Fish oil is FDA approved to lower triglycerides levels, but it is also used for many other conditions. It is most often used for conditions related to the heart and blood system. Some people use fish oil to lower blood pressure, triglycerides and cholesterol levels. Fish oil has also been used for preventing heart disease or stroke, as well as for clogged arteries, chest pain, irregular heartbeat, bypass surgery, heart failure, rapid heartbeat, preventing blood clots, and high blood pressure after a heart transplant.
Fish oil is also used to for many kidney-related problems including kidney disease, kidney failure, and kidney complications related to diabetes, cirrhosis and heart transplantation.
Fish may have earned its reputation as "brain food" because some people eat fish to help with depression, bipolar disorder, psychosis, attention deficit-hyperactivity disorder (ADHD), Alzheimer's disease, developmental coordination disorder, migraine headache, epilepsy, schizophrenia, post-traumatic stress disorder, and mental impairment.
Fish oil is taken by mouth for stomach ulcers caused by Helicobacter pylori (H. pylori), inflammatory bowel disease, pancreatitis, an inherited disorder called phenylketonuria, allergy to salicylate, Crohn's disease, Behcet's syndrome, and Raynaud's syndrome.
Fish oil is also taken by mouth for weight loss, exercise performance and muscle strength, muscle soreness after exercise, pneumonia, cancer, lung disease, seasonal allergies, chronic fatigue syndrome, and for preventing blood vessels from re-narrowing after surgery to widen them.
Fish oil is also used for diabetes, pre-diabetes, asthma, a movement and coordination disorder called dyspraxia, dyslexia, eczema, autism, obesity, weak bones (osteoporosis), rheumatoid arthritis (RA), osteoarthritis, psoriasis, an autoimmune disease called systemic lupus erythematosus (SLE), multiple sclerosis, HIV/AIDS, cystic fibrosis, gum disease, Lyme disease, sickle cell disease, and preventing weight loss caused by some cancer drugs.
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 explain why fish oil is helpful for some heart conditions.