The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), found in plant oils, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both commonly found in marine oils. Marine algae and phytoplankton are primary sources of omega−3 fatty acids. Common sources of plant oils containing ALA include walnut, edible seeds, clary sage seed oil, algal oil, flaxseed oil, Sacha Inchi oil, Echium oil, and hemp oil, while sources of animal omega−3 fatty acids EPA and DHA include fish, fish oils, eggs from chickens fed EPA and DHA, squid oils, and krill oil. Dietary supplementation with omega−3 fatty acids does not appear to affect the risk of death, cancer or heart disease. Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes or any vascular disease outcomes.
Studies have also found that omega-3 fatty acids from fish oil are associated with improved survival rates for heart attack victims. A study published in the medical journal Circulation found that people who took a high dose of fish oil each for six months following the occurrence of a heart attack actually improved their hearts’ overall functioning and also reduced biomarkers of systemic inflammation. (20)
Dry eye. Higher intake of fish oil from the diet has been linked to a lower risk of dry eye in women. But the effects of fish oil in people with dry eye are inconsistent. Some research shows that fish oil reduces dry eye symptoms such as pain, blurred vision, and sensitivity. But fish oil doesn’t seem to improve other signs and symptoms of dry eye such as tear production and damage to the surface of the eye. Taking fish oil also doesn’t improve signs and symptoms of dry eye when used with other dry eye treatments.
The DART study, published in 1989, was the first randomized trial to show the efficacy of fish oil on CAD.37 In the trial, 2033 post-MI patients were randomized to receive 3 types of diets: a diet that was either high in cereal fiber, polyunsaturated fat, or fish oil. The fish oil group consumed 200 to 400 g/wk of fatty fish (2 portions of fish per week) or 0.5 g/d of Maxepa fish oil supplement. At 2 years, the primary end point of all-cause mortality was reduced by 29% in the fish oil group, whereas no improvement was seen in the other dietary advice groups.
Omega−3 fatty acids are important for normal metabolism. Mammals are unable to synthesize omega−3 fatty acids, but can obtain the shorter-chain omega−3 fatty acid ALA (18 carbons and 3 double bonds) through diet and use it to form the more important long-chain omega−3 fatty acids, EPA (20 carbons and 5 double bonds) and then from EPA, the most crucial, DHA (22 carbons and 6 double bonds). The ability to make the longer-chain omega−3 fatty acids from ALA may be impaired in aging. In foods exposed to air, unsaturated fatty acids are vulnerable to oxidation and rancidity.
Fish oil is also used for diabetes, prediabetes, 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.