What is it?Fish oil can be obtained from eating fish or by taking supplements. Fish that are especially rich in the beneficial oils known as omega-3 fatty acids include mackerel, tuna, salmon, sturgeon, mullet, bluefish, anchovy, sardines, herring, trout, and menhaden. They provide about 1 gram of omega-3 fatty acids in about 3.5 ounces of fish.  Fish oil supplements are usually made from mackerel, herring, tuna, halibut, salmon, cod liver, whale blubber, or seal blubber. Fish oil supplements often contain small amounts of vitamin E to prevent spoilage. They might also be combined with calcium, iron, or vitamins A, B1, B2, B3, C, or D. Fish oil is used for a wide range of conditions. It is most often used for conditions related to the heart and blood system. Some people use fish oil to lower blood pressure or triglyceride levels (fats related to cholesterol). Fish oil has also been tried for preventing heart disease or stroke. The scientific evidence suggests that fish oil really does lower high triglycerides, and it also seems to help prevent heart disease and stroke when taken in the recommended amounts. Ironically, taking too much fish oil can actually increase the risk of stroke. Fish may have earned its reputation as "brain food" because some people eat fish to help with depression, psychosis, attention deficit-hyperactivity disorder (ADHD), Alzheimer's disease, and other thinking disorders. Some people use fish oil for dry eyes, glaucoma, and age-related macular degeneration (AMD), a very common condition in older people that can lead to serious sight problems. Women sometimes take fish oil to prevent painful periods; breast pain; and complications associated with pregnancy such as miscarriage, high blood pressure late in pregnancy, and early delivery. Fish oil is also used for diabetes, asthma, developmental coordination disorders, movement disorders, dyslexia, obesity, kidney disease, weak bones (osteoporosis), certain diseases related to pain and swelling such as psoriasis, and preventing weight loss caused by some cancer drugs. Fish oil is sometimes used after heart transplant surgery to prevent high blood pressure and kidney damage that can be caused by the surgery itself or by drugs used to reduce the chances that the body will reject the new heart. Fish oil is sometimes used after coronary artery bypass surgery. It seems to help keep the blood vessel that has been rerouted from closing up. When fish oil is obtained by eating fish, the way the fish is prepared seems to make a difference. Eating broiled or baked fish appears to reduce the risk of heart disease, but eating fried fish or fish sandwiches not only cancels out the benefits of fish oil, but may actually increase heart disease risk. Two of the most important omega-3 fatty acids contained in fish oil are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). See separate listings for EPA and DHA. How effective is it?Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.
The effectiveness ratings for FISH OIL are as follows: 
Effective for...- High triglycerides. High triglycerides are associated with heart disease and untreated diabetes. To reduce the risk of heart disease, doctors believe it is important to keep triglycerides below a certain level. Doctors usually recommend increasing physical activity and restricting dietary fat to lower triglycerides. Sometimes they also prescribe drugs such as gemfibrozil (Lopid) for use in addition to these lifestyle changes. Now researchers believe that fish oil, though not as effective as gemfibrozil, can reduce triglyceride levels by 20% to 50%. One particular fish oil supplement called Lovaza has been approved by the FDA to lower triglycerides. Lovaza contains 465 milligrams of EP and 375 milligrams of DHA in 1-gram capsules.
Likely effective for...- Heart disease. Fish oil may be effective in keeping people with healthy hearts free of heart disease. People who already have heart disease may be able to lower their risk of dying from heart disease by taking fish oil. Though not all researchers agree, some investigators believe that fish oil may be even more effective in reducing death from heart attacks than a group of commonly used cholesterol-lowering drugs called "statins."
Possibly effective for...- High blood pressure. Fish oil seems to produce modest reductions in blood pressure in people with high blood pressure. The omega-3 fatty acids in fish oil seem to be able to expand blood vessels, and this brings blood pressure down.
- Rheumatoid arthritis. Fish oil alone, or in combination with the drug naproxen (Naprosyn), seems to help people with rheumatoid arthritis get over morning stiffness faster. People who take fish oil can sometimes reduce their use of pain medications such as nonsteroidal anti-inflammatory drugs (NSAIDs).
- Menstrual pain (dysmenorrhea). Taking fish oil alone or in combination with vitamin B12 seems to improve painful periods and reduce the need for pain medications such as nonsteroidal anti-inflammatory drugs (NSAIDS).
- Attention deficit-hyperactivity disorder (ADHD) in children. Taking fish oil seems to improve thinking skills and behavior in 8 to 12 year-old children with ADHD.
- Raynaud's syndrome. There's some evidence that taking fish oil can improve cold tolerance in some people with the usual form of Raynaud's syndrome. But people with Raynaud's syndrome caused by a condition called progressive systemic sclerosis don't seem to benefit from fish oil supplements.
- Stroke. Moderate fish consumption (once or twice a week) seems to lower the risk of having a stroke by as much as 27%. However, eating fish doesn't lower stroke risk in people who are already taking aspirin for prevention. On the other hand, very high fish consumption (more than 46 grams of fish per day) seems to increase stroke risk, perhaps even double it.
- Weak bones (osteoporosis). Taking fish oil alone or in combination with calcium and evening primrose oil seems to slow bone loss rate and increase bone density at the thigh bone (femur) and spine in elderly people with osteoporosis.
- Hardening of the arteries (atherosclerosis). Fish oil seems to slow or slightly reverse the progress of atherosclerosis in the arteries serving the heart (coronary arteries), but not in the arteries that bring blood up the neck to the head (carotid arteries).
- Kidney problems. Long-term use (two years) of fish oil 4-8 grams daily can slow the loss of kidney function in high-risk patients with a kidney disease called IgA nephropathy. Fish oil also seems to reduce the amount of protein in the urine of people who have kidney disease as a result of diabetes.
- Bipolar disorder. Taking fish oil with the usual treatments for bipolar disorder seems to improve symptoms of depression and increase the length of time between episodes of depression. But fish oil doesn't seem to improve manic symptoms in people with bipolar disorder.
- Psychosis. Taking a fish oil supplement might help prevent full psychotic illness from developing in people with mild symptoms. This has only been tested in teenagers and adults up to age 25.
- Weight loss. Some evidence shows that eating fish improves weight loss and decreases blood sugar in overweight people and people with high blood pressure. Preliminary research also shows that taking a specific fish oil supplement 6 grams daily (Hi-DHA, NuMega), providing 260 mg DHA/gram and 60 mg EPA/gram, significantly decreases body fat when combined with exercise.
- Endometrial cancer. There is some evidence that women who regularly eat about two servings of fatty fish per week have a reduced risk of developing endometrial cancer.
- Age-related eye disease (age-related macular degeneration, AMD). There is some evidence that people who eat fish more than once per week have a lower risk of developing age-related macular degeneration.
- Reducing the risk of blood vessel re-blockage after heart bypass surgery or "balloon" catheterization (balloon angioplasty). Fish oil appears to decrease the rate of re-blockage up to 26% when given for one month before the procedure and continued for one month thereafter. Apparently, taking fish oil before surgery is important. When taken for less than one month before angioplasty, fish oil doesn't help protect the blood vessel against closing down.
- Recurrent miscarriage in pregnant women with antiphospholipid syndrome. Taking fish oil seems to prevent miscarriage and increase live birth rate in pregnant women with a condition called antiphospholipid syndrome.
- High blood pressure and kidney problems after heart transplant. Taking fish oil seems to preserve kidney function and reduce the long-term continuous rise in blood pressure after heart transplantation.
- Damage to the kidneys and high blood pressure caused by taking a drug called cyclosporine. Cyclosporine is a medication that reduces the chance of organ rejection after an organ transplant. Fish oil might help reduce some of the unwanted side effects of treatment with this drug.
- Movement disorder in children (dyspraxia). Taking fish oil orally, in combination with evening primrose oil, thyme oil, and vitamin E (Efalex, Efamol Ltd), seems to improve movement disorders in children with dyspraxia.
- Developmental coordination disorder. A combination of fish oil (80%) and evening primrose oil (20%) seems to improve reading, spelling, and behavior when given to children age 5-12 years with developmental coordination disorder. However, it doesn't seem to improve motor skills.
- Preventing blockage of grafts used in kidney dialysis. Taking fish oil orally seems to help prevent clot formation in hemodialysis grafts.
- Psoriasis. There is some evidence that administering fish oil intravenously (by IV) can decrease severe psoriasis symptoms. But taking fish oil by mouth doesn't seem to have any effect on psoriasis.
- High cholesterol. There is interest in using fish oil in combination with "statin" drugs for some people with high cholesterol. Doctors were worried at first that taking fish oil might interfere with statin treatment, but early studies show this is not a problem, at least with the statin called simvastatin. Scientists think fish oil may lower cholesterol by keeping it from being absorbed in the intestine. There is some evidence that using vitamin B12 along with fish oil might boost their ability to lower cholesterol.
- Coronary artery bypass surgery. Taking fish oil seems to prevent coronary artery bypass grafts from re-closing following coronary artery bypass surgery.
- Cancer-related weight loss. Taking a high dose (7.5 grams per day) of fish oil seems to slow weight loss in some cancer patients. Some researchers believe these patients eat more because the fish oil is fighting depression and improving their mood.
- Asthma. Some research suggests fish oil may lower the occurrence of asthma in infants and children when taken by women late in pregnancy. Furthermore, fish oil seems to improve airflow, reduce cough, and lower the need for medications in some children with asthma. However, fish oil treatment doesn't seem to provide the same benefit for adults.
Possibly ineffective for...- Gum infection (gingivitis).
- Liver disease.
- Leg pain due to blood flow problems (claudication).
- Preventing migraine headaches.
- Preventing muscle soreness caused by physical exercise.
- Breast pain.
- Skin rashes caused by allergic reactions.
- Stomach ulcers.
How does it work?
A lot of the benefit of fish oil seems to come from the omega-3 fatty acids that it contains. Interestingly, the body does not produce its own omega-3 fatty acids. Nor can the body make omega-3 fatty acids from omega-6 fatty acids, which are common in the Western diet. A lot of research has been done on EPA and DHA, two types of omega-3 acids that are often included in fish oil supplements.
Omega-3 fatty acids reduce pain and swelling. This may explain why fish oil is likely effective for psoriasis and dry eyes. These fatty acids also prevent the blood from clotting easily. this might make fish oil helpful for some heart conditions.
Fish oil is LIKELY SAFE for most people, including pregnant and breast-feeding women, when taken in low doses (3 grams or less per day). There are some safety concerns when fish oil is taken in high doses. Taking more than 3 grams per day might keep blood from clotting and can increase the chance of bleeding.
High doses of fish oil might also reduce the immune system's activity, reducing the body's ability to fight infection. This is a special concern for people taking medications to reduce their immune system's activity (organ transplant patients, for example) and the elderly.
Only take high doses of fish oil while under medical supervision.
Fish oil can cause side effects including belching, bad breath, heartburn, nausea, loose stools, rash, and nosebleeds. Taking fish oil supplements with meals or freezing them can often decrease these side effects.
Consuming large amounts of fish oil from some DIETARY sources is POSSIBLY UNSAFE. Some fish meats (especially shark, king mackerel, and farm-raised salmon) can be contaminated with mercury and other industrial and environmental chemicals, but fish oil supplements typically do not contain these contaminants. Special precautions & warnings:Liver disease: Fish oil might increase the risk of bleeding.
Fish or seafood allergy: Some people who are allergic to seafood such as fish might also be allergic to fish oil supplements. There is no reliable information showing how likely people with seafood allergy are to have an allergic reaction to fish oil; however, until more is known advise patients allergic to seafood to avoid or use fish oil supplements cautiously.
Bipolar disorder: Taking fish oil might increase some of the symptoms of this condition.
Depression: Taking fish oil might increase some of the symptoms of this condition.
Diabetes: There is some concern that taking high doses of fish oil might make the control of blood sugar more difficult.
High blood pressure: Fish oil can lower blood pressure and might cause blood pressure to drop too low in people who are being treated with blood pressure-lowering medications.
HIV/AIDS and other conditions in which the immune system response is lowered: Higher doses of fish oil can lower the body's immune system response. This could be a problem for people whose immune system is already weak.
An implanted defibrillator (a surgically placed device to prevent irregular heartbeat): Some, but not all, research suggests that fish oil might increase the risk of irregular heartbeat in patients with an implanted defibrillator. Stay on the safe side by avoiding fish oil supplements.
The following doses have been studied in scientific research: BY MOUTH:- For high triglycerides: 1-4 grams/day of fish oil.
- For high blood pressure: Either 4 grams of fish oil or fish oil providing 2.04 grams of EPA and 1.4 grams of DHA per day.
- For atrial fibrillation (one of the chambers of the heart doesn't empty properly and this increases the risk of blood clot formation leading to stroke): Eating tuna or baked or broiled fish providing omega-3 fatty acids (fish oil) one or more times per week seems to reduce the risk of atrial fibrillation in patients aged 65 or older compared to consuming fish once per month or less. But there is no benefit from eating fried fish or a fish sandwich.
- For kidney problems related to using cyclosporine to prevent organ transplant rejection: 12 grams/day containing 2.2 grams EPA and 1.4 grams DHA.
- For reducing the overall risk of death and risk of sudden death in patients with coronary heart disease: Fish oil providing 0.3-6 grams of EPA with 0.6 to 3.7 grams of DHA.
- For asthma in children: Fish oil providing 17-26.8 mg/kg EPA and 7.3-11.5 mg/kg DHA for reducing symptoms. Maternal ingestion of fish oil 4 grams daily, providing 32% EPA and 23% DHA with tocopherol, during late-phase pregnancy has been used for preventing the development of asthma in children.
- For preventing childhood allergies: Maternal ingestion of fish oil 4 grams daily, providing 32% EPA and 23% DHA with tocopherol, during late-phase pregnancy.
- For preventing childhood atopic dermatitis: Maternal ingestion of fish oil 4 grams daily, providing 32% EPA and 23% DHA with tocopherol, during late-phase pregnancy.
- For treating asthma: 17-26.8 mg/kg EPA and 7.3-11.5 mg/kg DHA.
- For preventing and reversing the progression of hardening of the arteries: 6 grams/day of fish oil for the first three months, followed by 3 grams/day thereafter.
- For rheumatoid arthritis: Fish oil providing 3.8 grams/day of EPA and 2 grams/day DHA.
- For attention deficit-hyperactivity disorder (ADHD): A specific supplement containing fish oil 400 mg and evening primrose oil 100 mg (Eye Q, Novasel) six capsules daily.
- For preventing miscarriage in women with antiphospholipid antibody syndrome and a history of past miscarriage: 5.1 grams fish oil with a 1.5 EPA:DHA ratio.
- For painful menstrual periods: A daily dose of EPA 1080 mg and DHA 720 mg.
- For Raynaud's syndrome: A daily dose of 3.96 grams EPA and 2.64 grams DHA.
- For weight loss: A daily serving of 2-7 ounces of fish containing approximately 3.65 grams omega-3 fatty acids (0.66 gram from EPA and 0.60 gram from DHA).
- For slowing weight loss in patients with cancer: 7.5 grams/day of fish oil providing EPA 4.7 grams and DHA 2.8 grams.
- For improving movement disorders in children with poor coordination (dyspraxia): Fish oil providing DHA 480 mg combined with 35 mg arachidonic acid and 96 mg gamma-alpha linoleic acid from evening primrose oil, 24 mg thyme oil, and 80 mg vitamin E (Efalex).
- For developmental coordination disorder in children: Fish oil providing EPA 558 mg and DHA 174 in 3 divided doses.
- For depression along with conventional antidepressants: Fish oil 9.6 grams/day.
- To prevent full psychosis from developing in people with mild symptoms: Fish oil 1.2 grams/day.
- For keeping veins open after coronary bypass surgery: 4 grams/day of fish oil containing EPA 2.04 grams and DHA 1.3 grams.
- For preventing the collapse of arteries opened by "balloon" therapy (PTCA): 6 grams/day of fish oil starting one month before PTCA and continuing one month after PTCA, followed by 3 grams of fish oil daily thereafter for six months.
- For reducing and preventing the long-term continuous rise in blood pressure and to preserve kidney function after heart transplantation: 4 grams/day of fish oil (46.5% EPA and 37.8% DHA).
- For preventing clotting after placement of a tube for dialysis: 6 grams/day of fish oil.
- For preserving kidney function in patients with severe IgA nephropathy: 4-8 grams/day of fish oil has been used.
- For combined high triglycerides and high cholesterol: Fish oil providing EPA 1800-2160 mg and DHA 1200-1440 mg combined with garlic powder 900-1200 mg/day has been used to lower total cholesterol, LDL, triglycerides, and the ratios of total cholesterol to HDL, and LDL to HDL.
- For salicylate intolerance: Fish oil 10 grams daily.
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