol. These risk factors are indicative of a high chance you might develop heart disease, stroke or diabetes. Multiple studies have found omega-3 supplementation improve the symptoms of metabolic syndrome and may help to protect you from the related diseases. (22, 23, 24, 25)

Dyerberg, J., Eskesen, D. C., Andersen, P. W., Astrup, A., Buemann, B., Christensen, J. H., Clausen, P., Rasmussen, B. F., Schmidt, E. B., Tholstrup, T., Toft, E., Toubro, S., and Stender, S. Effects of trans- and n-3 unsaturated fatty acids on cardiovascular risk markers in healthy males. An 8 weeks dietary intervention study. Eur.J.Clin.Nutr. 2004;58(7):1062-1070. View abstract.
High blood pressure. Fish oil seems to slightly lower blood pressure in people with moderate to very high blood pressure. Some types of fish oil might also reduce blood pressure in people with slightly high blood pressure, but results are inconsistent. Fish oil seems to add to the effects of some, but not all, blood pressure-lowering medications. However, it doesn't seem to reduce blood pressure in people with uncontrolled blood pressure who are already taking blood pressure-lowering medications.